/usr/share/doc/gmt/html/GMT_Tutorial.html is in gmt-doc 4.5.11-1build1.
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<!--l. 12--><p class="noindent" >
</p><!--l. 14--><p class="noindent" ><span
class="ptmb8t-x-x-207">The Generic Mapping Tools</span>
</p><!--l. 17--><p class="noindent" ><img
src="images/GMT_covertext.png" alt="PIC"
/>
</p><!--l. 20--><p class="noindent" ><span
class="ptmb8t-x-x-248">Version 4.5.11</span>
</p><!--l. 24--><p class="noindent" ><span
class="ptmb8t-x-x-207">A Map-making Tutorial</span>
</p><!--l. 28--><p class="noindent" ><span
class="ptmb8t-x-x-120">by</span>
</p><!--l. 32--><p class="noindent" ><span
class="ptmb8t-x-x-207">Pål (Paul) Wessel</span>
</p><!--l. 36--><p class="noindent" ><span
class="ptmb8t-x-x-144">School of Ocean and Earth Science and Technology</span>
</p><!--l. 37--><p class="noindent" ><span
class="ptmb8t-x-x-144">University of Hawai’i at M</span><span
class="ptmb8t-x-x-144">ā</span><span
class="ptmb8t-x-x-144">noa</span>
</p><!--l. 41--><p class="noindent" ><span
class="ptmb8t-x-x-120">and</span>
</p><!--l. 45--><p class="noindent" ><span
class="ptmb8t-x-x-207">Walter H. F. Smith</span>
</p><!--l. 49--><p class="noindent" ><span
class="ptmb8t-x-x-144">Laboratory for Satellite Altimetry</span>
</p><!--l. 50--><p class="noindent" ><span
class="ptmb8t-x-x-144">NOAA/NESDIS</span>
</p><!--l. 54--><p class="noindent" ><span
class="ptmb8t-x-x-120">November 2013</span>
</p><!--l. 57--><p class="noindent" ><img
src="images/GMT_coverlogo.png" alt="PIC"
/></p></div>
<a
id="Q1-1-1"></a>
<h2 class="likechapterHead"><a
id="x1-1000"></a>Contents</h2> <div class="tableofcontents">
<span class="chapterToc" > <a
href="#Q1-1-1">Front page</a></span>
<br /> <span class="chapterToc" > <a
href="#Q1-1-4">INTRODUCTION</a></span>
<br />  <span class="sectionToc" ><a
href="#Q1-1-6"><span
class="ptmb8t-">GMT</span> overview: History, philosophy, and usage</a></span>
<br />   <span class="subsectionToc" ><a
href="#Q1-1-8">Historical highlights</a></span>
<br />   <span class="subsectionToc" ><a
href="#Q1-1-10">Philosophy</a></span>
<br />   <span class="subsectionToc" ><a
href="#Q1-1-12">Why is <span
class="ptmb8t-">GMT</span> so popular?</a></span>
<br />   <span class="subsectionToc" ><a
href="#Q1-1-14"><span
class="ptmb8t-">GMT</span> installation considerations</a></span>
<br /> <span class="chapterToc" >1 <a
href="#x1-80001" id="QQ2-1-15">SESSION ONE</a></span>
<br />  <span class="sectionToc" >1.1 <a
href="#x1-90001.1" id="QQ2-1-16">Tutorial setup</a></span>
<br />  <span class="sectionToc" >1.2 <a
href="#x1-100001.2" id="QQ2-1-17">The <span
class="ptmb8t-">GMT</span> environment: What happens when you run <span
class="ptmb8t-">GMT</span>?</a></span>
<br />   <span class="subsectionToc" >1.2.1 <a
href="#x1-110001.2.1" id="QQ2-1-19">Input data</a></span>
<br />   <span class="subsectionToc" >1.2.2 <a
href="#x1-120001.2.2" id="QQ2-1-20">Job Control</a></span>
<br />   <span class="subsectionToc" >1.2.3 <a
href="#x1-130001.2.3" id="QQ2-1-21">Output data</a></span>
<br />  <span class="sectionToc" >1.3 <a
href="#x1-140001.3" id="QQ2-1-22">The UNIX Environment: Entry Level Knowledge</a></span>
<br />   <span class="subsectionToc" >1.3.1 <a
href="#x1-150001.3.1" id="QQ2-1-23">Redirection</a></span>
<br />   <span class="subsectionToc" >1.3.2 <a
href="#x1-160001.3.2" id="QQ2-1-24">Piping
(<!--l. 25--><math
xmlns="http://www.w3.org/1998/Math/MathML"
display="inline" ><mo
class="MathClass-rel">|</mo></math>)</a></span>
<br />   <span class="subsectionToc" >1.3.3 <a
href="#x1-170001.3.3" id="QQ2-1-25">Standard error (<span
class="ptmri8t-">stderr</span>)</a></span>
<br />   <span class="subsectionToc" >1.3.4 <a
href="#x1-180001.3.4" id="QQ2-1-26">File name expansion or “wild cards”</a></span>
<br />  <span class="sectionToc" >1.4 <a
href="#x1-200001.4" id="QQ2-1-29">Laboratory Exercises</a></span>
<br />   <span class="subsectionToc" >1.4.1 <a
href="#x1-210001.4.1" id="QQ2-1-30">Linear projection</a></span>
<br />   <span class="subsectionToc" >1.4.2 <a
href="#x1-230001.4.2" id="QQ2-1-32">Logarithmic projection</a></span>
<br />   <span class="subsectionToc" >1.4.3 <a
href="#x1-250001.4.3" id="QQ2-1-34">Mercator projection</a></span>
<br />   <span class="subsectionToc" >1.4.4 <a
href="#x1-270001.4.4" id="QQ2-1-37">Albers projection</a></span>
<br />   <span class="subsectionToc" >1.4.5 <a
href="#x1-290001.4.5" id="QQ2-1-39">Orthographic projection</a></span>
<br />   <span class="subsectionToc" >1.4.6 <a
href="#x1-310001.4.6" id="QQ2-1-41">Eckert IV and VI projection</a></span>
<br /> <span class="chapterToc" >2 <a
href="#x1-330002" id="QQ2-1-43">SESSION TWO</a></span>
<br />  <span class="sectionToc" >2.1 <a
href="#x1-340002.1" id="QQ2-1-44">General Information</a></span>
<br />   <span class="subsectionToc" >2.1.1 <a
href="#x1-350002.1.1" id="QQ2-1-48">Examples</a></span>
<br />   <span class="subsectionToc" >2.1.2 <a
href="#x1-360002.1.2" id="QQ2-1-49">Exercises</a></span>
<br />   <span class="subsectionToc" >2.1.3 <a
href="#x1-370002.1.3" id="QQ2-1-50">More exercises</a></span>
<br />  <span class="sectionToc" >2.2 <a
href="#x1-380002.2" id="QQ2-1-51">Plotting text strings</a></span>
<br />  <span class="sectionToc" >2.3 <a
href="#x1-390002.3" id="QQ2-1-57">Exercises</a></span>
<br /> <span class="chapterToc" >3 <a
href="#x1-400003" id="QQ2-1-58">SESSION THREE</a></span>
<br />  <span class="sectionToc" >3.1 <a
href="#x1-410003.1" id="QQ2-1-59">Contouring gridded data sets</a></span>
<br />   <span class="subsectionToc" >3.1.1 <a
href="#x1-420003.1.1" id="QQ2-1-61">Exercises</a></span>
<br />  <span class="sectionToc" >3.2 <a
href="#x1-430003.2" id="QQ2-1-62">Gridding of arbitrarily spaced data</a></span>
<br />   <span class="subsectionToc" >3.2.1 <a
href="#x1-440003.2.1" id="QQ2-1-63">Nearest neighbor gridding</a></span>
<br />   <span class="subsectionToc" >3.2.2 <a
href="#x1-460003.2.2" id="QQ2-1-67">Gridding with Splines in Tension</a></span>
<br />   <span class="subsectionToc" >3.2.3 <a
href="#x1-470003.2.3" id="QQ2-1-69">Preprocessing</a></span>
<br />  <span class="sectionToc" >3.3 <a
href="#x1-480003.3" id="QQ2-1-71">Exercises</a></span>
<br /> <span class="chapterToc" >4 <a
href="#x1-490004" id="QQ2-1-72">SESSION FOUR</a></span>
<br />  <span class="sectionToc" >4.1 <a
href="#x1-500004.1" id="QQ2-1-73">Cpt files</a></span>
<br />   <span class="subsectionToc" >4.1.1 <a
href="#x1-510004.1.1" id="QQ2-1-76">Exercises</a></span>
<br />  <span class="sectionToc" >4.2 <a
href="#x1-520004.2" id="QQ2-1-77">Illumination and intensities</a></span>
<br />  <span class="sectionToc" >4.3 <a
href="#x1-530004.3" id="QQ2-1-78">Color images</a></span>
<br />   <span class="subsectionToc" >4.3.1 <a
href="#x1-540004.3.1" id="QQ2-1-82">Exercises</a></span>
<br />  <span class="sectionToc" >4.4 <a
href="#x1-550004.4" id="QQ2-1-83">Multi-dimensional maps</a></span>
<br />   <span class="subsectionToc" >4.4.1 <a
href="#x1-560004.4.1" id="QQ2-1-84">Exercises</a></span>
<br />  <span class="sectionToc" >4.5 <a
href="#x1-570004.5" id="QQ2-1-85">Perspective views</a></span>
<br />   <span class="subsectionToc" >4.5.1 <a
href="#x1-580004.5.1" id="QQ2-1-87">Mesh-plot</a></span>
<br />   <span class="subsectionToc" >4.5.2 <a
href="#x1-600004.5.2" id="QQ2-1-89">Color-coded view</a></span>
<br /> <span class="chapterToc" >5 <a
href="#x1-620005" id="QQ2-1-91">References</a></span>
</div>
<h2 class="likechapterHead"><a
id="x1-2000"></a>INTRODUCTION</h2> <a
id="Q1-1-4"></a> <a
id="dx1-2001"></a>
<!--l. 32--><p class="noindent" >The purpose of this tutorial is to introduce new users to <a
href="http://gmt.soest.hawaii.edu" ><span
class="ptmb8t-">GMT</span></a>, outline the <a
href="http://gmt.soest.hawaii.edu" ><span
class="ptmb8t-">GMT</span></a> environment, and enable you to
make several forms of graphics without having to know too much about <span
class="ptmri8t-">UNIX</span> and <span
class="ptmri8t-">UNIX</span> tools. We will not be
able to cover all aspects of <a
href="http://gmt.soest.hawaii.edu" ><span
class="ptmb8t-">GMT</span></a> nor will we necessarily cover the selected topics in sufficient detail.
Nevertheless, it is hoped that the exposure will prompt the users to improve their <a
href="http://gmt.soest.hawaii.edu" ><span
class="ptmb8t-">GMT</span></a> and <span
class="ptmri8t-">UNIX</span> skills after
completion of this short tutorial.
</p>
<h3 class="likesectionHead"><a
id="x1-3000"></a><a
href="http://gmt.soest.hawaii.edu" ><span
class="ptmb8t-">GMT</span></a> overview: History, philosophy, and usage</h3>
<a
id="Q1-1-6"></a>
<!--l. 44--><p class="noindent" >
</p>
<h4 class="likesubsectionHead"><a
id="x1-4000"></a>Historical highlights</h4>
<a
id="Q1-1-8"></a>
<a
id="dx1-4001"></a>
<!--l. 48--><p class="noindent" >The <a
href="http://gmt.soest.hawaii.edu" ><span
class="ptmb8t-">GMT</span></a> system was initiated in late 1987 at Lamont-Doherty Earth Observatory, Columbia University by
graduate students Paul Wessel and Walter H. F. Smith. Version 1 was officially introduced to Lamont scientists in
July 1988. <a
href="http://gmt.soest.hawaii.edu" ><span
class="ptmb8t-">GMT</span></a> 1 migrated by word of mouth (and tape) to other institutions in the United States, UK, Japan, and
France and attracted a small following. Paul took a Post-doctoral position at SOEST in December 1989 and
continued the <a
href="http://gmt.soest.hawaii.edu" ><span
class="ptmb8t-">GMT</span></a> development. Version 2.0 was released with an article in EOS, October 1991, and quickly
spread worldwide. We obtained NSF-funding for <a
href="http://gmt.soest.hawaii.edu" ><span
class="ptmb8t-">GMT</span></a> version 3.0 in 1993 which was released with another
article in EOS on August 15, 1995. Significantly improved versions (3.1-3.3, 3.3.1–6), 3.4, 3.4.1–5,
and 4.0–4.5.9 were released between November 1998 and April 2013, culminating in the November
2013 introduction of 4.5.11. <a
href="http://gmt.soest.hawaii.edu" ><span
class="ptmb8t-">GMT</span></a> now is used by ten thousands of users worldwide in a broad range of
disciplines.
</p><!--l. 63--><p class="noindent" >
</p>
<h4 class="likesubsectionHead"><a
id="x1-5000"></a>Philosophy</h4>
<a
id="Q1-1-10"></a>
<a
id="dx1-5001"></a>
<!--l. 67--><p class="noindent" ><a
href="http://gmt.soest.hawaii.edu" ><span
class="ptmb8t-">GMT</span></a> follows the <span
class="ptmri8t-">UNIX</span> philosophy in which complex tasks are broken down into smaller and more manageable
components. Individual <a
href="http://gmt.soest.hawaii.edu" ><span
class="ptmb8t-">GMT</span></a> modules are small, easy to maintain, and can be used as any other <span
class="ptmri8t-">UNIX</span> tool.
<a
href="http://gmt.soest.hawaii.edu" ><span
class="ptmb8t-">GMT</span></a> is written in the ANSI C programming language (very portable), is POSIX compliant, and is independent of
hardware constraints (e.g., memory). <a
href="http://gmt.soest.hawaii.edu" ><span
class="ptmb8t-">GMT</span></a> was deliberately written for command-line usage, not a windows
environment, in order to maximize flexibility. We standardized early on to use <span
class="ptmri8t-">PostScript</span> output
instead of other graphics formats. Apart from the built-in support for coastlines, <a
href="http://gmt.soest.hawaii.edu" ><span
class="ptmb8t-">GMT</span></a> completely
decouples data retrieval from the main <a
href="http://gmt.soest.hawaii.edu" ><span
class="ptmb8t-">GMT</span></a> programs. <a
href="http://gmt.soest.hawaii.edu" ><span
class="ptmb8t-">GMT</span></a> uses architecture-independent file
formats.
</p><!--l. 79--><p class="noindent" >
</p>
<h4 class="likesubsectionHead"><a
id="x1-6000"></a>Why is <a
href="http://gmt.soest.hawaii.edu" ><span
class="ptmb8t-">GMT</span></a> so popular?</h4>
<a
id="Q1-1-12"></a>
<a
id="dx1-6001"></a>
<!--l. 83--><p class="noindent" >The price is right! Also, <a
href="http://gmt.soest.hawaii.edu" ><span
class="ptmb8t-">GMT</span></a> offers unlimited flexibility since it can be called from the command line, inside
scripts, and from user programs. <a
href="http://gmt.soest.hawaii.edu" ><span
class="ptmb8t-">GMT</span></a> has attracted many users because of its high quality <span
class="ptmri8t-">PostScript</span> output.
<a
href="http://gmt.soest.hawaii.edu" ><span
class="ptmb8t-">GMT</span></a> easily installs on almost any computer.
</p><!--l. 88--><p class="noindent" >
</p>
<h4 class="likesubsectionHead"><a
id="x1-7000"></a><a
href="http://gmt.soest.hawaii.edu" ><span
class="ptmb8t-">GMT</span></a> installation considerations</h4>
<a
id="Q1-1-14"></a>
<a
id="dx1-7001"></a>
<!--l. 92--><p class="noindent" ><a
href="http://gmt.soest.hawaii.edu" ><span
class="ptmb8t-">GMT</span></a> has been installed on machines ranging from super-computers to lap-top PCs. <a
href="http://gmt.soest.hawaii.edu" ><span
class="ptmb8t-">GMT</span></a> only contains
some 100,000 lines of code and has modest space/memory requirements. Minimum requirements are
<a
id="dx1-7002"></a>
</p>
<ul class="itemize1">
<li class="itemize">The netCDF library 3.4 or higher (free from www.unidata.edu).
</li>
<li class="itemize">A C Compiler (free from www.gnu.org).
</li>
<li class="itemize">About 100 Mb disk space (70 Mb additional for full- and high-resolution coast-lines).
</li>
<li class="itemize">About 32 Mb memory.
</li></ul>
<!--l. 107--><p class="indent" > In addition, we recommend access to a <span
class="ptmri8t-">PostScript</span> printer or equivalent (e.g., <span
class="ptmbo8t-">ghostscript</span><a
id="dx1-7003"></a>),
<span
class="ptmri8t-">PostScript</span> previewer (e.g., <span
class="ptmbo8t-">gv</span><a
id="dx1-7004"></a> (ghostview)), any flavor of the <span
class="ptmri8t-">UNIX</span> operating system, and more disk space and
memory.
</p>
<h2 class="chapterHead"><span class="titlemark">Chapter 1</span><br /><a
id="x1-80001"></a>SESSION ONE</h2>
<h3 class="sectionHead"><span class="titlemark">1.1 </span> <a
id="x1-90001.1"></a>Tutorial setup</h3>
<!--l. 115--><p class="noindent" >
</p><ol class="enumerate1" >
<li
class="enumerate" id="x1-9002x1">We assume that <a
href="http://gmt.soest.hawaii.edu" ><span
class="ptmb8t-">GMT</span></a> has been properly and fully installed and that the <a
href="http://gmt.soest.hawaii.edu" ><span
class="ptmb8t-">GMT</span></a> executables are in your
executable path described in the <a
href="http://gmt.soest.hawaii.edu" ><span
class="ptmb8t-">GMT</span></a> <span class="underline">README</span> file.
</li>
<li
class="enumerate" id="x1-9004x2">All <a
href="http://gmt.soest.hawaii.edu" ><span
class="ptmb8t-">GMT</span></a> man pages, documentation, and example scripts are available from the <a
href="http://gmt.soest.hawaii.edu" ><span
class="ptmb8t-">GMT</span></a> documentation
web page. It is assumed these pages have been installed locally at your site; if not they are always
available from the main <a
href="http://gmt.soest.hawaii.edu" >GMT home page</a>.
</li>
<li
class="enumerate" id="x1-9006x3">We recommend you create a sub-directory called <span class="underline">tutorial</span>, cd into that directory, and copy all
the tutorial files directly there. Depending on your installation the tutorial files are likely in
<span class="underline">/usr/share/doc/gmt/tutorial</span>.
</li>
<li
class="enumerate" id="x1-9008x4">As we discuss <a
href="http://gmt.soest.hawaii.edu" ><span
class="ptmb8t-">GMT</span></a> principles it may be a good idea to consult the <a
href="http://gmt.soest.hawaii.edu" ><span
class="ptmb8t-">GMT</span></a> Technical Reference and
Cookbook for more detailed explanations.
</li>
<li
class="enumerate" id="x1-9010x5">The tutorial uses the supplemental <a
href="http://gmt.soest.hawaii.edu" ><span
class="ptmb8t-">GMT</span></a> program <a
href="../html/man/grdraster.html" ><span
class="phvb8t-">grdraster</span></a><a
id="dx1-9011"></a> to extract subsets of global gridded
data sets. For your convenience we also supply the subsets in the event you do not wish to install
<a
href="../html/man/grdraster.html" ><span
class="phvb8t-">grdraster</span></a><a
id="dx1-9012"></a> and the public data sets it can read. Thus, run the <a
href="../html/man/grdraster.html" ><span
class="phvb8t-">grdraster</span></a><a
id="dx1-9013"></a> commands if you have made
the installation or ignore them if you have not.
</li>
<li
class="enumerate" id="x1-9015x6">For all but the simplest <a
href="http://gmt.soest.hawaii.edu" ><span
class="ptmb8t-">GMT</span></a> jobs it is recommended that you place all the <a
href="http://gmt.soest.hawaii.edu" ><span
class="ptmb8t-">GMT</span></a> (and <span
class="ptmri8t-">UNIX</span>)
commands in a shell script file and make it executable. To ensure that <span
class="ptmri8t-">UNIX</span> recognizes your script as
a shell script it is a good habit always to start the script with the line #!/bin/sh or #!/bin/csh, depending
on the shell you prefer to use. All the examples in this tutorial assumes you are running the Bourne
shell, <span
class="ptmbo8t-">sh</span><a
id="dx1-9016"></a>; if you are using something different then you are on your own.
</li>
<li
class="enumerate" id="x1-9018x7">Making a script executable is accomplished using the <span
class="pcrr8t-">chmod </span>command, e.g., the script <span class="underline">figure_1.sh</span> is
made executable with “<span
class="pcrr8t-">chmod +x figure_1.sh</span>”.
</li>
<li
class="enumerate" id="x1-9020x8">To view a <span
class="ptmri8t-">PostScript</span> file (e.g., <span class="underline">map.ps</span>) on a UNIX workstation we use <span
class="ptmbo8t-">gv</span><a
id="dx1-9021"></a> <span class="underline">map.ps</span>. On some systems
there will be similar commands, like <span class="underline">imagetool</span> and <span class="underline">pageview</span> on Sun workstations. In this text we will
refer to <span
class="ptmbo8t-">gv</span><a
id="dx1-9022"></a>; please substitute the relevant <span
class="ptmri8t-">PostScript</span> previewer on your system.
</li>
<li
class="enumerate" id="x1-9024x9">Please cd into the directory <span class="underline">tutorial</span>. We are now ready to start.
</li></ol>
<!--l. 167--><p class="noindent" >
</p>
<h3 class="sectionHead"><span class="titlemark">1.2 </span> <a
id="x1-100001.2"></a>The <a
href="http://gmt.soest.hawaii.edu" ><span
class="ptmb8t-">GMT</span></a> environment: What happens when you run <a
href="http://gmt.soest.hawaii.edu" ><span
class="ptmb8t-">GMT</span></a>?</h3>
<a
id="dx1-10001"></a>
<a
id="dx1-10002"></a>
<!--l. 171--><p class="noindent" >To get a good grasp on <a
href="http://gmt.soest.hawaii.edu" ><span
class="ptmb8t-">GMT</span></a> one must understand what is going on “under the hood”. Figure <a
href="#x1-10003r1">1.1<!--tex4ht:ref: fig:GMT_Environment --></a> illustrates the
relationships you need to be aware of at run-time.
</p>
<hr class="figure" /><div class="figure"
>
<a
id="x1-10003r1"></a>
<!--l. 176--><p class="noindent" ><img
src="images/GMT_Environment.png" alt="PIC"
/>
<br /> </p><div class="caption"
><span class="id">Figure 1.1: </span><span
class="content">The <a
href="http://gmt.soest.hawaii.edu" ><span
class="ptmb8t-">GMT</span></a> run-time environment.</span></div><!--tex4ht:label?: x1-10003r1 -->
</div><hr class="endfigure" />
<h4 class="subsectionHead"><span class="titlemark">1.2.1 </span> <a
id="x1-110001.2.1"></a>Input data</h4>
<!--l. 182--><p class="noindent" >A <a
href="http://gmt.soest.hawaii.edu" ><span
class="ptmb8t-">GMT</span></a> program may or may not take input files. Three different types of input are recognized (more details can
be found in Appendix B in the Technical Reference): <a
id="dx1-11001"></a><a
id="dx1-11002"></a>
</p><!--l. 188--><p class="indent" >
</p><ol class="enumerate1" >
<li
class="enumerate" id="x1-11004x1">Data tables. These are “spreadsheet” tables with a fixed number of columns and unlimited number of
rows. We distinguish between two groups:
<ul class="itemize1">
<li class="itemize">ASCII (Preferred unless files are huge)
<dl class="description"><dt class="description">
<span
class="ptmb8t-">–</span> </dt><dd
class="description">Single segment [Default]
</dd><dt class="description">
<span
class="ptmb8t-">–</span> </dt><dd
class="description">Multi-segment with internal header records (<span
class="ptmb8t-">–M</span>)</dd></dl>
</li>
<li class="itemize">Binary (to speed up input/output)
<dl class="description"><dt class="description">
<span
class="ptmb8t-">–</span> </dt><dd
class="description">Single segment [Default]
</dd><dt class="description">
<span
class="ptmb8t-">–</span> </dt><dd
class="description">Multi-segment (segment headers are all NaN fields) (<span
class="ptmb8t-">–M</span>)</dd></dl>
</li></ul>
</li>
<li
class="enumerate" id="x1-11006x2">Gridded dated sets. These are data matrices (evenly spaced in two coordinates) that come in two
flavors:
<ul class="itemize1">
<li class="itemize">Grid-line registration
</li>
<li class="itemize">Pixel registration
</li></ul>
<!--l. 228--><p class="noindent" >You may choose among several file formats (even define your own format), but the <a
href="http://gmt.soest.hawaii.edu" ><span
class="ptmb8t-">GMT</span></a> default is the
architecture-indenpendent netCDF format.
</p></li>
<li
class="enumerate" id="x1-11008x3">Color palette table (For imaging, color plots, and contour maps). We will discuss these later.
</li></ol>
<!--l. 236--><p class="noindent" >
</p>
<h4 class="subsectionHead"><span class="titlemark">1.2.2 </span> <a
id="x1-120001.2.2"></a>Job Control</h4>
<!--l. 238--><p class="noindent" ><a
href="http://gmt.soest.hawaii.edu" ><span
class="ptmb8t-">GMT</span></a> programs may get operational parameters from several places:
</p><!--l. 240--><p class="indent" >
</p><ol class="enumerate1" >
<li
class="enumerate" id="x1-12002x1">Supplied command line options/switches or program defaults.
</li>
<li
class="enumerate" id="x1-12004x2">Short-hand notation to select previously used option arguments (stored in <span class="underline">.gmtcommands4</span>). <a
id="dx1-12005"></a>
</li>
<li
class="enumerate" id="x1-12007x3">Implicitly using <a
href="http://gmt.soest.hawaii.edu" ><span
class="ptmb8t-">GMT</span></a> defaults for a variety of parameters (stored in <span class="underline">.gmtdefaults4</span>).
</li>
<li
class="enumerate" id="x1-12009x4">May use hidden support data like coastlines or <span
class="ptmri8t-">PostScript</span> patterns.
</li></ol>
<!--l. 255--><p class="noindent" >
</p>
<h4 class="subsectionHead"><span class="titlemark">1.2.3 </span> <a
id="x1-130001.2.3"></a>Output data</h4>
<!--l. 256--><p class="noindent" >There are 6 general categories of output produced by <a
href="http://gmt.soest.hawaii.edu" ><span
class="ptmb8t-">GMT</span></a>:
</p><!--l. 258--><p class="indent" >
</p><ol class="enumerate1" >
<li
class="enumerate" id="x1-13002x1"><span
class="ptmri8t-">PostScript</span> plot commands.
</li>
<li
class="enumerate" id="x1-13004x2">Data Table(s).
</li>
<li
class="enumerate" id="x1-13006x3">Gridded data set(s).
</li>
<li
class="enumerate" id="x1-13008x4">Statistics & Summaries.
</li>
<li
class="enumerate" id="x1-13010x5">Warnings and Errors, written to <span
class="ptmri8t-">stderr</span>.
</li>
<li
class="enumerate" id="x1-13012x6">Exit status (0 means success, otherwise failure).
</li></ol>
<!--l. 274--><p class="indent" > Note: <a
href="http://gmt.soest.hawaii.edu" ><span
class="ptmb8t-">GMT</span></a> automatically creates and updates a history of past <a
href="http://gmt.soest.hawaii.edu" ><span
class="ptmb8t-">GMT</span></a> command options for the common
switches. This history file is called <span class="underline">.gmtcommands</span> and one will be created in every directory from which
<a
href="http://gmt.soest.hawaii.edu" ><span
class="ptmb8t-">GMT</span></a> programs are executed. Many initial problems with <a
href="http://gmt.soest.hawaii.edu" ><span
class="ptmb8t-">GMT</span></a> usage result from not fully appreciating the
relationships shown in Figure <a
href="#x1-10003r1">1.1<!--tex4ht:ref: fig:GMT_Environment --></a>.
</p><!--l. 281--><p class="noindent" >
</p>
<h3 class="sectionHead"><span class="titlemark">1.3 </span> <a
id="x1-140001.3"></a>The UNIX Environment: Entry Level Knowledge</h3>
<!--l. 283--><p class="noindent" >
</p>
<h4 class="subsectionHead"><span class="titlemark">1.3.1 </span> <a
id="x1-150001.3.1"></a>Redirection</h4>
<a
id="dx1-15001"></a>
<a
id="dx1-15002"></a>
<!--l. 287--><p class="noindent" >Most <a
href="http://gmt.soest.hawaii.edu" ><span
class="ptmb8t-">GMT</span></a> programs read their input from the terminal (called <span
class="ptmri8t-">stdin</span>) or from files, and write their output to the
terminal (called <span
class="ptmri8t-">stdout</span>). To use files instead one can use <span
class="ptmri8t-">UNIX</span> redirection:
</p>
<div class="verbatim" id="verbatim-1">
GMTprogram input-file > output-file
 <br />GMTprogram < input-file > output-file
 <br />GMTprogram input-file >> output-file       # Append to existing file
</div>
<!--l. 296--><p class="nopar" >
</p><!--l. 299--><p class="noindent" >In this example, and in all those to follow, it is assumed that you do not have the shell variable <span
class="ptmb8t-">noclobber </span>set. If
you do, it prevents accidental overwriting of existing files. That may be a noble cause, but it is extremely annoying.
So please, <span
class="ptmb8t-">unset noclobber</span>.
</p><!--l. 304--><p class="noindent" >
</p>
<h4 class="subsectionHead"><span class="titlemark">1.3.2 </span> <a
id="x1-160001.3.2"></a>Piping (<!--l. 304--><math
xmlns="http://www.w3.org/1998/Math/MathML"
display="inline" ><mo
class="MathClass-rel">|</mo></math>)</h4>
<a
id="dx1-16001"></a>
<a
id="dx1-16002"></a>
<!--l. 308--><p class="noindent" >Sometimes we want to use the output from one program as input to another program. This is achieved with
<span
class="ptmri8t-">UNIX</span> pipes:
</p>
<div class="verbatim" id="verbatim-2">
Someprogram | GMTprogram1 | GMTprogram2 > Output-file (or | lp)
</div>
<!--l. 313--><p class="nopar" >
</p><!--l. 316--><p class="noindent" >
</p>
<h4 class="subsectionHead"><span class="titlemark">1.3.3 </span> <a
id="x1-170001.3.3"></a>Standard error (<span
class="ptmri8t-">stderr</span>)</h4>
<a
id="dx1-17001"></a>
<a
id="dx1-17002"></a>
<!--l. 320--><p class="noindent" >Most <span
class="ptmri8t-">UNIX</span> and <a
href="http://gmt.soest.hawaii.edu" ><span
class="ptmb8t-">GMT</span></a> programs will on occasion write error messages. These are typically written to a separate
data stream called <span
class="ptmri8t-">stderr </span>and can be redirected separately from the standard output (which goes to <span
class="ptmri8t-">stdout</span>). To send
the error messages to the same location as standard output we use
</p>
<div class="verbatim" id="verbatim-3">
UNIXprogram > errors.log 2>&1
</div>
<!--l. 328--><p class="nopar" >
</p><!--l. 331--><p class="indent" > When we want to save both program output and error messages to separate files we use the following
syntax:
</p>
<div class="verbatim" id="verbatim-4">
GMTprogram > output.d 2> errors.log
</div>
<!--l. 336--><p class="nopar" >
</p><!--l. 339--><p class="noindent" >
</p>
<h4 class="subsectionHead"><span class="titlemark">1.3.4 </span> <a
id="x1-180001.3.4"></a>File name expansion or “wild cards”</h4>
<a
id="dx1-18001"></a>
<a
id="dx1-18002"></a>
<!--l. 343--><p class="noindent" ><span
class="ptmri8t-">UNIX</span> provides several ways to select groups of files based on name patterns (Table <a
href="#x1-18003r1">1.1<!--tex4ht:ref: tbl:wildcard --></a>):
</p>
<div class="table">
<!--l. 346--><p class="indent" > <a
id="x1-18003r1"></a></p><hr class="float" /><div class="float"
>
<div class="tabular"> <table id="TBL-1" class="tabular"
cellspacing="0" cellpadding="0" rules="groups"
><colgroup id="TBL-1-1g"><col
id="TBL-1-1" /></colgroup><colgroup id="TBL-1-2g"><col
id="TBL-1-2" /></colgroup><tr
class="hline"><td><hr /></td><td><hr /></td></tr><tr
style="vertical-align:baseline;" id="TBL-1-1-"><td style="text-align:center; white-space:nowrap;" id="TBL-1-1-1"
class="td11"> <div class="multicolumn" style="text-align:center; white-space:nowrap;"><span
class="ptmri8t-x-x-90">Code</span></div> </td><td style="text-align:center; white-space:nowrap;" id="TBL-1-1-2"
class="td11"> <div class="multicolumn" style="text-align:center; white-space:nowrap;"><span
class="ptmri8t-x-x-90">Meaning</span></div>
</td></tr><tr
class="hline"><td><hr /></td><td><hr /></td></tr><tr
style="vertical-align:baseline;" id="TBL-1-2-"><td style="text-align:left; white-space:nowrap;" id="TBL-1-2-1"
class="td11"><span
class="ptmr8t-x-x-90">* </span></td><td style="text-align:left; white-space:nowrap;" id="TBL-1-2-2"
class="td11"><span
class="ptmr8t-x-x-90">Matches anything </span></td>
</tr><tr
class="hline"><td><hr /></td><td><hr /></td></tr><tr
style="vertical-align:baseline;" id="TBL-1-3-"><td style="text-align:left; white-space:nowrap;" id="TBL-1-3-1"
class="td11"><span
class="ptmr8t-x-x-90">? </span></td><td style="text-align:left; white-space:nowrap;" id="TBL-1-3-2"
class="td11"><span
class="ptmr8t-x-x-90">Matches any single character </span></td>
</tr><tr
class="hline"><td><hr /></td><td><hr /></td></tr><tr
style="vertical-align:baseline;" id="TBL-1-4-"><td style="text-align:left; white-space:nowrap;" id="TBL-1-4-1"
class="td11"><span
class="ptmr8t-x-x-90">[</span><span
class="ptmri8t-x-x-90">list</span><span
class="ptmr8t-x-x-90">] </span></td><td style="text-align:left; white-space:nowrap;" id="TBL-1-4-2"
class="td11"><span
class="ptmr8t-x-x-90">Matches characters in the list </span></td>
</tr><tr
class="hline"><td><hr /></td><td><hr /></td></tr><tr
style="vertical-align:baseline;" id="TBL-1-5-"><td style="text-align:left; white-space:nowrap;" id="TBL-1-5-1"
class="td11"><span
class="ptmr8t-x-x-90">[</span><span
class="ptmri8t-x-x-90">range</span><span
class="ptmr8t-x-x-90">]</span></td><td style="text-align:left; white-space:nowrap;" id="TBL-1-5-2"
class="td11"><span
class="ptmr8t-x-x-90">Matches characters in the given range</span></td>
</tr><tr
class="hline"><td><hr /></td><td><hr /></td></tr><tr
style="vertical-align:baseline;" id="TBL-1-6-"><td style="text-align:left; white-space:nowrap;" id="TBL-1-6-1"
class="td11"> </td></tr></table></div>
<br /><div class="caption"
><span class="id">Table 1.1: </span><span
class="content"><span
class="ptmri8t-">UNIX</span> wildcards.</span></div><!--tex4ht:label?: x1-18003r1 -->
</div><hr class="endfloat" />
</div>
<!--l. 359--><p class="noindent" >You can save much time by getting into the habit of selecting “good” filenames that make it easy to select subsets
of all files using the <span
class="ptmri8t-">UNIX</span> wild card notation.
</p>
<h5 class="subsubsectionHead"><a
id="x1-190001.3.4"></a>Examples</h5>
<a
id="dx1-19001"></a>
<ul class="itemize1">
<li class="itemize">GMTprogram data_*.d operates on all files starting with “data_” and ending in “.d”.
</li>
<li class="itemize">GMTprogram line_?.d works on all files starting with “line_” followed by any single character and
ending in “.d”.
</li>
<li class="itemize">GMTprogram section_1[0-9]0.part_[12] only processes data from sections 100 through 190, only using
every 10th profile, and gets both part 1 and 2.
</li></ul>
<a
id="dx1-19002"></a>
<!--l. 381--><p class="noindent" >
</p>
<h3 class="sectionHead"><span class="titlemark">1.4 </span> <a
id="x1-200001.4"></a>Laboratory Exercises</h3>
<!--l. 383--><p class="noindent" >We will begin our adventure by making some simple plot axes and coastline basemaps. We will do this in order to
introduce the all-important <span
class="pcrb8t-">-B</span>, <span
class="pcrb8t-">-J</span>, and <span
class="pcrb8t-">-R </span>switches and to familiarize ourselves with a few selected
<a
href="http://gmt.soest.hawaii.edu" ><span
class="ptmb8t-">GMT</span></a> projections. The <a
href="http://gmt.soest.hawaii.edu" ><span
class="ptmb8t-">GMT</span></a> programs we will utilize are <a
href="../html/man/psbasemap.html" ><span
class="phvb8t-">psbasemap</span></a><a
id="dx1-20001"></a> and <a
href="../html/man/pscoast.html" ><span
class="phvb8t-">pscoast</span></a><a
id="dx1-20002"></a>. Please consult their
manual pages on the <a
href="http://gmt.soest.hawaii.edu" ><span
class="ptmb8t-">GMT</span></a> web site for reference.
</p><!--l. 390--><p class="noindent" >
</p>
<h4 class="subsectionHead"><span class="titlemark">1.4.1 </span> <a
id="x1-210001.4.1"></a>Linear projection</h4>
<a
id="dx1-21001"></a>
<a
id="dx1-21002"></a>
<!--l. 394--><p class="noindent" >We start by making the basemap frame for a linear <span
class="ptmri8t-">x-y </span>plot. We want it to go from 10 to 70 in <span
class="ptmri8t-">x</span>, annotating every
10, and from -3 to 8 in <span
class="ptmri8t-">y</span>, annotating every 1. The final plot should be 4 by 3 inches in size. Here’s how we do
it:
</p>
<div class="verbatim" id="verbatim-5">
psbasemap -R10/70/-3/8 -JX4i/3i -B10/1:.~My first plot~: -P > plot.ps
</div>
<!--l. 401--><p class="nopar" >
</p><!--l. 404--><p class="noindent" >You can view the result with <span
class="ptmbo8t-">gv</span><a
id="dx1-21003"></a> <span class="underline">plot.ps</span>.
</p><!--l. 407--><p class="noindent" >
</p>
<h5 class="subsubsectionHead"><a
id="x1-220001.4.1"></a>Exercises</h5>
<a
id="dx1-22001"></a>
<!--l. 410--><p class="noindent" >
</p><ol class="enumerate1" >
<li
class="enumerate" id="x1-22003x1">Try change the <span
class="pcrb8t-">-JX </span>values.
</li>
<li
class="enumerate" id="x1-22005x2">Try change the <span
class="pcrb8t-">-B </span>values.
</li>
<li
class="enumerate" id="x1-22007x3">Omit the <span
class="pcrb8t-">-P</span>.
</li></ol>
<a
id="dx1-22008"></a>
<!--l. 421--><p class="noindent" >
</p>
<h4 class="subsectionHead"><span class="titlemark">1.4.2 </span> <a
id="x1-230001.4.2"></a>Logarithmic projection</h4>
<a
id="dx1-23001"></a>
<a
id="dx1-23002"></a>
<!--l. 425--><p class="noindent" >We next will show how to do a basemap for a log–log plot. We will assume that the raw <span
class="ptmri8t-">x </span>data range from 3 to 9613 and <span
class="ptmri8t-">y</span>
ranges from <!--l. 427--><math
xmlns="http://www.w3.org/1998/Math/MathML"
display="inline" ><mn>3</mn><mo
class="MathClass-punc">.</mo><mn>2</mn><mo
class="MathClass-bin">⋅</mo><mn>1</mn><msup><mrow
><mn>0</mn></mrow><mrow
><mn>2</mn><mn>0</mn></mrow></msup
></math>
to <!--l. 427--><math
xmlns="http://www.w3.org/1998/Math/MathML"
display="inline" ><mn>6</mn><mo
class="MathClass-punc">.</mo><mn>8</mn><mo
class="MathClass-bin">⋅</mo><mn>1</mn><msup><mrow
><mn>0</mn></mrow><mrow
><mn>2</mn><mn>4</mn></mrow></msup
></math>. One
possibility is
</p>
<div class="verbatim" id="verbatim-6">
psbasemap -R1/10000/1e20/1e25 -JX9il/6il \
 <br />   -B2:~Wavelength (m)~:/a1pf3:~Power (W)~:WS > plot.ps
</div>
<!--l. 432--><p class="nopar" >
</p><!--l. 435--><p class="noindent" >(The backslash <!--l. 436--><math
xmlns="http://www.w3.org/1998/Math/MathML"
display="inline" ><mo
class="MathClass-bin">\</mo></math>
makes <span
class="ptmri8t-">UNIX</span> ignore the carriage return that follows and treat the two lines as one long command).
</p><!--l. 438--><p class="noindent" >
</p>
<h5 class="subsubsectionHead"><a
id="x1-240001.4.2"></a>Exercises</h5>
<a
id="dx1-24001"></a>
<!--l. 441--><p class="noindent" >
</p><ol class="enumerate1" >
<li
class="enumerate" id="x1-24003x1">Do not append <span
class="ptmb8t-">l </span>to the axes lengths.
</li>
<li
class="enumerate" id="x1-24005x2">Leave the <span
class="ptmb8t-">p </span>modifier out of the <span
class="pcrb8t-">-B </span>string.
</li>
<li
class="enumerate" id="x1-24007x3">Add <span
class="ptmb8t-">g</span>3 to each side of the slash in <span
class="pcrb8t-">-B</span>.
</li></ol>
<a
id="dx1-24008"></a>
<!--l. 452--><p class="noindent" >
</p>
<h4 class="subsectionHead"><span class="titlemark">1.4.3 </span> <a
id="x1-250001.4.3"></a>Mercator projection</h4>
<a
id="dx1-25001"></a>
<a
id="dx1-25002"></a>
<!--l. 456--><p class="noindent" >Despite the problems of extreme horizontal exaggeration at high latitudes, the conformal Mercator projection
(<span
class="pcrb8t-">-JM</span>) remains the stalwart of location maps used by scientists. It is one of several cylindrical projections offered
by <a
href="http://gmt.soest.hawaii.edu" ><span
class="ptmb8t-">GMT</span></a>; here we will only have time to focus on one such projection. The complete syntax is simply
<br
class="newline" />
</p><!--l. 463--><p class="indent" > <span
class="pcrb8t-">-JM</span><span
class="ptmri8t-">width </span><br
class="newline" />
</p><!--l. 465--><p class="indent" > To make coastline maps we use <a
href="../html/man/pscoast.html" ><span
class="phvb8t-">pscoast</span></a><a
id="dx1-25003"></a> which automatically will access the <a
href="http://gmt.soest.hawaii.edu" ><span
class="ptmb8t-">GMT</span></a> coastline, river and border data base derived
from the GSHHG database<span class="footnote-mark"><a
href="#fn1x1" id="fn1x1-bk"><sup class="textsuperscript">1</sup></a></span><a
id="x1-25004f1"></a>.
In addition to the common switches we may need to use some of several <a
href="../html/man/pscoast.html" ><span
class="phvb8t-">pscoast</span></a><a
id="dx1-25005"></a> -specific options (see
Table <a
href="#x1-25006r2">1.2<!--tex4ht:ref: tbl:pscoast --></a>).
</p>
<div class="table">
<!--l. 471--><p class="indent" > <a
id="x1-25006r2"></a></p><hr class="float" /><div class="float"
>
<div class="tabular"> <table id="TBL-2" class="tabular"
cellspacing="0" cellpadding="0" rules="groups"
><colgroup id="TBL-2-1g"><col
id="TBL-2-1" /></colgroup><colgroup id="TBL-2-2g"><col
id="TBL-2-2" /></colgroup><tr
class="hline"><td><hr /></td><td><hr /></td></tr><tr
style="vertical-align:baseline;" id="TBL-2-1-"><td style="text-align:center; white-space:nowrap;" id="TBL-2-1-1"
class="td11"><div class="multicolumn" style="text-align:center; white-space:nowrap;"><span
class="ptmri8t-x-x-90">Option</span></div></td><td style="text-align:center; white-space:nowrap;" id="TBL-2-1-2"
class="td11"> <div class="multicolumn" style="text-align:center; white-space:nowrap;"><span
class="ptmri8t-x-x-90">Purpose</span></div>
</td></tr><tr
class="hline"><td><hr /></td><td><hr /></td></tr><tr
style="vertical-align:baseline;" id="TBL-2-2-"><td style="text-align:left; white-space:nowrap;" id="TBL-2-2-1"
class="td11"><span
class="pcrb8t-x-x-90">-A </span></td><td style="text-align:left; white-space:nowrap;" id="TBL-2-2-2"
class="td11"><span
class="ptmr8t-x-x-90">Exclude small features or those of high hierarchical levels (see Appendix K)</span></td>
</tr><tr
class="hline"><td><hr /></td><td><hr /></td></tr><tr
style="vertical-align:baseline;" id="TBL-2-3-"><td style="text-align:left; white-space:nowrap;" id="TBL-2-3-1"
class="td11"><span
class="pcrb8t-x-x-90">-D </span></td><td style="text-align:left; white-space:nowrap;" id="TBL-2-3-2"
class="td11"><span
class="ptmr8t-x-x-90">Select data resolution (</span><span
class="ptmb8t-x-x-90">f</span><span
class="ptmr8t-x-x-90">ull, </span><span
class="ptmb8t-x-x-90">h</span><span
class="ptmr8t-x-x-90">igh, </span><span
class="ptmb8t-x-x-90">i</span><span
class="ptmr8t-x-x-90">ntermediate, </span><span
class="ptmb8t-x-x-90">l</span><span
class="ptmr8t-x-x-90">ow, or </span><span
class="ptmb8t-x-x-90">c</span><span
class="ptmr8t-x-x-90">rude) </span></td>
</tr><tr
class="hline"><td><hr /></td><td><hr /></td></tr><tr
style="vertical-align:baseline;" id="TBL-2-4-"><td style="text-align:left; white-space:nowrap;" id="TBL-2-4-1"
class="td11"><span
class="pcrb8t-x-x-90">-G </span></td><td style="text-align:left; white-space:nowrap;" id="TBL-2-4-2"
class="td11"><span
class="ptmr8t-x-x-90">Set color of dry areas (default does not paint) </span></td>
</tr><tr
class="hline"><td><hr /></td><td><hr /></td></tr><tr
style="vertical-align:baseline;" id="TBL-2-5-"><td style="text-align:left; white-space:nowrap;" id="TBL-2-5-1"
class="td11"><span
class="pcrb8t-x-x-90">-I </span></td><td style="text-align:left; white-space:nowrap;" id="TBL-2-5-2"
class="td11"><span
class="ptmr8t-x-x-90">Draw rivers (chose features from one or more hierarchical categories) </span></td>
</tr><tr
class="hline"><td><hr /></td><td><hr /></td></tr><tr
style="vertical-align:baseline;" id="TBL-2-6-"><td style="text-align:left; white-space:nowrap;" id="TBL-2-6-1"
class="td11"><span
class="pcrb8t-x-x-90">-L </span></td><td style="text-align:left; white-space:nowrap;" id="TBL-2-6-2"
class="td11"><span
class="ptmr8t-x-x-90">Plot map scale (length scale can be km, miles, or nautical miles) </span></td>
</tr><tr
class="hline"><td><hr /></td><td><hr /></td></tr><tr
style="vertical-align:baseline;" id="TBL-2-7-"><td style="text-align:left; white-space:nowrap;" id="TBL-2-7-1"
class="td11"><span
class="pcrb8t-x-x-90">-N </span></td><td style="text-align:left; white-space:nowrap;" id="TBL-2-7-2"
class="td11"><span
class="ptmr8t-x-x-90">Draw political borders (including US state borders) </span></td>
</tr><tr
class="hline"><td><hr /></td><td><hr /></td></tr><tr
style="vertical-align:baseline;" id="TBL-2-8-"><td style="text-align:left; white-space:nowrap;" id="TBL-2-8-1"
class="td11"><span
class="pcrb8t-x-x-90">-S </span></td><td style="text-align:left; white-space:nowrap;" id="TBL-2-8-2"
class="td11"><span
class="ptmr8t-x-x-90">Set color for wet areas (default does not paint) </span></td>
</tr><tr
class="hline"><td><hr /></td><td><hr /></td></tr><tr
style="vertical-align:baseline;" id="TBL-2-9-"><td style="text-align:left; white-space:nowrap;" id="TBL-2-9-1"
class="td11"><span
class="pcrb8t-x-x-90">-W </span></td><td style="text-align:left; white-space:nowrap;" id="TBL-2-9-2"
class="td11"><span
class="ptmr8t-x-x-90">Draw coastlines and set pen thickness </span></td>
</tr><tr
class="hline"><td><hr /></td><td><hr /></td></tr><tr
style="vertical-align:baseline;" id="TBL-2-10-"><td style="text-align:left; white-space:nowrap;" id="TBL-2-10-1"
class="td11"> </td></tr></table></div>
<br /><div class="caption"
><span class="id">Table 1.2: </span><span
class="content">Main options when making coastline plots or overlays.</span></div><!--tex4ht:label?: x1-25006r2 -->
</div><hr class="endfloat" />
</div>
<!--l. 488--><p class="indent" > One of <span
class="pcrb8t-">-W</span>, <span
class="pcrb8t-">-G</span>, <span
class="pcrb8t-">-S </span>must be selected. Our first coastline example is from Latin America:
</p>
<div class="verbatim" id="verbatim-7">
pscoast -R-90/-70/0/20 -JM6i -P -B5g5 -Gchocolate > map.ps
</div>
<!--l. 493--><p class="nopar" >
</p>
<h5 class="subsubsectionHead"><a
id="x1-260001.4.3"></a>Exercises</h5>
<a
id="dx1-26001"></a>
<!--l. 499--><p class="noindent" >
</p><ol class="enumerate1" >
<li
class="enumerate" id="x1-26003x1">Add the <span
class="pcrb8t-">-V </span>option.
</li>
<li
class="enumerate" id="x1-26005x2">Try <span
class="pcrb8t-">-R</span>270/290/0/20 instead. What happens to the annotations?
</li>
<li
class="enumerate" id="x1-26007x3">Edit your <span class="underline">.gmtdefaults4</span> file, change <span
class="ptmb8t-">PLOT_DEGREE_FORMAT </span>to another setting (see the
<a
href="../html/man/gmtdefaults.html" ><span
class="phvb8t-">gmtdefaults</span></a><a
id="dx1-26008"></a> man page), and plot again.
</li>
<li
class="enumerate" id="x1-26010x4">Pick another region and change land color.
</li>
<li
class="enumerate" id="x1-26012x5">Pick a region that includes the north or south poles.
</li>
<li
class="enumerate" id="x1-26014x6">Try <span
class="pcrb8t-">-W</span>0.25<span
class="ptmb8t-">p </span>instead of (or in addition to) <span
class="pcrb8t-">-G</span>.
</li></ol>
<a
id="dx1-26015"></a>
<!--l. 517--><p class="noindent" >
</p>
<h4 class="subsectionHead"><span class="titlemark">1.4.4 </span> <a
id="x1-270001.4.4"></a>Albers projection</h4>
<a
id="dx1-27001"></a>
<a
id="dx1-27002"></a>
<!--l. 521--><p class="noindent" >The Albers projection (<span
class="pcrb8t-">-JB</span>) is an equal-area conical projection; its conformal cousin is the Lambert conic
projection (<span
class="pcrb8t-">-JL</span>). Their usages are almost identical so we will only use the Albers here. The general syntax is
<br
class="newline" />
</p><!--l. 526--><p class="indent" > <span
class="pcrb8t-">-JB</span><!--l. 526--><math
xmlns="http://www.w3.org/1998/Math/MathML"
display="inline" ><mi
>l</mi><mi
>o</mi><msub><mrow
><mi
>n</mi></mrow><mrow
><mn>0</mn></mrow></msub
><mo
class="MathClass-bin">∕</mo><mi
>l</mi><mi
>a</mi><msub><mrow
><mi
>t</mi></mrow><mrow
><mn>0</mn></mrow></msub
><mo
class="MathClass-bin">∕</mo><mi
>l</mi><mi
>a</mi><msub><mrow
><mi
>t</mi></mrow><mrow
><mn>1</mn></mrow></msub
><mo
class="MathClass-bin">∕</mo><mi
>l</mi><mi
>a</mi><msub><mrow
><mi
>t</mi></mrow><mrow
><mn>2</mn></mrow></msub
><mo
class="MathClass-bin">∕</mo><mi
>w</mi><mi
>i</mi><mi
>d</mi><mi
>t</mi><mi
>h</mi></math>
<br
class="newline" />
</p><!--l. 528--><p class="noindent" >where (<!--l. 529--><math
xmlns="http://www.w3.org/1998/Math/MathML"
display="inline" ><mi
>l</mi><mi
>o</mi><msub><mrow
><mi
>n</mi></mrow><mrow
><mn>0</mn></mrow></msub
><mo
class="MathClass-punc">,</mo><mi
>l</mi><mi
>a</mi><msub><mrow
><mi
>t</mi></mrow><mrow
><mn>0</mn></mrow></msub
></math>) is the map
(projection) center and <!--l. 529--><math
xmlns="http://www.w3.org/1998/Math/MathML"
display="inline" ><mi
>l</mi><mi
>a</mi><msub><mrow
><mi
>t</mi></mrow><mrow
><mn>1</mn></mrow></msub
><mo
class="MathClass-punc">,</mo><mi
>l</mi><mi
>a</mi><msub><mrow
><mi
>t</mi></mrow><mrow
><mn>2</mn></mrow></msub
></math>
are the two standard parallels where the cone intersects the Earth’s surface. We try the following
command:
</p>
<div class="verbatim" id="verbatim-8">
pscoast -R-130/-70/24/52 -JB-100/35/33/45/6i -B10g5:.~Conic Projection~: \
 <br />   -N1/thickest -N2/thinnest -A500 -Ggray -Wthinnest -P > map.ps
</div>
<!--l. 536--><p class="nopar" >
</p><!--l. 539--><p class="noindent" >
</p>
<h5 class="subsubsectionHead"><a
id="x1-280001.4.4"></a>Exercises</h5>
<a
id="dx1-28001"></a>
<!--l. 542--><p class="noindent" >
</p><ol class="enumerate1" >
<li
class="enumerate" id="x1-28003x1">Change the parameter <span
class="ptmb8t-">GRID_CROSS_SIZE_PRIMARY </span>to make grid crosses instead of gridlines.
</li>
<li
class="enumerate" id="x1-28005x2">Change <span
class="pcrb8t-">-R </span>to a rectangular box specification instead of minimum and maximum values.
</li></ol>
<a
id="dx1-28006"></a>
<!--l. 552--><p class="noindent" >
</p>
<h4 class="subsectionHead"><span class="titlemark">1.4.5 </span> <a
id="x1-290001.4.5"></a>Orthographic projection</h4>
<a
id="dx1-29001"></a>
<a
id="dx1-29002"></a>
<!--l. 556--><p class="noindent" >The azimuthal orthographic projection (<span
class="pcrb8t-">-JG</span>) is one of several projections with similar syntax and behavior; the
one we have chosen mimics viewing the Earth from space at an infinite distance; it is neither conformal nor
equal-area. The syntax for this projection is <br
class="newline" />
</p><!--l. 562--><p class="indent" > <span
class="pcrb8t-">-JG</span><!--l. 562--><math
xmlns="http://www.w3.org/1998/Math/MathML"
display="inline" ><mi
>l</mi><mi
>o</mi><msub><mrow
><mi
>n</mi></mrow><mrow
><mn>0</mn></mrow></msub
><mo
class="MathClass-bin">∕</mo><mi
>l</mi><mi
>a</mi><msub><mrow
><mi
>t</mi></mrow><mrow
><mn>0</mn></mrow></msub
><mo
class="MathClass-bin">∕</mo><mi
>w</mi><mi
>i</mi><mi
>d</mi><mi
>t</mi><mi
>h</mi></math>
<br
class="newline" />
</p><!--l. 564--><p class="noindent" >where (<!--l. 565--><math
xmlns="http://www.w3.org/1998/Math/MathML"
display="inline" ><mi
>l</mi><mi
>o</mi><msub><mrow
><mi
>n</mi></mrow><mrow
><mn>0</mn></mrow></msub
><mo
class="MathClass-punc">,</mo><mi
>l</mi><mi
>a</mi><msub><mrow
><mi
>t</mi></mrow><mrow
><mn>0</mn></mrow></msub
></math>)
is the center of the map (projection). As an example we will try
</p>
<div class="verbatim" id="verbatim-9">
pscoast -R0/360/-90/90 -JG280/30/6i -Bg30/g15 -Dc -A5000 -Gwhite \
 <br />    -SDarkTurquoise -P > map.ps
</div>
<!--l. 571--><p class="nopar" >
</p><!--l. 574--><p class="noindent" >
</p>
<h5 class="subsubsectionHead"><a
id="x1-300001.4.5"></a>Exercises</h5>
<a
id="dx1-30001"></a>
<!--l. 577--><p class="noindent" >
</p><ol class="enumerate1" >
<li
class="enumerate" id="x1-30003x1">Use the rectangular option in <span
class="pcrb8t-">-R </span>to make a rectangular map showing the US only.
</li></ol>
<a
id="dx1-30004"></a>
<!--l. 585--><p class="noindent" >
</p>
<h4 class="subsectionHead"><span class="titlemark">1.4.6 </span> <a
id="x1-310001.4.6"></a>Eckert IV and VI projection</h4>
<a
id="dx1-31001"></a>
<a
id="dx1-31002"></a>
<!--l. 589--><p class="noindent" >We conclude the survey of map projections with the Eckert IV and VI projections (<span
class="pcrb8t-">-JK</span>), two of several
projections used for global thematic maps; They are both equal-area projections whose syntax is
<br
class="newline" />
</p><!--l. 593--><p class="indent" >
<span
class="pcrb8t-">-JK</span>[<span
class="ptmb8t-">f</span><!--l. 593--><math
xmlns="http://www.w3.org/1998/Math/MathML"
display="inline" ><mo
class="MathClass-rel">|</mo></math><span
class="ptmb8t-">s</span>]<!--l. 593--><math
xmlns="http://www.w3.org/1998/Math/MathML"
display="inline" ><mi
>l</mi><mi
>o</mi><msub><mrow
><mi
>n</mi></mrow><mrow
><mn>0</mn></mrow></msub
><mo
class="MathClass-bin">∕</mo><mi
>w</mi><mi
>i</mi><mi
>d</mi><mi
>t</mi><mi
>h</mi></math>
<br
class="newline" />
</p><!--l. 595--><p class="noindent" >where <span
class="ptmb8t-">f </span>gives Eckert IV (4) and <span
class="ptmb8t-">s </span>(Default) gives Eckert VI (6). The
<!--l. 597--><math
xmlns="http://www.w3.org/1998/Math/MathML"
display="inline" ><mi
>l</mi><mi
>o</mi><msub><mrow
><mi
>n</mi></mrow><mrow
><mn>0</mn></mrow></msub
></math> is the
central meridian (which takes precedence over the mid-value implied by the <span
class="pcrb8t-">-R </span>setting). A simple Eckert VI world
map is thus generated by
</p>
<div class="verbatim" id="verbatim-10">
pscoast -R0/360/-90/90 -JKs180/9i -B60g30/30g15 -Dc -A5000 \
 <br />    -Gchocolate -SDarkTurquoise -Wthinnest > map.ps
</div>
<!--l. 604--><p class="nopar" >
</p><!--l. 607--><p class="noindent" >
</p>
<h5 class="subsubsectionHead"><a
id="x1-320001.4.6"></a>Exercises</h5>
<a
id="dx1-32001"></a>
<!--l. 610--><p class="noindent" >
</p><ol class="enumerate1" >
<li
class="enumerate" id="x1-32003x1">Center the map on Greenwich.
</li>
<li
class="enumerate" id="x1-32005x2">Add a map scale with <span
class="pcrb8t-">-L</span>.
</li></ol>
<a
id="dx1-32006"></a>
<h2 class="chapterHead"><span class="titlemark">Chapter 2</span><br /><a
id="x1-330002"></a>SESSION TWO</h2>
<h3 class="sectionHead"><span class="titlemark">2.1 </span> <a
id="x1-340002.1"></a>General Information</h3>
<!--l. 624--><p class="noindent" >There are 18 <a
href="http://gmt.soest.hawaii.edu" ><span
class="ptmb8t-">GMT</span></a> programs that directly create (or add overlays to) plots (Table <a
href="#x1-34019r1">2.1<!--tex4ht:ref: tbl:plotprogs --></a>); the remaining 45 are
mostly concerned with data processing. This session will focus on the task of plotting lines, symbols, and text on
maps. We will build on the skills we acquired while familiarizing ourselves with the various <a
href="http://gmt.soest.hawaii.edu" ><span
class="ptmb8t-">GMT</span></a> map
projections as well as how to select a data domain and boundary annotations.
</p>
<div class="table">
<!--l. 632--><p class="indent" > <a
id="x1-34019r1"></a></p><hr class="float" /><div class="float"
>
<div class="tabular"> <table id="TBL-3" class="tabular"
cellspacing="0" cellpadding="0" rules="groups"
><colgroup id="TBL-3-1g"><col
id="TBL-3-1" /></colgroup><colgroup id="TBL-3-2g"><col
id="TBL-3-2" /></colgroup><tr
class="hline"><td><hr /></td><td><hr /></td></tr><tr
style="vertical-align:baseline;" id="TBL-3-1-"><td style="text-align:center; white-space:nowrap;" id="TBL-3-1-1"
class="td11"> <div class="multicolumn" style="text-align:center; white-space:nowrap;"><span
class="ptmri8t-x-x-90">Program</span></div> </td><td style="text-align:center; white-space:nowrap;" id="TBL-3-1-2"
class="td11"> <div class="multicolumn" style="text-align:center; white-space:nowrap;"><span
class="ptmri8t-x-x-90">Purpose</span></div>
</td></tr><tr
class="hline"><td><hr /></td><td><hr /></td></tr><tr
style="vertical-align:baseline;" id="TBL-3-2-"><td colspan="2" style="text-align:center; white-space:nowrap;" id="TBL-3-2-1"
class="td11"> <div class="multicolumn" style="text-align:center; white-space:nowrap;"><span
class="ptmri8t-x-x-90">BASEMAPS</span></div></td></tr><tr
class="hline"><td><hr /></td><td><hr /></td></tr><tr
style="vertical-align:baseline;" id="TBL-3-3-"><td style="text-align:left; white-space:nowrap;" id="TBL-3-3-1"
class="td11"><a
href="../html/man/psbasemap.html" ><span
class="phvb8t-x-x-90">psbasemap</span></a><a
id="dx1-34001"></a> </td><td style="text-align:left; white-space:nowrap;" id="TBL-3-3-2"
class="td11"><span
class="ptmr8t-x-x-90">Create an empty basemap frame with optional scale </span></td>
</tr><tr
class="hline"><td><hr /></td><td><hr /></td></tr><tr
style="vertical-align:baseline;" id="TBL-3-4-"><td style="text-align:left; white-space:nowrap;" id="TBL-3-4-1"
class="td11"><a
href="../html/man/pscoast.html" ><span
class="phvb8t-x-x-90">pscoast</span></a><a
id="dx1-34002"></a> </td><td style="text-align:left; white-space:nowrap;" id="TBL-3-4-2"
class="td11"><span
class="ptmr8t-x-x-90">Plot coastlines, filled continents, rivers, and political borders </span></td>
</tr><tr
class="hline"><td><hr /></td><td><hr /></td></tr><tr
style="vertical-align:baseline;" id="TBL-3-5-"><td style="text-align:left; white-space:nowrap;" id="TBL-3-5-1"
class="td11"><a
href="../html/man/pslegend.html" ><span
class="phvb8t-x-x-90">pslegend</span></a><a
id="dx1-34003"></a> </td><td style="text-align:left; white-space:nowrap;" id="TBL-3-5-2"
class="td11"><span
class="ptmr8t-x-x-90">Create legend overlay </span></td>
</tr><tr
class="hline"><td><hr /></td><td><hr /></td></tr><tr
style="vertical-align:baseline;" id="TBL-3-6-"><td colspan="2" style="text-align:center; white-space:nowrap;" id="TBL-3-6-1"
class="td11"> <div class="multicolumn" style="text-align:center; white-space:nowrap;"><span
class="ptmri8t-x-x-90">POINTS AND LINES</span></div>
</td></tr><tr
class="hline"><td><hr /></td><td><hr /></td></tr><tr
style="vertical-align:baseline;" id="TBL-3-7-"><td style="text-align:left; white-space:nowrap;" id="TBL-3-7-1"
class="td11"><a
href="../html/man/pswiggle.html" ><span
class="phvb8t-x-x-90">pswiggle</span></a><a
id="dx1-34004"></a> </td><td style="text-align:left; white-space:nowrap;" id="TBL-3-7-2"
class="td11"><span
class="ptmr8t-x-x-90">Draw spatial time-series along their </span><!--l. 642--><math
xmlns="http://www.w3.org/1998/Math/MathML"
display="inline" ><mrow ><mo
class="MathClass-open">(</mo><mrow><mi
>x</mi><mo
class="MathClass-punc">,</mo><mi
>y</mi></mrow><mo
class="MathClass-close">)</mo></mrow></math><span
class="ptmr8t-x-x-90">-tracks </span></td>
</tr><tr
class="hline"><td><hr /></td><td><hr /></td></tr><tr
style="vertical-align:baseline;" id="TBL-3-8-"><td style="text-align:left; white-space:nowrap;" id="TBL-3-8-1"
class="td11"><a
href="../html/man/psxy.html" ><span
class="phvb8t-x-x-90">psxy</span></a><a
id="dx1-34005"></a> </td><td style="text-align:left; white-space:nowrap;" id="TBL-3-8-2"
class="td11"><span
class="ptmr8t-x-x-90">Plot symbols, polygons, and lines in 2-D </span></td>
</tr><tr
class="hline"><td><hr /></td><td><hr /></td></tr><tr
style="vertical-align:baseline;" id="TBL-3-9-"><td style="text-align:left; white-space:nowrap;" id="TBL-3-9-1"
class="td11"><a
href="../html/man/psxyz.html" ><span
class="phvb8t-x-x-90">psxyz</span></a><a
id="dx1-34006"></a> </td><td style="text-align:left; white-space:nowrap;" id="TBL-3-9-2"
class="td11"><span
class="ptmr8t-x-x-90">Plot symbols, polygons, and lines in 3-D </span></td>
</tr><tr
class="hline"><td><hr /></td><td><hr /></td></tr><tr
style="vertical-align:baseline;" id="TBL-3-10-"><td colspan="2" style="text-align:center; white-space:nowrap;" id="TBL-3-10-1"
class="td11"> <div class="multicolumn" style="text-align:center; white-space:nowrap;"><span
class="ptmri8t-x-x-90">HISTOGRAMS</span></div></td></tr><tr
class="hline"><td><hr /></td><td><hr /></td></tr><tr
style="vertical-align:baseline;" id="TBL-3-11-"><td style="text-align:left; white-space:nowrap;" id="TBL-3-11-1"
class="td
11"><a
href="../html/man/pshistogram.html" ><span
class="phvb8t-x-x-90">pshistogram</span></a><a
id="dx1-34007"></a></td><td style="text-align:left; white-space:nowrap;" id="TBL-3-11-2"
class="td11"><span
class="ptmr8t-x-x-90">Plot a rectangular histogram </span></td>
</tr><tr
class="hline"><td><hr /></td><td><hr /></td></tr><tr
style="vertical-align:baseline;" id="TBL-3-12-"><td style="text-align:left; white-space:nowrap;" id="TBL-3-12-1"
class="td11"><a
href="../html/man/psrose.html" ><span
class="phvb8t-x-x-90">psrose</span></a><a
id="dx1-34008"></a> </td><td style="text-align:left; white-space:nowrap;" id="TBL-3-12-2"
class="td11"><span
class="ptmr8t-x-x-90">Plot a polar histogram(sector/rose diagram) </span></td>
</tr><tr
class="hline"><td><hr /></td><td><hr /></td></tr><tr
style="vertical-align:baseline;" id="TBL-3-13-"><td colspan="2" style="text-align:center; white-space:nowrap;" id="TBL-3-13-1"
class="td11"> <div class="multicolumn" style="text-align:center; white-space:nowrap;"><span
class="ptmri8t-x-x-90">CONTOURS</span></div>
</td></tr><tr
class="hline"><td><hr /></td><td><hr /></td></tr><tr
style="vertical-align:baseline;" id="TBL-3-14-"><td style="text-align:left; white-space:nowrap;" id="TBL-3-14-1"
class="td11"><a
href="../html/man/grdcontour.html" ><span
class="phvb8t-x-x-90">grdcontour</span></a><a
id="dx1-34009"></a> </td><td style="text-align:left; white-space:nowrap;" id="TBL-3-14-2"
class="td11"><span
class="ptmr8t-x-x-90">Contouring of 2-D gridded data sets </span></td>
</tr><tr
class="hline"><td><hr /></td><td><hr /></td></tr><tr
style="vertical-align:baseline;" id="TBL-3-15-"><td style="text-align:left; white-space:nowrap;" id="TBL-3-15-1"
class="td11"><a
href="../html/man/pscontour.html" ><span
class="phvb8t-x-x-90">pscontour</span></a><a
id="dx1-34010"></a> </td><td style="text-align:left; white-space:nowrap;" id="TBL-3-15-2"
class="td11"><span
class="ptmr8t-x-x-90">Direct contouring or imaging of </span><!--l. 650--><math
xmlns="http://www.w3.org/1998/Math/MathML"
display="inline" ><mi
>x</mi><mi
>y</mi><mi
>z</mi></math> <span
class="ptmr8t-x-x-90">data by optimal triangulation</span></td>
</tr><tr
class="hline"><td><hr /></td><td><hr /></td></tr><tr
style="vertical-align:baseline;" id="TBL-3-16-"><td colspan="2" style="text-align:center; white-space:nowrap;" id="TBL-3-16-1"
class="td11"> <div class="multicolumn" style="text-align:center; white-space:nowrap;"><span
class="ptmri8t-x-x-90">SURFACES</span></div>
</td></tr><tr
class="hline"><td><hr /></td><td><hr /></td></tr><tr
style="vertical-align:baseline;" id="TBL-3-17-"><td style="text-align:left; white-space:nowrap;" id="TBL-3-17-1"
class="td11"><a
href="../html/man/grdimage.html" ><span
class="phvb8t-x-x-90">grdimage</span></a><a
id="dx1-34011"></a> </td><td style="text-align:left; white-space:nowrap;" id="TBL-3-17-2"
class="td11"><span
class="ptmr8t-x-x-90">Produce color images from 2-D gridded data </span></td>
</tr><tr
class="hline"><td><hr /></td><td><hr /></td></tr><tr
style="vertical-align:baseline;" id="TBL-3-18-"><td style="text-align:left; white-space:nowrap;" id="TBL-3-18-1"
class="td11"><a
href="../html/man/grdvector.html" ><span
class="phvb8t-x-x-90">grdvector</span></a><a
id="dx1-34012"></a> </td><td style="text-align:left; white-space:nowrap;" id="TBL-3-18-2"
class="td11"><span
class="ptmr8t-x-x-90">Plot vector fields from 2-D gridded data </span></td>
</tr><tr
class="hline"><td><hr /></td><td><hr /></td></tr><tr
style="vertical-align:baseline;" id="TBL-3-19-"><td style="text-align:left; white-space:nowrap;" id="TBL-3-19-1"
class="td11"><a
href="../html/man/grdview.html" ><span
class="phvb8t-x-x-90">grdview</span></a><a
id="dx1-34013"></a> </td><td style="text-align:left; white-space:nowrap;" id="TBL-3-19-2"
class="td11"><span
class="ptmr8t-x-x-90">3-D perspective imaging of 2-D gridded data </span></td>
</tr><tr
class="hline"><td><hr /></td><td><hr /></td></tr><tr
style="vertical-align:baseline;" id="TBL-3-20-"><td colspan="2" style="text-align:center; white-space:nowrap;" id="TBL-3-20-1"
class="td11"> <div class="multicolumn" style="text-align:center; white-space:nowrap;"><span
class="ptmri8t-x-x-90">UTILITIES</span></div>
</td></tr><tr
class="hline"><td><hr /></td><td><hr /></td></tr><tr
style="vertical-align:baseline;" id="TBL-3-21-"><td style="text-align:left; white-space:nowrap;" id="TBL-3-21-1"
class="td11"><a
href="../html/man/psclip.html" ><span
class="phvb8t-x-x-90">psclip</span></a><a
id="dx1-34014"></a> </td><td style="text-align:left; white-space:nowrap;" id="TBL-3-21-2"
class="td11"><span
class="ptmr8t-x-x-90">Use polygon files to initiate custom clipping paths </span></td>
</tr><tr
class="hline"><td><hr /></td><td><hr /></td></tr><tr
style="vertical-align:baseline;" id="TBL-3-22-"><td style="text-align:left; white-space:nowrap;" id="TBL-3-22-1"
class="td11"><a
href="../html/man/psimage.html" ><span
class="phvb8t-x-x-90">psimage</span></a><a
id="dx1-34015"></a> </td><td style="text-align:left; white-space:nowrap;" id="TBL-3-22-2"
class="td11"><span
class="ptmr8t-x-x-90">Plot Sun raster files </span></td>
</tr><tr
class="hline"><td><hr /></td><td><hr /></td></tr><tr
style="vertical-align:baseline;" id="TBL-3-23-"><td style="text-align:left; white-space:nowrap;" id="TBL-3-23-1"
class="td11"><a
href="../html/man/psmask.html" ><span
class="phvb8t-x-x-90">psmask</span></a><a
id="dx1-34016"></a> </td><td style="text-align:left; white-space:nowrap;" id="TBL-3-23-2"
class="td11"><span
class="ptmr8t-x-x-90">Create clipping paths or generate overlay to mask </span></td>
</tr><tr
class="hline"><td><hr /></td><td><hr /></td></tr><tr
style="vertical-align:baseline;" id="TBL-3-24-"><td style="text-align:left; white-space:nowrap;" id="TBL-3-24-1"
class="td11"><a
href="../html/man/psscale.html" ><span
class="phvb8t-x-x-90">psscale</span></a><a
id="dx1-34017"></a> </td><td style="text-align:left; white-space:nowrap;" id="TBL-3-24-2"
class="td11"><span
class="ptmr8t-x-x-90">Plot gray scale or color scale bar </span></td>
</tr><tr
class="hline"><td><hr /></td><td><hr /></td></tr><tr
style="vertical-align:baseline;" id="TBL-3-25-"><td style="text-align:left; white-space:nowrap;" id="TBL-3-25-1"
class="td11"><a
href="../html/man/pstext.html" ><span
class="phvb8t-x-x-90">pstext</span></a><a
id="dx1-34018"></a> </td><td style="text-align:left; white-space:nowrap;" id="TBL-3-25-2"
class="td11"><span
class="ptmr8t-x-x-90">Plot text strings on maps </span></td>
</tr><tr
class="hline"><td><hr /></td><td><hr /></td></tr><tr
style="vertical-align:baseline;" id="TBL-3-26-"><td style="text-align:left; white-space:nowrap;" id="TBL-3-26-1"
class="td11"> </td></tr></table>
</div>
<br /><div class="caption"
><span class="id">Table 2.1: </span><span
class="content">List of all 1-D and 2-D plotting programs in <a
href="http://gmt.soest.hawaii.edu" ><span
class="ptmb8t-">GMT</span></a>.</span></div><!--tex4ht:label?: x1-34019r1 -->
</div><hr class="endfloat" />
</div>
<!--l. 666--><p class="indent" > Plotting lines and symbols, <a
href="../html/man/psxy.html" ><span
class="phvb8t-">psxy</span></a><a
id="dx1-34020"></a> is one of the most frequently used programs in <a
href="http://gmt.soest.hawaii.edu" ><span
class="ptmb8t-">GMT</span></a>. In addition to the
common command line switches it has numerous specific options, and expects different file formats depending on
what action has been selected. These circumstances make <a
href="../html/man/psxy.html" ><span
class="phvb8t-">psxy</span></a><a
id="dx1-34021"></a> harder to master than most <a
href="http://gmt.soest.hawaii.edu" ><span
class="ptmb8t-">GMT</span></a> tools. Table <a
href="#x1-34022r2">2.2<!--tex4ht:ref: tbl:psxy --></a>
shows a complete list of the options.
</p>
<div class="table">
<!--l. 673--><p class="indent" > <a
id="x1-34022r2"></a></p><hr class="float" /><div class="float"
>
<div class="tabular"> <table id="TBL-4" class="tabular"
cellspacing="0" cellpadding="0" rules="groups"
><colgroup id="TBL-4-1g"><col
id="TBL-4-1" /></colgroup><colgroup id="TBL-4-2g"><col
id="TBL-4-2" /></colgroup><tr
class="hline"><td><hr /></td><td><hr /></td></tr><tr
style="vertical-align:baseline;" id="TBL-4-1-"><td style="text-align:center; white-space:nowrap;" id="TBL-4-1-1"
class="td11"> <div class="multicolumn" style="text-align:center; white-space:nowrap;"><span
class="ptmri8t-x-x-90">Option</span></div> </td><td style="text-align:center; white-space:nowrap;" id="TBL-4-1-2"
class="td11"> <div class="multicolumn" style="text-align:center; white-space:nowrap;"><span
class="ptmri8t-x-x-90">Purpose</span></div>
</td></tr><tr
class="hline"><td><hr /></td><td><hr /></td></tr><tr
style="vertical-align:baseline;" id="TBL-4-2-"><td style="text-align:left; white-space:nowrap;" id="TBL-4-2-1"
class="td11"><span
class="pcrb8t-x-x-90">-A </span></td><td style="text-align:left; white-space:nowrap;" id="TBL-4-2-2"
class="td11"><span
class="ptmr8t-x-x-90">Suppress line interpolation along great circles </span></td>
</tr><tr
class="hline"><td><hr /></td><td><hr /></td></tr><tr
style="vertical-align:baseline;" id="TBL-4-3-"><td style="text-align:left; white-space:nowrap;" id="TBL-4-3-1"
class="td11"><span
class="pcrb8t-x-x-90">-C</span><span
class="ptmri8t-x-x-90">cpt </span></td><td style="text-align:left; white-space:nowrap;" id="TBL-4-3-2"
class="td11"><span
class="ptmr8t-x-x-90">Let symbol color be determined from </span><!--l. 679--><math
xmlns="http://www.w3.org/1998/Math/MathML"
display="inline" ><mi
>z</mi></math><span
class="ptmr8t-x-x-90">-values and the </span><span
class="ptmri8t-x-x-90">cpt </span><span
class="ptmr8t-x-x-90">file</span></td>
</tr><tr
class="hline"><td><hr /></td><td><hr /></td></tr><tr
style="vertical-align:baseline;" id="TBL-4-4-"><td style="text-align:left; white-space:nowrap;" id="TBL-4-4-1"
class="td11"><span
class="pcrb8t-x-x-90">-E</span><span
class="ptmr8t-x-x-90">[</span><span
class="ptmb8t-x-x-90">x</span><!--l. 680--><math
xmlns="http://www.w3.org/1998/Math/MathML"
display="inline" ><mo
class="MathClass-rel">|</mo></math><span
class="ptmb8t-x-x-90">X</span><span
class="ptmr8t-x-x-90">][</span><span
class="ptmb8t-x-x-90">y</span><!--l. 680--><math
xmlns="http://www.w3.org/1998/Math/MathML"
display="inline" ><mo
class="MathClass-rel">|</mo></math><span
class="ptmb8t-x-x-90">Y</span><span
class="ptmr8t-x-x-90">][</span><span
class="ptmri8t-x-x-90">cap</span><span
class="ptmr8t-x-x-90">][/</span><span
class="ptmri8t-x-x-90">pen</span><span
class="ptmr8t-x-x-90">]</span></td><td style="text-align:left; white-space:nowrap;" id="TBL-4-4-2"
class="td11"><span
class="ptmr8t-x-x-90">Draw selected error bars with specified attributes </span></td>
</tr><tr
class="hline"><td><hr /></td><td><hr /></td></tr><tr
style="vertical-align:baseline;" id="TBL-4-5-"><td style="text-align:left; white-space:nowrap;" id="TBL-4-5-1"
class="td11"><span
class="pcrb8t-x-x-90">-G</span><span
class="ptmri8t-x-x-90">fill </span></td><td style="text-align:left; white-space:nowrap;" id="TBL-4-5-2"
class="td11"><span
class="ptmr8t-x-x-90">Set color for symbol or fill for polygons </span></td>
</tr><tr
class="hline"><td><hr /></td><td><hr /></td></tr><tr
style="vertical-align:baseline;" id="TBL-4-6-"><td style="text-align:left; white-space:nowrap;" id="TBL-4-6-1"
class="td11"><span
class="pcrb8t-x-x-90">-L </span></td><td style="text-align:left; white-space:nowrap;" id="TBL-4-6-2"
class="td11"><span
class="ptmr8t-x-x-90">Explicitly close polygons </span></td>
</tr><tr
class="hline"><td><hr /></td><td><hr /></td></tr><tr
style="vertical-align:baseline;" id="TBL-4-7-"><td style="text-align:left; white-space:nowrap;" id="TBL-4-7-1"
class="td11"><span
class="pcrb8t-x-x-90">-N </span></td><td style="text-align:left; white-space:nowrap;" id="TBL-4-7-2"
class="td11"><span
class="ptmr8t-x-x-90">Do Not clip symbols at map borders </span></td>
</tr><tr
class="hline"><td><hr /></td><td><hr /></td></tr><tr
style="vertical-align:baseline;" id="TBL-4-8-"><td style="text-align:left; white-space:nowrap;" id="TBL-4-8-1"
class="td11"><span
class="pcrb8t-x-x-90">-S[symbol]</span><span
class="ptmr8t-x-x-90">[</span><span
class="ptmri8t-x-x-90">size</span><span
class="ptmr8t-x-x-90">] </span></td><td style="text-align:left; white-space:nowrap;" id="TBL-4-8-2"
class="td11"><span
class="ptmr8t-x-x-90">Select one of several symbols (See Table</span><span
class="ptmr8t-x-x-90"> </span><a
href="#x1-34026r3"><span
class="ptmr8t-x-x-90">2.3</span><!--tex4ht:ref: tbl:psxysymbols --></a><span
class="ptmr8t-x-x-90">) </span></td>
</tr><tr
class="hline"><td><hr /></td><td><hr /></td></tr><tr
style="vertical-align:baseline;" id="TBL-4-9-"><td style="text-align:left; white-space:nowrap;" id="TBL-4-9-1"
class="td11"><span
class="pcrb8t-x-x-90">-W</span><span
class="ptmri8t-x-x-90">pen </span></td><td style="text-align:left; white-space:nowrap;" id="TBL-4-9-2"
class="td11"><span
class="ptmr8t-x-x-90">Set </span><span
class="ptmri8t-x-x-90">pen </span><span
class="ptmr8t-x-x-90">for line or symbol outline </span></td>
</tr><tr
class="hline"><td><hr /></td><td><hr /></td></tr><tr
style="vertical-align:baseline;" id="TBL-4-10-"><td style="text-align:left; white-space:nowrap;" id="TBL-4-10-1"
class="td11"><span
class="pcrb8t-x-x-90">-m</span><span
class="ptmr8t-x-x-90">[</span><span
class="ptmri8t-x-x-90">flag</span><span
class="ptmr8t-x-x-90">] </span></td><td style="text-align:left; white-space:nowrap;" id="TBL-4-10-2"
class="td11"><span
class="ptmr8t-x-x-90">Multiple segment input data; headers start with </span><span
class="ptmri8t-x-x-90">flag </span></td>
</tr><tr
class="hline"><td><hr /></td><td><hr /></td></tr><tr
style="vertical-align:baseline;" id="TBL-4-11-"><td style="text-align:left; white-space:nowrap;" id="TBL-4-11-1"
class="td11"> </td></tr></table>
</div>
<br /><div class="caption"
><span class="id">Table 2.2: </span><span
class="content">Optional switches in the <a
href="../html/man/psxy.html" ><span
class="phvb8t-">psxy</span></a><a
id="dx1-34023"></a> program.</span></div><!--tex4ht:label?: x1-34022r2 -->
</div><hr class="endfloat" />
</div>
<!--l. 692--><p class="indent" > The symbols can either be transparent (using <span
class="pcrb8t-">-W </span>only, not <span
class="pcrb8t-">-G</span>) or solid (<span
class="pcrb8t-">-G</span>, with optional outline using <span
class="pcrb8t-">-W</span>).
The <span
class="pcrb8t-">-S </span>option takes the code for the desired symbol and optional size information. If no symbol is given it is
expected to be given in the last column of each record in the input file. The <span
class="ptmri8t-">size </span>is optional since individual sizes
for symbols may also be provided by the input data. The main symbols available to us are shown in
Table <a
href="#x1-34026r3">2.3<!--tex4ht:ref: tbl:psxysymbols --></a>.
</p>
<div class="table">
<!--l. 700--><p class="indent" > <a
id="x1-34026r3"></a></p><hr class="float" /><div class="float"
>
<a
id="dx1-34024"></a>
<a
id="dx1-34025"></a>
<div class="tabular"> <table id="TBL-5" class="tabular"
cellspacing="0" cellpadding="0" rules="groups"
><colgroup id="TBL-5-1g"><col
id="TBL-5-1" /></colgroup><colgroup id="TBL-5-2g"><col
id="TBL-5-2" /></colgroup><tr
class="hline"><td><hr /></td><td><hr /></td></tr><tr
style="vertical-align:baseline;" id="TBL-5-1-"><td style="text-align:center; white-space:nowrap;" id="TBL-5-1-1"
class="td11"> <div class="multicolumn" style="text-align:center; white-space:nowrap;"><span
class="ptmri8t-x-x-90">Option</span></div> </td><td style="text-align:center; white-space:nowrap;" id="TBL-5-1-2"
class="td11"> <div class="multicolumn" style="text-align:center; white-space:nowrap;"><span
class="ptmri8t-x-x-90">Symbol</span></div>
</td></tr><tr
class="hline"><td><hr /></td><td><hr /></td></tr><tr
style="vertical-align:baseline;" id="TBL-5-2-"><td style="text-align:left; white-space:nowrap;" id="TBL-5-2-1"
class="td11"><span
class="pcrb8t-x-x-90">-S-</span><span
class="ptmri8t-x-x-90">size </span></td><td style="text-align:left; white-space:nowrap;" id="TBL-5-2-2"
class="td11"><span
class="ptmr8t-x-x-90">horizontal dash; </span><span
class="ptmri8t-x-x-90">size </span><span
class="ptmr8t-x-x-90">is length of dash </span></td>
</tr><tr
class="hline"><td><hr /></td><td><hr /></td></tr><tr
style="vertical-align:baseline;" id="TBL-5-3-"><td style="text-align:left; white-space:nowrap;" id="TBL-5-3-1"
class="td11"><span
class="pcrb8t-x-x-90">-Sa</span><span
class="ptmri8t-x-x-90">size </span></td><td style="text-align:left; white-space:nowrap;" id="TBL-5-3-2"
class="td11"><span
class="ptmr8t-x-x-90">st</span><span
class="ptmb8t-x-x-90">a</span><span
class="ptmr8t-x-x-90">r; </span><span
class="ptmri8t-x-x-90">size </span><span
class="ptmr8t-x-x-90">is radius of circumscribing circle </span></td>
</tr><tr
class="hline"><td><hr /></td><td><hr /></td></tr><tr
style="vertical-align:baseline;" id="TBL-5-4-"><td style="text-align:left; white-space:nowrap;" id="TBL-5-4-1"
class="td11"><span
class="pcrb8t-x-x-90">-Sb</span><span
class="ptmri8t-x-x-90">size</span><span
class="ptmr8t-x-x-90">[/</span><span
class="ptmri8t-x-x-90">base</span><span
class="ptmr8t-x-x-90">][</span><span
class="ptmb8t-x-x-90">u</span><span
class="ptmr8t-x-x-90">] </span></td><td style="text-align:left; white-space:nowrap;" id="TBL-5-4-2"
class="td11"><span
class="ptmb8t-x-x-90">b</span><span
class="ptmr8t-x-x-90">ar; </span><span
class="ptmri8t-x-x-90">size </span><span
class="ptmr8t-x-x-90">is bar width, append </span><span
class="ptmb8t-x-x-90">u </span><span
class="ptmr8t-x-x-90">if </span><span
class="ptmri8t-x-x-90">size </span><span
class="ptmr8t-x-x-90">is in </span><span
class="ptmri8t-x-x-90">x</span><span
class="ptmr8t-x-x-90">-units </span></td>
</tr><tr
style="vertical-align:baseline;" id="TBL-5-5-"><td style="text-align:left; white-space:nowrap;" id="TBL-5-5-1"
class="td11"> </td><td style="text-align:left; white-space:nowrap;" id="TBL-5-5-2"
class="td11"><span
class="ptmr8t-x-x-90">Bar extends from </span><span
class="ptmri8t-x-x-90">base </span><span
class="ptmr8t-x-x-90">[0] to the </span><span
class="ptmri8t-x-x-90">y</span><span
class="ptmr8t-x-x-90">-value </span></td>
</tr><tr
class="hline"><td><hr /></td><td><hr /></td></tr><tr
style="vertical-align:baseline;" id="TBL-5-6-"><td style="text-align:left; white-space:nowrap;" id="TBL-5-6-1"
class="td11"><span
class="pcrb8t-x-x-90">-Sc</span><span
class="ptmri8t-x-x-90">size </span></td><td style="text-align:left; white-space:nowrap;" id="TBL-5-6-2"
class="td11"><span
class="ptmb8t-x-x-90">c</span><span
class="ptmr8t-x-x-90">ircle; </span><span
class="ptmri8t-x-x-90">size </span><span
class="ptmr8t-x-x-90">is the diameter </span></td>
</tr><tr
class="hline"><td><hr /></td><td><hr /></td></tr><tr
style="vertical-align:baseline;" id="TBL-5-7-"><td style="text-align:left; white-space:nowrap;" id="TBL-5-7-1"
class="td11"><span
class="pcrb8t-x-x-90">-Sd</span><span
class="ptmri8t-x-x-90">size </span></td><td style="text-align:left; white-space:nowrap;" id="TBL-5-7-2"
class="td11"><span
class="ptmb8t-x-x-90">d</span><span
class="ptmr8t-x-x-90">iamond; </span><span
class="ptmri8t-x-x-90">size </span><span
class="ptmr8t-x-x-90">is its side </span></td>
</tr><tr
class="hline"><td><hr /></td><td><hr /></td></tr><tr
style="vertical-align:baseline;" id="TBL-5-8-"><td style="text-align:left; white-space:nowrap;" id="TBL-5-8-1"
class="td11"><span
class="pcrb8t-x-x-90">-Se </span></td><td style="text-align:left; white-space:nowrap;" id="TBL-5-8-2"
class="td11"><span
class="ptmb8t-x-x-90">e</span><span
class="ptmr8t-x-x-90">llipse; </span><span
class="ptmri8t-x-x-90">direction </span><span
class="ptmr8t-x-x-90">(CCW from horizontal), </span><span
class="ptmri8t-x-x-90">major</span><span
class="ptmr8t-x-x-90">, and </span><span
class="ptmri8t-x-x-90">minor </span><span
class="ptmr8t-x-x-90">axes in inches </span></td>
</tr><tr
style="vertical-align:baseline;" id="TBL-5-9-"><td style="text-align:left; white-space:nowrap;" id="TBL-5-9-1"
class="td11"> </td><td style="text-align:left; white-space:nowrap;" id="TBL-5-9-2"
class="td11"><span
class="ptmr8t-x-x-90">are read from the input file </span></td>
</tr><tr
class="hline"><td><hr /></td><td><hr /></td></tr><tr
style="vertical-align:baseline;" id="TBL-5-10-"><td style="text-align:left; white-space:nowrap;" id="TBL-5-10-1"
class="td11"><span
class="pcrb8t-x-x-90">-SE </span></td><td style="text-align:left; white-space:nowrap;" id="TBL-5-10-2"
class="td11"><span
class="ptmb8t-x-x-90">e</span><span
class="ptmr8t-x-x-90">llipse; </span><span
class="ptmri8t-x-x-90">azimuth </span><span
class="ptmr8t-x-x-90">(CW from vertical), </span><span
class="ptmri8t-x-x-90">major</span><span
class="ptmr8t-x-x-90">, and </span><span
class="ptmri8t-x-x-90">minor </span><span
class="ptmr8t-x-x-90">axes in kilometers </span></td>
</tr><tr
style="vertical-align:baseline;" id="TBL-5-11-"><td style="text-align:left; white-space:nowrap;" id="TBL-5-11-1"
class="td11"> </td><td style="text-align:left; white-space:nowrap;" id="TBL-5-11-2"
class="td11"><span
class="ptmr8t-x-x-90">are read from the input file </span></td>
</tr><tr
class="hline"><td><hr /></td><td><hr /></td></tr><tr
style="vertical-align:baseline;" id="TBL-5-12-"><td style="text-align:left; white-space:nowrap;" id="TBL-5-12-1"
class="td11"><span
class="pcrb8t-x-x-90">-Sg</span><span
class="ptmri8t-x-x-90">size </span></td><td style="text-align:left; white-space:nowrap;" id="TBL-5-12-2"
class="td11"><span
class="ptmr8t-x-x-90">octa</span><span
class="ptmb8t-x-x-90">g</span><span
class="ptmr8t-x-x-90">on; </span><span
class="ptmri8t-x-x-90">size </span><span
class="ptmr8t-x-x-90">is its side </span></td>
</tr><tr
class="hline"><td><hr /></td><td><hr /></td></tr><tr
style="vertical-align:baseline;" id="TBL-5-13-"><td style="text-align:left; white-space:nowrap;" id="TBL-5-13-1"
class="td11"><span
class="pcrb8t-x-x-90">-Sh</span><span
class="ptmri8t-x-x-90">size </span></td><td style="text-align:left; white-space:nowrap;" id="TBL-5-13-2"
class="td11"><span
class="ptmb8t-x-x-90">h</span><span
class="ptmr8t-x-x-90">exagon; </span><span
class="ptmri8t-x-x-90">size </span><span
class="ptmr8t-x-x-90">is its side </span></td>
</tr><tr
class="hline"><td><hr /></td><td><hr /></td></tr><tr
style="vertical-align:baseline;" id="TBL-5-14-"><td style="text-align:left; white-space:nowrap;" id="TBL-5-14-1"
class="td11"><span
class="pcrb8t-x-x-90">-Si</span><span
class="ptmri8t-x-x-90">size </span></td><td style="text-align:left; white-space:nowrap;" id="TBL-5-14-2"
class="td11"><span
class="ptmb8t-x-x-90">i</span><span
class="ptmr8t-x-x-90">nverted triangle; </span><span
class="ptmri8t-x-x-90">size </span><span
class="ptmr8t-x-x-90">is its side </span></td>
</tr><tr
class="hline"><td><hr /></td><td><hr /></td></tr><tr
style="vertical-align:baseline;" id="TBL-5-15-"><td style="text-align:left; white-space:nowrap;" id="TBL-5-15-1"
class="td11"><span
class="pcrb8t-x-x-90">-Sk</span><span
class="ptmri8t-x-x-90">symbol</span><span
class="ptmr8t-x-x-90">/</span><span
class="ptmri8t-x-x-90">size </span></td><td style="text-align:left; white-space:nowrap;" id="TBL-5-15-2"
class="td11"><span
class="ptmb8t-x-x-90">k</span><span
class="ptmr8t-x-x-90">ustom symbol; </span><span
class="ptmri8t-x-x-90">size </span><span
class="ptmr8t-x-x-90">is its side </span></td>
</tr><tr
class="hline"><td><hr /></td><td><hr /></td></tr><tr
style="vertical-align:baseline;" id="TBL-5-16-"><td style="text-align:left; white-space:nowrap;" id="TBL-5-16-1"
class="td11"><span
class="pcrb8t-x-x-90">-Sl</span><span
class="ptmri8t-x-x-90">size</span><span
class="ptmr8t-x-x-90">/</span><span
class="ptmri8t-x-x-90">string</span><span
class="ptmr8t-x-x-90">[%</span><span
class="ptmri8t-x-x-90">font</span><span
class="ptmr8t-x-x-90">] </span></td><td style="text-align:left; white-space:nowrap;" id="TBL-5-16-2"
class="td11"><span
class="ptmb8t-x-x-90">l</span><span
class="ptmr8t-x-x-90">etter; </span><span
class="ptmri8t-x-x-90">size </span><span
class="ptmr8t-x-x-90">is fontsize. Append a letter or text string, and optionally a font </span></td>
</tr><tr
class="hline"><td><hr /></td><td><hr /></td></tr><tr
style="vertical-align:baseline;" id="TBL-5-17-"><td style="text-align:left; white-space:nowrap;" id="TBL-5-17-1"
class="td11"><span
class="pcrb8t-x-x-90">-Sn</span><span
class="ptmri8t-x-x-90">size </span></td><td style="text-align:left; white-space:nowrap;" id="TBL-5-17-2"
class="td11"><span
class="ptmr8t-x-x-90">pe</span><span
class="ptmb8t-x-x-90">n</span><span
class="ptmr8t-x-x-90">tagon; </span><span
class="ptmri8t-x-x-90">size </span><span
class="ptmr8t-x-x-90">is its side </span></td>
</tr><tr
class="hline"><td><hr /></td><td><hr /></td></tr><tr
style="vertical-align:baseline;" id="TBL-5-18-"><td style="text-align:left; white-space:nowrap;" id="TBL-5-18-1"
class="td11"><span
class="pcrb8t-x-x-90">-Sp </span></td><td style="text-align:left; white-space:nowrap;" id="TBL-5-18-2"
class="td11"><span
class="ptmb8t-x-x-90">p</span><span
class="ptmr8t-x-x-90">oint; no size needed (1 pixel at current resolution is used) </span></td>
</tr><tr
class="hline"><td><hr /></td><td><hr /></td></tr><tr
style="vertical-align:baseline;" id="TBL-5-19-"><td style="text-align:left; white-space:nowrap;" id="TBL-5-19-1"
class="td11"><span
class="pcrb8t-x-x-90">-Sr</span><span
class="ptmri8t-x-x-90">size </span></td><td style="text-align:left; white-space:nowrap;" id="TBL-5-19-2"
class="td11"><span
class="ptmb8t-x-x-90">r</span><span
class="ptmr8t-x-x-90">ect, </span><span
class="ptmri8t-x-x-90">width </span><span
class="ptmr8t-x-x-90">and </span><span
class="ptmri8t-x-x-90">height </span><span
class="ptmr8t-x-x-90">are read from input file </span></td>
</tr><tr
class="hline"><td><hr /></td><td><hr /></td></tr><tr
style="vertical-align:baseline;" id="TBL-5-20-"><td style="text-align:left; white-space:nowrap;" id="TBL-5-20-1"
class="td11"><span
class="pcrb8t-x-x-90">-Ss</span><span
class="ptmri8t-x-x-90">size </span></td><td style="text-align:left; white-space:nowrap;" id="TBL-5-20-2"
class="td11"><span
class="ptmb8t-x-x-90">s</span><span
class="ptmr8t-x-x-90">quare, </span><span
class="ptmri8t-x-x-90">size </span><span
class="ptmr8t-x-x-90">is its side </span></td>
</tr><tr
class="hline"><td><hr /></td><td><hr /></td></tr><tr
style="vertical-align:baseline;" id="TBL-5-21-"><td style="text-align:left; white-space:nowrap;" id="TBL-5-21-1"
class="td11"><span
class="pcrb8t-x-x-90">-St</span><span
class="ptmri8t-x-x-90">size </span></td><td style="text-align:left; white-space:nowrap;" id="TBL-5-21-2"
class="td11"><span
class="ptmb8t-x-x-90">t</span><span
class="ptmr8t-x-x-90">riangle; </span><span
class="ptmri8t-x-x-90">size </span><span
class="ptmr8t-x-x-90">is its side </span></td>
</tr><tr
class="hline"><td><hr /></td><td><hr /></td></tr><tr
style="vertical-align:baseline;" id="TBL-5-22-"><td style="text-align:left; white-space:nowrap;" id="TBL-5-22-1"
class="td11"><span
class="pcrb8t-x-x-90">-Sv</span><span
class="ptmr8t-x-x-90">[</span><span
class="ptmri8t-x-x-90">thick</span><span
class="ptmr8t-x-x-90">/</span><span
class="ptmri8t-x-x-90">length</span><span
class="ptmr8t-x-x-90">/</span><span
class="ptmri8t-x-x-90">width</span><span
class="ptmr8t-x-x-90">][</span><span
class="ptmb8t-x-x-90">n</span><span
class="ptmri8t-x-x-90">norm</span><span
class="ptmr8t-x-x-90">]</span></td><td style="text-align:left; white-space:nowrap;" id="TBL-5-22-2"
class="td11"><span
class="ptmb8t-x-x-90">v</span><span
class="ptmr8t-x-x-90">ector; </span><span
class="ptmri8t-x-x-90">direction </span><span
class="ptmr8t-x-x-90">(CCW from horizontal) and </span><span
class="ptmri8t-x-x-90">length </span><span
class="ptmr8t-x-x-90">are read from input data </span></td>
</tr><tr
style="vertical-align:baseline;" id="TBL-5-23-"><td style="text-align:left; white-space:nowrap;" id="TBL-5-23-1"
class="td11"> </td><td style="text-align:left; white-space:nowrap;" id="TBL-5-23-2"
class="td11"><span
class="ptmr8t-x-x-90">Optionally, append the thickness of the vector and the width and length of the</span></td>
</tr><tr
style="vertical-align:baseline;" id="TBL-5-24-"><td style="text-align:left; white-space:nowrap;" id="TBL-5-24-1"
class="td11"> </td><td style="text-align:left; white-space:nowrap;" id="TBL-5-24-2"
class="td11"><span
class="ptmr8t-x-x-90">arrow-head. If the </span><span
class="ptmb8t-x-x-90">n</span><span
class="ptmri8t-x-x-90">norm </span><span
class="ptmr8t-x-x-90">is appended, all vectors whose lengths are less than </span></td>
</tr><tr
style="vertical-align:baseline;" id="TBL-5-25-"><td style="text-align:left; white-space:nowrap;" id="TBL-5-25-1"
class="td11"> </td><td style="text-align:left; white-space:nowrap;" id="TBL-5-25-2"
class="td11"><span
class="ptmri8t-x-x-90">norm </span><span
class="ptmr8t-x-x-90">will have their attributes scaled by length/</span><span
class="ptmri8t-x-x-90">norm </span></td>
</tr><tr
class="hline"><td><hr /></td><td><hr /></td></tr><tr
style="vertical-align:baseline;" id="TBL-5-26-"><td style="text-align:left; white-space:nowrap;" id="TBL-5-26-1"
class="td11"><span
class="pcrb8t-x-x-90">-SV</span><span
class="ptmr8t-x-x-90">[</span><span
class="ptmri8t-x-x-90">thick</span><span
class="ptmr8t-x-x-90">/</span><span
class="ptmri8t-x-x-90">length</span><span
class="ptmr8t-x-x-90">/</span><span
class="ptmri8t-x-x-90">width</span><span
class="ptmr8t-x-x-90">][</span><span
class="ptmb8t-x-x-90">n</span><span
class="ptmri8t-x-x-90">norm</span><span
class="ptmr8t-x-x-90">]</span></td><td style="text-align:left; white-space:nowrap;" id="TBL-5-26-2"
class="td11"><span
class="ptmb8t-x-x-90">v</span><span
class="ptmr8t-x-x-90">ector, except </span><span
class="ptmri8t-x-x-90">azimuth </span><span
class="ptmr8t-x-x-90">(degrees east of north) is expected instead of </span><span
class="ptmri8t-x-x-90">direction </span></td>
</tr><tr
style="vertical-align:baseline;" id="TBL-5-27-"><td style="text-align:left; white-space:nowrap;" id="TBL-5-27-1"
class="td11"> </td><td style="text-align:left; white-space:nowrap;" id="TBL-5-27-2"
class="td11"><span
class="ptmr8t-x-x-90">The angle on the map is calculated based on the chosen map projection </span></td>
</tr><tr
class="hline"><td><hr /></td><td><hr /></td></tr><tr
style="vertical-align:baseline;" id="TBL-5-28-"><td style="text-align:left; white-space:nowrap;" id="TBL-5-28-1"
class="td11"><span
class="pcrb8t-x-x-90">-Sw</span><span
class="ptmr8t-x-x-90">[</span><span
class="ptmri8t-x-x-90">size </span></td><td style="text-align:left; white-space:nowrap;" id="TBL-5-28-2"
class="td11"><span
class="ptmr8t-x-x-90">pie </span><span
class="ptmb8t-x-x-90">w</span><span
class="ptmr8t-x-x-90">edge; </span><span
class="ptmri8t-x-x-90">start </span><span
class="ptmr8t-x-x-90">and </span><span
class="ptmri8t-x-x-90">stop </span><span
class="ptmr8t-x-x-90">directions (CCW from horizontal) are read from </span></td>
</tr><tr
style="vertical-align:baseline;" id="TBL-5-29-"><td style="text-align:left; white-space:nowrap;" id="TBL-5-29-1"
class="td11"> </td><td style="text-align:left; white-space:nowrap;" id="TBL-5-29-2"
class="td11"><span
class="ptmr8t-x-x-90">input data </span></td>
</tr><tr
class="hline"><td><hr /></td><td><hr /></td></tr><tr
style="vertical-align:baseline;" id="TBL-5-30-"><td style="text-align:left; white-space:nowrap;" id="TBL-5-30-1"
class="td11"><span
class="pcrb8t-x-x-90">-Sx</span><span
class="ptmri8t-x-x-90">size </span></td><td style="text-align:left; white-space:nowrap;" id="TBL-5-30-2"
class="td11"><span
class="ptmr8t-x-x-90">cross; </span><span
class="ptmri8t-x-x-90">size </span><span
class="ptmr8t-x-x-90">is length of crossing lines </span></td>
</tr><tr
class="hline"><td><hr /></td><td><hr /></td></tr><tr
style="vertical-align:baseline;" id="TBL-5-31-"><td style="text-align:left; white-space:nowrap;" id="TBL-5-31-1"
class="td11"><span
class="pcrb8t-x-x-90">-Sy</span><span
class="ptmri8t-x-x-90">size </span></td><td style="text-align:left; white-space:nowrap;" id="TBL-5-31-2"
class="td11"><span
class="ptmr8t-x-x-90">vertical dash; </span><span
class="ptmri8t-x-x-90">size </span><span
class="ptmr8t-x-x-90">is length of dash </span></td>
</tr><tr
class="hline"><td><hr /></td><td><hr /></td></tr><tr
style="vertical-align:baseline;" id="TBL-5-32-"><td style="text-align:left; white-space:nowrap;" id="TBL-5-32-1"
class="td11"> </td></tr></table></div>
<br /> <div class="caption"
><span class="id">Table 2.3: </span><span
class="content">The symbol option in <a
href="../html/man/psxy.html" ><span
class="phvb8t-">psxy</span></a><a
id="dx1-34027"></a>. Lower case symbols (<span
class="ptmb8t-">a, c, d, g, h, i, n, s, t, x</span>) will fit inside a
circle of given diameter. Upper case symbols (<span
class="ptmb8t-">A, C, D, G, H, I, N, S, T, X</span>) will have area equal to that of
a circle of given diameter.</span></div><!--tex4ht:label?: x1-34026r3 -->
</div><hr class="endfloat" />
</div>
<!--l. 743--><p class="indent" > Because some symbols require more input data than others, and because the size of symbols as well as their
color can be determined from the input data, the format of data can be confusing. The general format for the input
data is (optional items are in brackets []): <br
class="newline" /><a
id="dx1-34028"></a>
</p><!--l. 749--><p class="indent" > <!--l. 749--><math
xmlns="http://www.w3.org/1998/Math/MathML"
display="inline" ><mi
>x</mi><mstyle
class="mbox"><mtext > </mtext></mstyle><mi
>y</mi></math> [
<!--l. 749--><math
xmlns="http://www.w3.org/1998/Math/MathML"
display="inline" ><mi
>z</mi></math> ] [
<!--l. 749--><math
xmlns="http://www.w3.org/1998/Math/MathML"
display="inline" ><mi
>s</mi><mi
>i</mi><mi
>z</mi><mi
>e</mi></math> ] [
<!--l. 749--><math
xmlns="http://www.w3.org/1998/Math/MathML"
display="inline" ><msub><mrow
><mi
>σ</mi></mrow><mrow
><mi
>x</mi></mrow></msub
></math> ] [
<!--l. 749--><math
xmlns="http://www.w3.org/1998/Math/MathML"
display="inline" ><msub><mrow
><mi
>σ</mi></mrow><mrow
><mi
>y</mi></mrow></msub
></math> ] [
<!--l. 749--><math
xmlns="http://www.w3.org/1998/Math/MathML"
display="inline" ><mi
>s</mi><mi
>y</mi><mi
>m</mi><mi
>b</mi><mi
>o</mi><mi
>l</mi></math> ]
<br
class="newline" />
</p><!--l. 751--><p class="indent" > Thus, the only required input columns are the first two which must contain the longitude and
latitude (or <span
class="ptmri8t-">x </span>and <span
class="ptmri8t-">y</span>). The remaining items apply when one (or more) of the following conditions are
met:
</p><ol class="enumerate1" >
<li
class="enumerate" id="x1-34030x1">If you want the color of each symbol to be determined individually, supply a cptfile with the <span
class="pcrb8t-">-C </span>option
and let the 3rd data column contain the <span
class="ptmri8t-">z</span>-values to be used with the cptfile.
</li>
<li
class="enumerate" id="x1-34032x2">If you want the size of each symbol to be determined individually, append the size in a separate column.
</li>
<li
class="enumerate" id="x1-34034x3">To draw error bars, use the <span
class="pcrb8t-">-E </span>option and give one or two additional data columns with the <span
class="ptmr8c-">±</span>dx and
<span
class="ptmr8c-">±</span>dy values; the form of <span
class="pcrb8t-">-E </span>determines if one (<span
class="pcrb8t-">-Ex </span>or <span
class="pcrb8t-">-Ey</span>) or two (<span
class="pcrb8t-">-Exy</span>) columns are needed. If
upper case flags <span
class="ptmb8t-">X </span>or <span
class="ptmb8t-">Y </span>are given then we will instead draw a “box-and-whisker” symbol and the
<!--l. 768--><math
xmlns="http://www.w3.org/1998/Math/MathML"
display="inline" ><msub><mrow
><mi
>σ</mi></mrow><mrow
><mi
>x</mi></mrow></msub
></math>
(or <!--l. 769--><math
xmlns="http://www.w3.org/1998/Math/MathML"
display="inline" ><msub><mrow
><mi
>σ</mi></mrow><mrow
><mi
>y</mi></mrow></msub
></math>)
must represent 4 columns containing the minimum, the 25 and 75% quartiles, and the maximum value.
The given <!--l. 770--><math
xmlns="http://www.w3.org/1998/Math/MathML"
display="inline" ><mi
>x</mi></math>
(or <!--l. 770--><math
xmlns="http://www.w3.org/1998/Math/MathML"
display="inline" ><mi
>y</mi></math>)
coordinate is taken as the 50% quartile (median). <a
id="dx1-34035"></a>
</li>
<li
class="enumerate" id="x1-34037x4">If you draw vectors with <span
class="pcrb8t-">-Sv </span>(or <span
class="pcrb8t-">-SV</span>) then <span
class="ptmri8t-">size </span>is actually two columns containing the <span
class="ptmri8t-">direction </span>(or
<span
class="ptmri8t-">azimuth</span>) and <span
class="ptmri8t-">length </span>of each vector. <a
id="dx1-34038"></a>
</li>
<li
class="enumerate" id="x1-34040x5">If you draw ellipses (<span
class="pcrb8t-">-Se</span>) then <span
class="ptmri8t-">size </span>is actually three columns containing the <span
class="ptmri8t-">direction </span>and the <span
class="ptmri8t-">major</span>
and <span
class="ptmri8t-">minor </span>axes in plot units (with <span
class="pcrb8t-">-SE </span>we expect <span
class="ptmri8t-">azimuth </span>instead and axes lengths in km). <a
id="dx1-34041"></a>
</li></ol>
<!--l. 787--><p class="indent" > Before we try some examples we need to review two key switches; they specify pen attributes and symbol or
polygon fill. Please consult Chapter 4 in the <a
href="http://gmt.soest.hawaii.edu" ><span
class="ptmb8t-">GMT</span></a> Technical Reference and Cookbook before experimenting with
the examples below.
</p>
<h4 class="subsectionHead"><span class="titlemark">2.1.1 </span> <a
id="x1-350002.1.1"></a>Examples</h4>
<a
id="dx1-35001"></a>
<!--l. 795--><p class="noindent" >We will start off using the file <span class="underline">data</span> in your directory. Using the <a
href="http://gmt.soest.hawaii.edu" ><span
class="ptmb8t-">GMT</span></a> utility <a
href="../html/man/minmax.html" ><span
class="phvb8t-">minmax</span></a><a
id="dx1-35002"></a> we find the extent of the
data region:
</p>
<div class="verbatim" id="verbatim-11">
minmax data
</div>
<!--l. 801--><p class="nopar" >
</p><!--l. 804--><p class="noindent" >which returns
</p>
<div class="verbatim" id="verbatim-12">
data: N = 7   <1/5>   <1/5>
</div>
<!--l. 809--><p class="nopar" >
</p><!--l. 812--><p class="noindent" >telling us that the file <span class="underline">data</span> has 7 records and gives the minimum and maximum values for the first
two columns. Given our knowledge of how to set up linear projections with <span
class="pcrb8t-">-R </span>and <span
class="pcrb8t-">-JX</span>, try the
following:
</p><!--l. 818--><p class="indent" >
</p><ol class="enumerate1" >
<li
class="enumerate" id="x1-35004x1">Plot the data as transparent circles of size 0.3 inches.
</li>
<li
class="enumerate" id="x1-35006x2">Plot the data as solid white circles instead.
</li>
<li
class="enumerate" id="x1-35008x3">Plot the data using 0.5" stars, making them red with a thick (width = 1.5p), dashed pen.
</li></ol>
<!--l. 829--><p class="indent" > To simply plot the data as a line we choose no symbol and specify a pen thickness instead:
</p>
<div class="verbatim" id="verbatim-13">
psxy data -R -J -P -B -Wthinner > plot.ps
</div>
<!--l. 833--><p class="nopar" ><a
id="dx1-35009"></a>
</p><!--l. 837--><p class="noindent" >
</p>
<h4 class="subsectionHead"><span class="titlemark">2.1.2 </span> <a
id="x1-360002.1.2"></a>Exercises</h4>
<a
id="dx1-36001"></a>
<!--l. 840--><p class="noindent" >
</p><ol class="enumerate1" >
<li
class="enumerate" id="x1-36003x1">Plot the data as a green-blue polygon instead.
</li>
<li
class="enumerate" id="x1-36005x2">Try using a predefined pattern.
</li></ol>
<a
id="dx1-36006"></a>
<!--l. 849--><p class="noindent" >A common question is : “How can I plot symbols connected by a line with psxy?”. The surprising answer is that we
must call <a
href="../html/man/psxy.html" ><span
class="phvb8t-">psxy</span></a><a
id="dx1-36007"></a> twice. While this sounds cumbersome there is a reason for this: Basically, polygons need to be kept
in memory since they may need to be clipped, hence computer memory places a limit on how large polygons we
may plot. Symbols, on the other hand, can be plotted one at the time so there is no limit to how many
symbols one may plot. Therefore, to connect symbols with a line we must use the overlay approach:
<a
id="dx1-36008"></a>
</p>
<div class="verbatim" id="verbatim-14">
psxy data -R -J -B -P -K -Wthinner > plot.ps
 <br />psxy data -R -J -O -W -Si0.2i >> plot.ps
</div>
<!--l. 862--><p class="nopar" >
</p><!--l. 865--><p class="indent" > Our final <a
href="../html/man/psxy.html" ><span
class="phvb8t-">psxy</span></a><a
id="dx1-36009"></a> example involves a more complicated scenario in which we want to plot the epicenters of
several earthquakes over the background of a coastline basemap. We want the symbols to have a size that reflects
the magnitude of the earthquakes, and that their color should reflect the depth of the hypocenter. You will find the
two files <span class="underline">quakes.ngdc</span> and <span class="underline">quakes.cpt</span> in your directory. The first few lines in the <span class="underline">quakes.ngdc</span> looks like
this:
</p>
<div class="verbatim" id="verbatim-15">
 <br />Historical Tsunami Earthquakes from the NGDC Database
 <br />Year  Mo  Da  Lat+N  Long+E  Dep  Mag
 <br />1987  01  04  49.77  149.29  489  4.1
 <br />1987  01  09  39.90  141.68  067  6.8
</div>
<!--l. 880--><p class="nopar" >
</p><!--l. 883--><p class="indent" > Thus the file has three header records (including the blank line), but we are only interested in columns 5, 4, 6,
and 7. In addition to extract those columns we must also scale the magnitudes into symbols sizes in inches. Given
their range it looks like multiplying the magnitude by 0.02 will work well. Reformatting this file to
comply with the <a
href="../html/man/psxy.html" ><span
class="phvb8t-">psxy</span></a><a
id="dx1-36010"></a> input format can be done in a number of ways, including manual editing, using
MATLAB, a spreadsheet program, or <span
class="ptmri8t-">UNIX</span> tools. Here, without further elaboration, we simply use
the <span
class="ptmri8t-">UNIX</span> tool <span
class="ptmbo8t-">awk</span><a
id="dx1-36011"></a> to do the job ($5 refers to the 5’th column etc., and NR is the current record
number):
</p>
<div class="verbatim" id="verbatim-16">
awk ’{if (NR > 3) print $5, $4, $6, 0.02*$7}’ quakes.ngdc > quakes.d
</div>
<!--l. 896--><p class="nopar" >
</p><!--l. 899--><p class="indent" > The <span
class="ptmbo8t-">awk</span><a
id="dx1-36012"></a> statement is automatically applied to each record, hence the output file <span class="underline">quakes.d</span> should now look like
this (try it!):
</p>
<div class="verbatim" id="verbatim-17">
149.29  49.77  489  0.082
 <br />141.68  39.90  067  0.136
 <br />...etc etc
</div>
<!--l. 906--><p class="nopar" >
</p><!--l. 909--><p class="indent" > We will follow conventional color schemes for seismicity and assign red to shallow quakes (depth
0–100 km), green to intermediate quakes (100–300 km), and blue to deep earthquakes (depth
<!--l. 911--><math
xmlns="http://www.w3.org/1998/Math/MathML"
display="inline" > <mo
class="MathClass-rel">></mo></math> 300
km). The <span class="underline">quakes.cpt</span> file establishes the relationship between depth and color:
</p>
<div class="verbatim" id="verbatim-18">
# color palette for seismicity
 <br />#z0  color   z1 color
 <br />0    red    100 red
 <br />100  green  300 green
 <br />300  blue  1000 blue
</div>
<!--l. 921--><p class="nopar" >
</p><!--l. 924--><p class="indent" > Apart from comment lines (starting with #), each record in the cpt file governs the color of a symbol whose <span
class="ptmri8t-">z </span>value falls in
the range between <!--l. 926--><math
xmlns="http://www.w3.org/1998/Math/MathML"
display="inline" ><msub><mrow
><mi
>z</mi></mrow><mrow
><mn>0</mn></mrow></msub
></math>
and <!--l. 926--><math
xmlns="http://www.w3.org/1998/Math/MathML"
display="inline" ><msub><mrow
><mi
>z</mi></mrow><mrow
><mn>1</mn></mrow></msub
></math>. If
the colors for the lower and upper levels differ then an intermediate color will be linearly interpolated given the
<!--l. 927--><math
xmlns="http://www.w3.org/1998/Math/MathML"
display="inline" ><mi
>z</mi></math> value.
Here, we have chosen constant color intervals.
</p><!--l. 930--><p class="indent" > We may now complete our example using the Mercator projection; we throw in a map scale out of pure
generosity:
</p>
<div class="verbatim" id="verbatim-19">
pscoast -R130/150/35/50 -JM6i -B5 -P -Ggray -Lf134/49/42.5/500 -K > map.ps
 <br />psxy -R -J -O -Cquakes.cpt quakes.d -Sci -Wthinnest >> map.ps
</div>
<!--l. 936--><p class="nopar" >
</p><!--l. 939--><p class="noindent" >where the <span
class="ptmb8t-">i </span>appended to the <span
class="pcrb8t-">-Sc </span>option ensures that symbols sizes are interpreted to be in inches.
</p>
<h4 class="subsectionHead"><span class="titlemark">2.1.3 </span> <a
id="x1-370002.1.3"></a>More exercises</h4>
<!--l. 944--><p class="noindent" >
</p><ol class="enumerate1" >
<li
class="enumerate" id="x1-37002x1">Select another symbol.
</li>
<li
class="enumerate" id="x1-37004x2">Let the deep earthquakes be cyan instead of blue.
</li></ol>
<!--l. 952--><p class="noindent" >
</p>
<h3 class="sectionHead"><span class="titlemark">2.2 </span> <a
id="x1-380002.2"></a>Plotting text strings</h3>
<!--l. 954--><p class="noindent" >In many situations we need to annotate plots or maps with text strings; in <a
href="http://gmt.soest.hawaii.edu" ><span
class="ptmb8t-">GMT</span></a> this is done using <a
href="../html/man/pstext.html" ><span
class="phvb8t-">pstext</span></a><a
id="dx1-38001"></a>. Apart
from the common switches, there are 7 options that are particularly useful (Table <a
href="#x1-38002r4">2.4<!--tex4ht:ref: tbl:pstext --></a>).
</p>
<div class="table">
<!--l. 958--><p class="indent" > <a
id="x1-38002r4"></a></p><hr class="float" /><div class="float"
>
<div class="tabular"> <table id="TBL-6" class="tabular"
cellspacing="0" cellpadding="0" rules="groups"
><colgroup id="TBL-6-1g"><col
id="TBL-6-1" /></colgroup><colgroup id="TBL-6-2g"><col
id="TBL-6-2" /></colgroup><tr
class="hline"><td><hr /></td><td><hr /></td></tr><tr
style="vertical-align:baseline;" id="TBL-6-1-"><td style="text-align:center; white-space:nowrap;" id="TBL-6-1-1"
class="td11"> <div class="multicolumn" style="text-align:center; white-space:nowrap;"><span
class="ptmri8t-x-x-90">Option</span></div> </td><td style="text-align:center; white-space:nowrap;" id="TBL-6-1-2"
class="td11"> <div class="multicolumn" style="text-align:center; white-space:nowrap;"><span
class="ptmri8t-x-x-90">Purpose</span></div>
</td></tr><tr
class="hline"><td><hr /></td><td><hr /></td></tr><tr
style="vertical-align:baseline;" id="TBL-6-2-"><td style="text-align:left; white-space:nowrap;" id="TBL-6-2-1"
class="td11"><span
class="pcrb8t-x-x-90">-C</span><span
class="ptmri8t-x-x-90">dx</span><span
class="ptmr8t-x-x-90">/</span><span
class="ptmri8t-x-x-90">dy </span></td><td style="text-align:left; white-space:nowrap;" id="TBL-6-2-2"
class="td11"><span
class="ptmr8t-x-x-90">Spacing between text and the text box (see </span><span
class="pcrb8t-x-x-90">-W</span><span
class="ptmr8t-x-x-90">) </span></td>
</tr><tr
class="hline"><td><hr /></td><td><hr /></td></tr><tr
style="vertical-align:baseline;" id="TBL-6-3-"><td style="text-align:left; white-space:nowrap;" id="TBL-6-3-1"
class="td11"><span
class="pcrb8t-x-x-90">-D</span><span
class="ptmri8t-x-x-90">dx</span><span
class="ptmr8t-x-x-90">/</span><span
class="ptmri8t-x-x-90">dy </span></td><td style="text-align:left; white-space:nowrap;" id="TBL-6-3-2"
class="td11"><span
class="ptmr8t-x-x-90">Offsets the projected location of the strings </span></td>
</tr><tr
class="hline"><td><hr /></td><td><hr /></td></tr><tr
style="vertical-align:baseline;" id="TBL-6-4-"><td style="text-align:left; white-space:nowrap;" id="TBL-6-4-1"
class="td11"><span
class="pcrb8t-x-x-90">-G</span><span
class="ptmri8t-x-x-90">fill </span></td><td style="text-align:left; white-space:nowrap;" id="TBL-6-4-2"
class="td11"><span
class="ptmr8t-x-x-90">Sets the color of the text </span></td>
</tr><tr
class="hline"><td><hr /></td><td><hr /></td></tr><tr
style="vertical-align:baseline;" id="TBL-6-5-"><td style="text-align:left; white-space:nowrap;" id="TBL-6-5-1"
class="td11"><span
class="pcrb8t-x-x-90">-L </span></td><td style="text-align:left; white-space:nowrap;" id="TBL-6-5-2"
class="td11"><span
class="ptmr8t-x-x-90">Lists the font ids and exits </span></td>
</tr><tr
class="hline"><td><hr /></td><td><hr /></td></tr><tr
style="vertical-align:baseline;" id="TBL-6-6-"><td style="text-align:left; white-space:nowrap;" id="TBL-6-6-1"
class="td11"><span
class="pcrb8t-x-x-90">-N </span></td><td style="text-align:left; white-space:nowrap;" id="TBL-6-6-2"
class="td11"><span
class="ptmr8t-x-x-90">Deactivates clipping at the borders </span></td>
</tr><tr
class="hline"><td><hr /></td><td><hr /></td></tr><tr
style="vertical-align:baseline;" id="TBL-6-7-"><td style="text-align:left; white-space:nowrap;" id="TBL-6-7-1"
class="td11"><span
class="pcrb8t-x-x-90">-S</span><span
class="ptmri8t-x-x-90">pen </span></td><td style="text-align:left; white-space:nowrap;" id="TBL-6-7-2"
class="td11"><span
class="ptmr8t-x-x-90">Selects outline font and sets pen attributes </span></td>
</tr><tr
class="hline"><td><hr /></td><td><hr /></td></tr><tr
style="vertical-align:baseline;" id="TBL-6-8-"><td style="text-align:left; white-space:nowrap;" id="TBL-6-8-1"
class="td11"><span
class="pcrb8t-x-x-90">-W</span><span
class="ptmr8t-x-x-90">[</span><span
class="ptmri8t-x-x-90">fill</span><span
class="ptmr8t-x-x-90">][</span><span
class="ptmb8t-x-x-90">o</span><span
class="ptmr8t-x-x-90">[</span><span
class="ptmri8t-x-x-90">pen</span><span
class="ptmr8t-x-x-90">]]</span></td><td style="text-align:left; white-space:nowrap;" id="TBL-6-8-2"
class="td11"><span
class="ptmr8t-x-x-90">Paint the text box; draw the outline if </span><span
class="ptmb8t-x-x-90">o </span><span
class="ptmr8t-x-x-90">is appended (also see </span><span
class="pcrb8t-x-x-90">-C</span><span
class="ptmr8t-x-x-90">)</span></td>
</tr><tr
class="hline"><td><hr /></td><td><hr /></td></tr><tr
style="vertical-align:baseline;" id="TBL-6-9-"><td style="text-align:left; white-space:nowrap;" id="TBL-6-9-1"
class="td11"> </td></tr></table></div>
<br /><div class="caption"
><span class="id">Table 2.4: </span><span
class="content">Some of the most frequently used options in <a
href="../html/man/pstext.html" ><span
class="phvb8t-">pstext</span></a><a
id="dx1-38003"></a>.</span></div><!--tex4ht:label?: x1-38002r4 -->
</div><hr class="endfloat" />
</div>
<hr class="figure" /><div class="figure"
>
<a
id="x1-38004r1"></a>
<!--l. 975--><p class="noindent" ><img
src="images/GMT_pstext_clearance.png" alt="PIC"
/>
<br /> </p><div class="caption"
><span class="id">Figure 2.1: </span><span
class="content">Relationship between the text box and the extra clearance.</span></div><!--tex4ht:label?: x1-38004r1 -->
</div><hr class="endfigure" />
<!--l. 977--><p class="indent" > The input data to <a
href="../html/man/pstext.html" ><span
class="phvb8t-">pstext</span></a><a
id="dx1-38005"></a> is expected to contain the following information: <br
class="newline" /><a
id="dx1-38006"></a>
</p><!--l. 981--><p class="indent" > <span
class="ptmri8t-">x y size angle fontno justify text </span><br
class="newline" />
</p><!--l. 983--><p class="indent" > The <span
class="ptmri8t-">size </span>argument is the font size in points, the <span
class="ptmri8t-">angle </span>is the angle (measured counterclockwise) between the
text’s baseline and the horizontal, <span
class="ptmri8t-">justify </span>indicates which point on the text-string should correspond to the given <span
class="ptmri8t-">x, y</span>
location, and <span
class="ptmri8t-">text </span>is the text string or sentence to plot. Figure <a
href="#x1-38009r2">2.2<!--tex4ht:ref: fig:GMT_pstext_justify --></a> illustrates these concepts and shows the relevant
two-character codes used for justification. <a
id="dx1-38007"></a><a
id="dx1-38008"></a>
</p>
<hr class="figure" /><div class="figure"
>
<a
id="x1-38009r2"></a>
<!--l. 992--><p class="noindent" ><img
src="images/GMT_pstext_justify.png" alt="PIC"
/>
<br /> </p><div class="caption"
><span class="id">Figure 2.2: </span><span
class="content">Justification (and corresponding character codes) for text strings.</span></div><!--tex4ht:label?: x1-38009r2 -->
</div><hr class="endfigure" />
<!--l. 994--><p class="indent" > The text string can be one or several words and may include octal codes for special characters and
escape-sequences used to select subscripts or symbol fonts. The escape sequences that are recognized by <a
href="http://gmt.soest.hawaii.edu" ><span
class="ptmb8t-">GMT</span></a> are
given in Tables <a
href="#x1-38017r5">2.5<!--tex4ht:ref: tbl:escape --></a> and  <a
href="#x1-38022r6">2.6<!--tex4ht:ref: tbl:scand --></a>. <a
id="dx1-38010"></a><a
id="dx1-38011"></a> <a
id="dx1-38012"></a><a
id="dx1-38013"></a> <a
id="dx1-38014"></a><a
id="dx1-38015"></a> <a
id="dx1-38016"></a>
</p>
<div class="table">
<!--l. 1006--><p class="indent" > <a
id="x1-38017r5"></a></p><hr class="float" /><div class="float"
>
<div class="tabular"> <table id="TBL-7" class="tabular"
cellspacing="0" cellpadding="0" rules="groups"
><colgroup id="TBL-7-1g"><col
id="TBL-7-1" /></colgroup><colgroup id="TBL-7-2g"><col
id="TBL-7-2" /></colgroup><tr
class="hline"><td><hr /></td><td><hr /></td></tr><tr
style="vertical-align:baseline;" id="TBL-7-1-"><td style="text-align:center; white-space:nowrap;" id="TBL-7-1-1"
class="td11"> <div class="multicolumn" style="text-align:center; white-space:nowrap;"><span
class="ptmri8t-x-x-90">Code</span></div> </td><td style="text-align:center; white-space:nowrap;" id="TBL-7-1-2"
class="td11"> <div class="multicolumn" style="text-align:center; white-space:nowrap;"><span
class="ptmri8t-x-x-90">Effect</span></div>
</td></tr><tr
class="hline"><td><hr /></td><td><hr /></td></tr><tr
style="vertical-align:baseline;" id="TBL-7-2-"><td style="text-align:left; white-space:nowrap;" id="TBL-7-2-1"
class="td11"><span
class="ptmr8t-x-x-90">@</span><span
class="ptmr8t-x-x-90">̃ </span></td><td style="text-align:left; white-space:nowrap;" id="TBL-7-2-2"
class="td11"><span
class="ptmr8t-x-x-90">Turns symbol font on or off </span></td>
</tr><tr
class="hline"><td><hr /></td><td><hr /></td></tr><tr
style="vertical-align:baseline;" id="TBL-7-3-"><td style="text-align:left; white-space:nowrap;" id="TBL-7-3-1"
class="td11"><span
class="ptmr8t-x-x-90">@+ </span></td><td style="text-align:left; white-space:nowrap;" id="TBL-7-3-2"
class="td11"><span
class="ptmr8t-x-x-90">Turns superscript on or off </span></td>
</tr><tr
class="hline"><td><hr /></td><td><hr /></td></tr><tr
style="vertical-align:baseline;" id="TBL-7-4-"><td style="text-align:left; white-space:nowrap;" id="TBL-7-4-1"
class="td11"><span
class="ptmr8t-x-x-90">@- </span></td><td style="text-align:left; white-space:nowrap;" id="TBL-7-4-2"
class="td11"><span
class="ptmr8t-x-x-90">Turns subscript on or off </span></td>
</tr><tr
class="hline"><td><hr /></td><td><hr /></td></tr><tr
style="vertical-align:baseline;" id="TBL-7-5-"><td style="text-align:left; white-space:nowrap;" id="TBL-7-5-1"
class="td11"><span
class="ptmr8t-x-x-90">@# </span></td><td style="text-align:left; white-space:nowrap;" id="TBL-7-5-2"
class="td11"><span
class="ptmr8t-x-x-90">Turns small caps on or off </span></td>
</tr><tr
class="hline"><td><hr /></td><td><hr /></td></tr><tr
style="vertical-align:baseline;" id="TBL-7-6-"><td style="text-align:left; white-space:nowrap;" id="TBL-7-6-1"
class="td11"><span
class="ptmr8t-x-x-90">@_ </span></td><td style="text-align:left; white-space:nowrap;" id="TBL-7-6-2"
class="td11"><span
class="ptmr8t-x-x-90">Turns underline on or off </span></td>
</tr><tr
class="hline"><td><hr /></td><td><hr /></td></tr><tr
style="vertical-align:baseline;" id="TBL-7-7-"><td style="text-align:left; white-space:nowrap;" id="TBL-7-7-1"
class="td11"><span
class="ptmr8t-x-x-90">@%</span><span
class="ptmri8t-x-x-90">fontno</span><span
class="ptmr8t-x-x-90">%</span></td><td style="text-align:left; white-space:nowrap;" id="TBL-7-7-2"
class="td11"><span
class="ptmr8t-x-x-90">Switches to another font; @%% resets to previous font </span></td>
</tr><tr
class="hline"><td><hr /></td><td><hr /></td></tr><tr
style="vertical-align:baseline;" id="TBL-7-8-"><td style="text-align:left; white-space:nowrap;" id="TBL-7-8-1"
class="td11"><span
class="ptmr8t-x-x-90">@:</span><span
class="ptmri8t-x-x-90">size</span><span
class="ptmr8t-x-x-90">: </span></td><td style="text-align:left; white-space:nowrap;" id="TBL-7-8-2"
class="td11"><span
class="ptmr8t-x-x-90">Switches to another font size; @:: resets to previous size </span></td>
</tr><tr
class="hline"><td><hr /></td><td><hr /></td></tr><tr
style="vertical-align:baseline;" id="TBL-7-9-"><td style="text-align:left; white-space:nowrap;" id="TBL-7-9-1"
class="td11"><span
class="ptmr8t-x-x-90">@;</span><span
class="ptmri8t-x-x-90">color</span><span
class="ptmr8t-x-x-90">; </span></td><td style="text-align:left; white-space:nowrap;" id="TBL-7-9-2"
class="td11"><span
class="ptmr8t-x-x-90">Switches to another font color; @;; resets to previous color</span></td>
</tr><tr
class="hline"><td><hr /></td><td><hr /></td></tr><tr
style="vertical-align:baseline;" id="TBL-7-10-"><td style="text-align:left; white-space:nowrap;" id="TBL-7-10-1"
class="td11"><span
class="ptmr8t-x-x-90">@! </span></td><td style="text-align:left; white-space:nowrap;" id="TBL-7-10-2"
class="td11"><span
class="ptmr8t-x-x-90">Creates one composite character of the next two characters</span></td>
</tr><tr
class="hline"><td><hr /></td><td><hr /></td></tr><tr
style="vertical-align:baseline;" id="TBL-7-11-"><td style="text-align:left; white-space:nowrap;" id="TBL-7-11-1"
class="td11"><span
class="ptmr8t-x-x-90">@@ </span></td><td style="text-align:left; white-space:nowrap;" id="TBL-7-11-2"
class="td11"><span
class="ptmr8t-x-x-90">Prints the @ sign itself </span></td>
</tr><tr
class="hline"><td><hr /></td><td><hr /></td></tr><tr
style="vertical-align:baseline;" id="TBL-7-12-"><td style="text-align:left; white-space:nowrap;" id="TBL-7-12-1"
class="td11"> </td></tr></table></div>
<br /><div class="caption"
><span class="id">Table 2.5: </span><span
class="content"><a
href="http://gmt.soest.hawaii.edu" ><span
class="ptmb8t-">GMT</span></a> text escape sequences.</span></div><!--tex4ht:label?: x1-38017r5 -->
</div><hr class="endfloat" />
</div>
<!--l. 1026--><p class="indent" > Note that these escape sequences (as well as octal codes) can be used anywhere in <a
href="http://gmt.soest.hawaii.edu" ><span
class="ptmb8t-">GMT</span></a> including in
arguments to the <span
class="pcrb8t-">-B </span>option. A chart of octal codes can be found in Appendix F in the <a
href="http://gmt.soest.hawaii.edu" ><span
class="ptmb8t-">GMT</span></a> technical reference
book. For accented European characters you must set <span
class="ptmb8t-">CHAR_ENCODING </span>to ISOLatin1 in your <span class="underline">.gmtdefaults4</span>
file.
</p><!--l. 1032--><p class="indent" > We will demonstrate <a
href="../html/man/pstext.html" ><span
class="phvb8t-">pstext</span></a><a
id="dx1-38018"></a> with the following script:
</p>
<div class="verbatim" id="verbatim-20">
cat << EOF | pstext -R0/7/0/5 -Jx1i -P -B1g1 -GDarkOrange | gv -
 <br />1  1  30  0  4  BL It’s P@al, not Pal!
 <br />1  2  30  0  4  BL Try @%33%ZapfChancery@%% today
 <br />1  3  30  0  4  BL @~D@~g@-b@- = 2@~pr@~G@~D@~h.
 <br />1  4  30  0  4  BL University of Hawaii at M@!a\225noa
 <br />EOF
</div>
<!--l. 1041--><p class="nopar" >
<a
id="dx1-38019"></a>
</p><!--l. 1046--><p class="indent" > Here we have used the “here document” notation in <span
class="ptmri8t-">UNIX</span>: The
<!--l. 1046--><math
xmlns="http://www.w3.org/1998/Math/MathML"
display="inline" > <mo
class="MathClass-rel"><</mo></math><!--l. 1046--><math
xmlns="http://www.w3.org/1998/Math/MathML"
display="inline" > <mo
class="MathClass-rel"><</mo></math>
EOF will treat the following lines as the input file until it detects the word EOF. We pipe the <span
class="ptmri8t-">PostScript</span> directly
through <span
class="ptmbo8t-">gv</span><a
id="dx1-38020"></a> (the – tells <span
class="ptmbo8t-">gv</span><a
id="dx1-38021"></a> that piping is happening).
</p>
<div class="table">
<!--l. 1051--><p class="indent" > <a
id="x1-38022r6"></a></p><hr class="float" /><div class="float"
>
<div class="tabular"> <table id="TBL-8" class="tabular"
cellspacing="0" cellpadding="0" rules="groups"
><colgroup id="TBL-8-1g"><col
id="TBL-8-1" /></colgroup><colgroup id="TBL-8-2g"><col
id="TBL-8-2" /></colgroup><colgroup id="TBL-8-3g"><col
id="TBL-8-3" /></colgroup><colgroup id="TBL-8-4g"><col
id="TBL-8-4" /></colgroup><tr
class="hline"><td><hr /></td><td><hr /></td><td><hr /></td><td><hr /></td></tr><tr
style="vertical-align:baseline;" id="TBL-8-1-"><td style="text-align:left; white-space:nowrap;" id="TBL-8-1-1"
class="td11"><span
class="ptmri8t-">Code</span></td><td style="text-align:left; white-space:nowrap;" id="TBL-8-1-2"
class="td11"><span
class="ptmri8t-">Effect</span></td><td style="text-align:left; white-space:nowrap;" id="TBL-8-1-3"
class="td11"><span
class="ptmri8t-">Code</span></td><td style="text-align:left; white-space:nowrap;" id="TBL-8-1-4"
class="td11"><span
class="ptmri8t-">Effect</span></td>
</tr><tr
class="hline"><td><hr /></td><td><hr /></td><td><hr /></td><td><hr /></td></tr><tr
style="vertical-align:baseline;" id="TBL-8-2-"><td style="text-align:left; white-space:nowrap;" id="TBL-8-2-1"
class="td11">@E </td><td style="text-align:left; white-space:nowrap;" id="TBL-8-2-2"
class="td11">Æ </td><td style="text-align:left; white-space:nowrap;" id="TBL-8-2-3"
class="td11">@e </td><td style="text-align:left; white-space:nowrap;" id="TBL-8-2-4"
class="td11">æ </td></tr><tr
class="hline"><td><hr /></td><td><hr /></td><td><hr /></td><td><hr /></td></tr><tr
style="vertical-align:baseline;" id="TBL-8-3-"><td style="text-align:left; white-space:nowrap;" id="TBL-8-3-1"
class="td
11">@O </td><td style="text-align:left; white-space:nowrap;" id="TBL-8-3-2"
class="td11">Ø </td><td style="text-align:left; white-space:nowrap;" id="TBL-8-3-3"
class="td11">@o </td><td style="text-align:left; white-space:nowrap;" id="TBL-8-3-4"
class="td11">ø </td>
</tr><tr
class="hline"><td><hr /></td><td><hr /></td><td><hr /></td><td><hr /></td></tr><tr
style="vertical-align:baseline;" id="TBL-8-4-"><td style="text-align:left; white-space:nowrap;" id="TBL-8-4-1"
class="td11">@A </td><td style="text-align:left; white-space:nowrap;" id="TBL-8-4-2"
class="td11">Å </td><td style="text-align:left; white-space:nowrap;" id="TBL-8-4-3"
class="td11">@a </td><td style="text-align:left; white-space:nowrap;" id="TBL-8-4-4"
class="td11">å </td>
</tr><tr
class="hline"><td><hr /></td><td><hr /></td><td><hr /></td><td><hr /></td></tr><tr
style="vertical-align:baseline;" id="TBL-8-5-"><td style="text-align:left; white-space:nowrap;" id="TBL-8-5-1"
class="td11">@C </td><td style="text-align:left; white-space:nowrap;" id="TBL-8-5-2"
class="td11">Ç </td><td style="text-align:left; white-space:nowrap;" id="TBL-8-5-3"
class="td11">@c </td><td style="text-align:left; white-space:nowrap;" id="TBL-8-5-4"
class="td11">ç </td>
</tr><tr
class="hline"><td><hr /></td><td><hr /></td><td><hr /></td><td><hr /></td></tr><tr
style="vertical-align:baseline;" id="TBL-8-6-"><td style="text-align:left; white-space:nowrap;" id="TBL-8-6-1"
class="td11">@N </td><td style="text-align:left; white-space:nowrap;" id="TBL-8-6-2"
class="td11">Ñ </td><td style="text-align:left; white-space:nowrap;" id="TBL-8-6-3"
class="td11">@n </td><td style="text-align:left; white-space:nowrap;" id="TBL-8-6-4"
class="td11">ñ </td>
</tr><tr
class="hline"><td><hr /></td><td><hr /></td><td><hr /></td><td><hr /></td></tr><tr
style="vertical-align:baseline;" id="TBL-8-7-"><td style="text-align:left; white-space:nowrap;" id="TBL-8-7-1"
class="td11">@U </td><td style="text-align:left; white-space:nowrap;" id="TBL-8-7-2"
class="td11">Ü </td><td style="text-align:left; white-space:nowrap;" id="TBL-8-7-3"
class="td11">@u </td><td style="text-align:left; white-space:nowrap;" id="TBL-8-7-4"
class="td11">ü </td>
</tr><tr
class="hline"><td><hr /></td><td><hr /></td><td><hr /></td><td><hr /></td></tr><tr
style="vertical-align:baseline;" id="TBL-8-8-"><td style="text-align:left; white-space:nowrap;" id="TBL-8-8-1"
class="td11">@s </td><td style="text-align:left; white-space:nowrap;" id="TBL-8-8-2"
class="td11">ß </td><td style="text-align:left; white-space:nowrap;" id="TBL-8-8-3"
class="td11"> </td><td style="text-align:left; white-space:nowrap;" id="TBL-8-8-4"
class="td11"> </td>
</tr><tr
class="hline"><td><hr /></td><td><hr /></td><td><hr /></td><td><hr /></td></tr><tr
style="vertical-align:baseline;" id="TBL-8-9-"><td style="text-align:left; white-space:nowrap;" id="TBL-8-9-1"
class="td11"> </td></tr></table></div>
<br /><div class="caption"
><span class="id">Table 2.6: </span><span
class="content">Shortcuts for some European characters.</span></div><!--tex4ht:label?: x1-38022r6 -->
</div><hr class="endfloat" />
</div>
<h3 class="sectionHead"><span class="titlemark">2.3 </span> <a
id="x1-390002.3"></a>Exercises</h3>
<a
id="dx1-39001"></a>
<!--l. 1070--><p class="noindent" >
</p><ol class="enumerate1" >
<li
class="enumerate" id="x1-39003x1">At <!--l. 1072--><math
xmlns="http://www.w3.org/1998/Math/MathML"
display="inline" ><mi
>y</mi> <mo
class="MathClass-rel">=</mo> <mn>5</mn></math>,
add the sentence “<!--l. 1072--><math
xmlns="http://www.w3.org/1998/Math/MathML"
display="inline" ><msup><mrow
><mi
>z</mi></mrow><mrow
><mn>2</mn></mrow></msup
> <mo
class="MathClass-rel">=</mo> <msup><mrow
><mi
>x</mi></mrow><mrow
><mn>2</mn></mrow></msup
> <mo
class="MathClass-bin">+</mo><msup><mrow
><mi
>y</mi></mrow><mrow
><mn>2</mn></mrow></msup
></math>”.
</li>
<li
class="enumerate" id="x1-39005x2">At <!--l. 1074--><math
xmlns="http://www.w3.org/1998/Math/MathML"
display="inline" ><mi
>y</mi> <mo
class="MathClass-rel">=</mo> <mn>6</mn></math>,
add the sentence “It is 80<span
class="ptmr8c-">°</span> today”.
</li></ol>
<a
id="dx1-39006"></a>
<h2 class="chapterHead"><span class="titlemark">Chapter 3</span><br /><a
id="x1-400003"></a>SESSION THREE</h2>
<h3 class="sectionHead"><span class="titlemark">3.1 </span> <a
id="x1-410003.1"></a>Contouring gridded data sets</h3>
<!--l. 1084--><p class="noindent" ><a
href="http://gmt.soest.hawaii.edu" ><span
class="ptmb8t-">GMT</span></a> comes with several utilities that can create gridded data sets; we will discuss two such programs
later this session. First, we will assume that we already have gridded data sets. In the supplemental
<a
href="http://gmt.soest.hawaii.edu" ><span
class="ptmb8t-">GMT</span></a> archive there is a program that serves as a data extractor from several public domain global
gridded data sets. Among these data are ETOPO5, crustal ages, gravity and geoid, and DEM for the
continental US. Here, we will use <a
href="../html/man/grdraster.html" ><span
class="phvb8t-">grdraster</span></a><a
id="dx1-41001"></a> to extract a <a
href="http://gmt.soest.hawaii.edu" ><span
class="ptmb8t-">GMT</span></a>-ready grid that we will next use for
contouring:
</p>
<div class="verbatim" id="verbatim-21">
grdraster 1 -R-66/-60/30/35 -Gbermuda.nc -V
</div>
<!--l. 1095--><p class="nopar" >
</p><!--l. 1098--><p class="indent" > Here we use the file extension <span class="underline">.nc</span> instead of the generic <span class="underline">.grd</span> to indicate that this is a netCDF file. It is good
form, but not essential, to use <span class="underline">.nc</span> for netCDF grids. Using that extension will help other programs installed on your
system to recognize these files and might give it an identifiable icon in your file browser. Learn about other
programs that read netCDF files at the <a
href="http://www.unidata.ucar.edu/software/netcdf/" >netCDF website</a> You can find <span class="underline">bermuda.nc</span> also in the <span class="underline">tutorial</span>
directory of you <a
href="http://gmt.soest.hawaii.edu" ><span
class="ptmb8t-">GMT</span></a> installation. Feel free to open it in any other program and compare results with
<a
href="http://gmt.soest.hawaii.edu" ><span
class="ptmb8t-">GMT</span></a>.
</p><!--l. 1108--><p class="indent" > We first use the <a
href="http://gmt.soest.hawaii.edu" ><span
class="ptmb8t-">GMT</span></a> program <a
href="../html/man/grdinfo.html" ><span
class="phvb8t-">grdinfo</span></a><a
id="dx1-41002"></a> to see what’s in this file:
</p>
<div class="verbatim" id="verbatim-22">
grdinfo bermuda.nc
</div>
<!--l. 1112--><p class="nopar" >
</p><!--l. 1115--><p class="indent" > The file contains bathymetry for the Bermuda region and has depth values from -5475 to -89 meters. We want
to make a contour map of this data; this is a job for <a
href="../html/man/grdcontour.html" ><span
class="phvb8t-">grdcontour</span></a><a
id="dx1-41003"></a>. As with previous plot commands we need to set
up the map projection with <span
class="pcrb8t-">-J</span>. Here, however, we do not have to specify the region since that is by default
assumed to be the extent of the grid file. To generate any plot we will in addition need to supply information
about which contours to draw. Unfortunately, <a
href="../html/man/grdcontour.html" ><span
class="phvb8t-">grdcontour</span></a><a
id="dx1-41004"></a> is a complicated program with too many
options. We put a positive spin on this situation by touting its flexibility. Here are the most useful
options:
</p>
<div class="table">
<!--l. 1127--><p class="indent" > <a
id="x1-41005r1"></a></p><hr class="float" /><div class="float"
>
<div class="tabular"> <table id="TBL-9" class="tabular"
cellspacing="0" cellpadding="0" rules="groups"
><colgroup id="TBL-9-1g"><col
id="TBL-9-1" /></colgroup><colgroup id="TBL-9-2g"><col
id="TBL-9-2" /></colgroup><tr
class="hline"><td><hr /></td><td><hr /></td></tr><tr
style="vertical-align:baseline;" id="TBL-9-1-"><td style="text-align:center; white-space:nowrap;" id="TBL-9-1-1"
class="td11"> <div class="multicolumn" style="text-align:center; white-space:nowrap;"><span
class="ptmri8t-x-x-90">Option</span></div> </td><td style="text-align:center; white-space:nowrap;" id="TBL-9-1-2"
class="td11"> <div class="multicolumn" style="text-align:center; white-space:nowrap;"><span
class="ptmri8t-x-x-90">Purpose</span></div>
</td></tr><tr
class="hline"><td><hr /></td><td><hr /></td></tr><tr
style="vertical-align:baseline;" id="TBL-9-2-"><td style="text-align:left; white-space:nowrap;" id="TBL-9-2-1"
class="td11"><span
class="pcrb8t-x-x-90">-A</span><span
class="ptmri8t-x-x-90">annot_int </span></td><td style="text-align:left; white-space:nowrap;" id="TBL-9-2-2"
class="td11"><span
class="ptmr8t-x-x-90">Annotation interval and attributes </span></td>
</tr><tr
class="hline"><td><hr /></td><td><hr /></td></tr><tr
style="vertical-align:baseline;" id="TBL-9-3-"><td style="text-align:left; white-space:nowrap;" id="TBL-9-3-1"
class="td11"><span
class="pcrb8t-x-x-90">-C</span><span
class="ptmri8t-x-x-90">cont_int </span></td><td style="text-align:left; white-space:nowrap;" id="TBL-9-3-2"
class="td11"><span
class="ptmr8t-x-x-90">Contour interval </span></td>
</tr><tr
class="hline"><td><hr /></td><td><hr /></td></tr><tr
style="vertical-align:baseline;" id="TBL-9-4-"><td style="text-align:left; white-space:nowrap;" id="TBL-9-4-1"
class="td11"><span
class="pcrb8t-x-x-90">-G</span><span
class="ptmri8t-x-x-90">gap </span></td><td style="text-align:left; white-space:nowrap;" id="TBL-9-4-2"
class="td11"><span
class="ptmr8t-x-x-90">Controls placement of contour annotations </span></td>
</tr><tr
class="hline"><td><hr /></td><td><hr /></td></tr><tr
style="vertical-align:baseline;" id="TBL-9-5-"><td style="text-align:left; white-space:nowrap;" id="TBL-9-5-1"
class="td11"><span
class="pcrb8t-x-x-90">-L</span><span
class="ptmri8t-x-x-90">low</span><span
class="ptmr8t-x-x-90">/</span><span
class="ptmri8t-x-x-90">high </span></td><td style="text-align:left; white-space:nowrap;" id="TBL-9-5-2"
class="td11"><span
class="ptmr8t-x-x-90">Only draw contours within the </span><span
class="ptmri8t-x-x-90">low </span><span
class="ptmr8t-x-x-90">to </span><span
class="ptmri8t-x-x-90">high </span><span
class="ptmr8t-x-x-90">range </span></td>
</tr><tr
class="hline"><td><hr /></td><td><hr /></td></tr><tr
style="vertical-align:baseline;" id="TBL-9-6-"><td style="text-align:left; white-space:nowrap;" id="TBL-9-6-1"
class="td11"><span
class="pcrb8t-x-x-90">-Q</span><span
class="ptmri8t-x-x-90">cut </span></td><td style="text-align:left; white-space:nowrap;" id="TBL-9-6-2"
class="td11"><span
class="ptmr8t-x-x-90">Do not draw contours with fewer than </span><span
class="ptmri8t-x-x-90">cut </span><span
class="ptmr8t-x-x-90">points </span></td>
</tr><tr
class="hline"><td><hr /></td><td><hr /></td></tr><tr
style="vertical-align:baseline;" id="TBL-9-7-"><td style="text-align:left; white-space:nowrap;" id="TBL-9-7-1"
class="td11"><span
class="pcrb8t-x-x-90">-S</span><span
class="ptmri8t-x-x-90">smooth </span></td><td style="text-align:left; white-space:nowrap;" id="TBL-9-7-2"
class="td11"><span
class="ptmr8t-x-x-90">Resample contours every </span><span
class="ptmri8t-x-x-90">x_inc</span><span
class="ptmr8t-x-x-90">/</span><span
class="ptmri8t-x-x-90">smooth </span><span
class="ptmr8t-x-x-90">increment </span></td>
</tr><tr
class="hline"><td><hr /></td><td><hr /></td></tr><tr
style="vertical-align:baseline;" id="TBL-9-8-"><td style="text-align:left; white-space:nowrap;" id="TBL-9-8-1"
class="td11"><span
class="pcrb8t-x-x-90">-T</span><span
class="ptmr8t-x-x-90">[</span><span
class="ptmb8t-x-x-90">+</span><!--l. 1138--><math
xmlns="http://www.w3.org/1998/Math/MathML"
display="inline" ><mo
class="MathClass-rel">|</mo></math><span
class="ptmb8t-x-x-90">-</span><span
class="ptmr8t-x-x-90">][</span><span
class="ptmri8t-x-x-90">gap</span><span
class="ptmr8t-x-x-90">/</span><span
class="ptmri8t-x-x-90">length</span><span
class="ptmr8t-x-x-90">][:</span><span
class="ptmri8t-x-x-90">LH</span><span
class="ptmr8t-x-x-90">]</span></td><td style="text-align:left; white-space:nowrap;" id="TBL-9-8-2"
class="td11"><span
class="ptmr8t-x-x-90">Draw tick-marks in downhill direction for innermost closed contours </span></td>
</tr><tr
class="hline"><td><hr /></td><td><hr /></td></tr><tr
style="vertical-align:baseline;" id="TBL-9-9-"><td style="text-align:left; white-space:nowrap;" id="TBL-9-9-1"
class="td11"> </td><td style="text-align:left; white-space:nowrap;" id="TBL-9-9-2"
class="td11"><span
class="ptmr8t-x-x-90">Add tick spacing and length, and characters to plot at the center of closed contours.</span></td>
</tr><tr
class="hline"><td><hr /></td><td><hr /></td></tr><tr
style="vertical-align:baseline;" id="TBL-9-10-"><td style="text-align:left; white-space:nowrap;" id="TBL-9-10-1"
class="td11"><span
class="pcrb8t-x-x-90">-W</span><span
class="ptmr8t-x-x-90">[</span><span
class="ptmb8t-x-x-90">a</span><!--l. 1140--><math
xmlns="http://www.w3.org/1998/Math/MathML"
display="inline" ><mo
class="MathClass-rel">|</mo></math><span
class="ptmb8t-x-x-90">c</span><span
class="ptmr8t-x-x-90">]</span><span
class="ptmri8t-x-x-90">pen </span></td><td style="text-align:left; white-space:nowrap;" id="TBL-9-10-2"
class="td11"><span
class="ptmr8t-x-x-90">Set contour and annotation pens </span></td>
</tr><tr
class="hline"><td><hr /></td><td><hr /></td></tr><tr
style="vertical-align:baseline;" id="TBL-9-11-"><td style="text-align:left; white-space:nowrap;" id="TBL-9-11-1"
class="td11"><span
class="pcrb8t-x-x-90">-Z</span><span
class="ptmri8t-x-x-90">factor</span><span
class="ptmr8t-x-x-90">[/</span><span
class="ptmri8t-x-x-90">offset</span><span
class="ptmr8t-x-x-90">] </span></td><td style="text-align:left; white-space:nowrap;" id="TBL-9-11-2"
class="td11"><span
class="ptmr8t-x-x-90">[Subtract </span><span
class="ptmri8t-x-x-90">offset</span><span
class="ptmr8t-x-x-90">] and multiply data by </span><span
class="ptmri8t-x-x-90">factor </span><span
class="ptmr8t-x-x-90">prior to processing </span></td>
</tr><tr
class="hline"><td><hr /></td><td><hr /></td></tr><tr
style="vertical-align:baseline;" id="TBL-9-12-"><td style="text-align:left; white-space:nowrap;" id="TBL-9-12-1"
class="td11"> </td></tr></table>
</div>
<br /><div class="caption"
><span class="id">Table 3.1: </span><span
class="content">The most useful options in <a
href="../html/man/grdcontour.html" ><span
class="phvb8t-">grdcontour</span></a><a
id="dx1-41006"></a>.</span></div><!--tex4ht:label?: x1-41005r1 -->
</div><hr class="endfloat" />
</div>
<!--l. 1147--><p class="indent" > We will first make a plain contour map using 1 km as annotation interval and 250 m as contour interval. We
choose a 7-inch-wide Mercator plot and annotate the borders every 2<span
class="ptmr8c-">°</span>:
</p>
<div class="verbatim" id="verbatim-23">
grdcontour bermuda.nc -JM7i -C250 -A1000 -P -B2 | gv -
</div>
<!--l. 1153--><p class="nopar" >
</p>
<h4 class="subsectionHead"><span class="titlemark">3.1.1 </span> <a
id="x1-420003.1.1"></a>Exercises</h4>
<a
id="dx1-42001"></a>
<!--l. 1159--><p class="noindent" >
</p><ol class="enumerate1" >
<li
class="enumerate" id="x1-42003x1">Add smoothing with <span
class="pcrb8t-">-S</span>4.
</li>
<li
class="enumerate" id="x1-42005x2">Try tick all highs and lows with <span
class="pcrb8t-">-T</span>.
</li>
<li
class="enumerate" id="x1-42007x3">Skip small features with <span
class="pcrb8t-">-Q</span>10.
</li>
<li
class="enumerate" id="x1-42009x4">Override region using <span
class="pcrb8t-">-R</span>-70/-60/25/35.
</li>
<li
class="enumerate" id="x1-42011x5">Try another region that clips our data domain.
</li>
<li
class="enumerate" id="x1-42013x6">Scale data to km and use the km unit in the annotations.
</li></ol>
<a
id="dx1-42014"></a>
<!--l. 1176--><p class="noindent" >
</p>
<h3 class="sectionHead"><span class="titlemark">3.2 </span> <a
id="x1-430003.2"></a>Gridding of arbitrarily spaced data</h3>
<!--l. 1178--><p class="noindent" >Except in the situation above when a grid file is available, we must convert our data to the right format readable
by <a
href="http://gmt.soest.hawaii.edu" ><span
class="ptmb8t-">GMT</span></a> before we can make contour plots and color-coded images. We distinguish between two
scenarios:
</p><!--l. 1183--><p class="indent" >
</p><ol class="enumerate1" >
<li
class="enumerate" id="x1-43002x1">The (<span
class="ptmri8t-">x</span>, <span
class="ptmri8t-">y</span>, <span
class="ptmri8t-">z</span>) data are available on a regular lattice grid.
</li>
<li
class="enumerate" id="x1-43004x2">The (<span
class="ptmri8t-">x</span>, <span
class="ptmri8t-">y</span>, <span
class="ptmri8t-">z</span>) data are distributed unevenly in the plane.
</li></ol>
<!--l. 1193--><p class="indent" > The former situation may require a simple reformatting (using <a
href="../html/man/xyz2grd.html" ><span
class="phvb8t-">xyz2grd</span></a><a
id="dx1-43005"></a>), while the latter must be interpolated
onto a regular lattice; this process is known as gridding. <a
href="http://gmt.soest.hawaii.edu" ><span
class="ptmb8t-">GMT</span></a> supports three different approaches to gridding;
here, we will briefly discuss the two most common techniques.
</p><!--l. 1200--><p class="indent" > All <a
href="http://gmt.soest.hawaii.edu" ><span
class="ptmb8t-">GMT</span></a> gridding programs have in common the requirement that the user must specify the grid domain and
output filename: <br
class="newline" />
</p>
<div class="tabular"> <table id="TBL-10" class="tabular"
cellspacing="0" cellpadding="0"
><colgroup id="TBL-10-1g"><col
id="TBL-10-1" /><col
id="TBL-10-2" /></colgroup><tr
style="vertical-align:baseline;" id="TBL-10-1-"><td style="text-align:left; white-space:nowrap;" id="TBL-10-1-1"
class="td11"><span
class="pcrb8t-">-R</span><span
class="ptmri8t-">xmin</span>/<span
class="ptmri8t-">xmax</span>/<span
class="ptmri8t-">ymin</span>/<span
class="ptmri8t-">ymax </span></td><td style="text-align:left; white-space:nowrap;" id="TBL-10-1-2"
class="td11">The desired grid extent </td>
</tr><tr
style="vertical-align:baseline;" id="TBL-10-2-"><td style="text-align:left; white-space:nowrap;" id="TBL-10-2-1"
class="td11"><span
class="pcrb8t-">-I</span><span
class="ptmri8t-">xinc</span>[<span
class="ptmb8t-">m</span><!--l. 1205--><math
xmlns="http://www.w3.org/1998/Math/MathML"
display="inline" ><mo
class="MathClass-rel">|</mo></math><span
class="ptmb8t-">c</span>][/<span
class="ptmri8t-">yinc</span>[<span
class="ptmb8t-">m</span><!--l. 1205--><math
xmlns="http://www.w3.org/1998/Math/MathML"
display="inline" ><mo
class="MathClass-rel">|</mo></math><span
class="ptmb8t-">c</span>]]</td><td style="text-align:left; white-space:nowrap;" id="TBL-10-2-2"
class="td11">The grid spacing (append <span
class="ptmb8t-">m </span>or <span
class="ptmb8t-">c </span>for minutes or seconds of arc)</td>
</tr><tr
style="vertical-align:baseline;" id="TBL-10-3-"><td style="text-align:left; white-space:nowrap;" id="TBL-10-3-1"
class="td11"><span
class="pcrb8t-">-G</span><span
class="ptmri8t-">gridfile </span></td><td style="text-align:left; white-space:nowrap;" id="TBL-10-3-2"
class="td11">The output grid filename </td>
</tr><tr
style="vertical-align:baseline;" id="TBL-10-4-"><td style="text-align:left; white-space:nowrap;" id="TBL-10-4-1"
class="td11"> </td> </tr></table>
</div>
<!--l. 1209--><p class="noindent" >
</p>
<h4 class="subsectionHead"><span class="titlemark">3.2.1 </span> <a
id="x1-440003.2.1"></a>Nearest neighbor gridding</h4>
<hr class="figure" /><div class="figure"
>
<a
id="x1-44001r1"></a>
<!--l. 1211--><p class="noindent" ><img
src="images/GMT_nearneighbor.png" alt="PIC"
/>
<br /> </p><div class="caption"
><span class="id">Figure 3.1: </span><span
class="content">Search geometry for <a
href="../html/man/nearneighbor.html" ><span
class="phvb8t-">nearneighbor</span></a><a
id="dx1-44002"></a>.</span></div><!--tex4ht:label?: x1-44001r1 -->
</div><hr class="endfigure" />
<!--l. 1213--><p class="indent" > The <a
href="http://gmt.soest.hawaii.edu" ><span
class="ptmb8t-">GMT</span></a> program <a
href="../html/man/nearneighbor.html" ><span
class="phvb8t-">nearneighbor</span></a><a
id="dx1-44003"></a> implements a simple “nearest neighbor” averaging operation. It is the
preferred way to grid data when the data density is high. <a
href="../html/man/nearneighbor.html" ><span
class="phvb8t-">nearneighbor</span></a><a
id="dx1-44004"></a> is a local procedure which means it will
only consider the control data that is close to the desired output grid node. Only data points inside a specified
search radius will be used, and we may also impose the condition that each of the <span
class="ptmri8t-">n </span>sectors must have at least one
data point in order to assign the nodal value. The nodal value is computed as a weighted average of the nearest data
point per sector inside the search radius, with each point weighted according to its distance from the node as
follows:
</p>
<div class="par-math-display"><!--l. 1225--><math
xmlns="http://www.w3.org/1998/Math/MathML"
display="block" ><mrow
>
<mover
accent="true"><mrow
><mi
>z</mi></mrow><mo
class="MathClass-op">̄</mo></mover> <mo
class="MathClass-rel">=</mo> <mfrac><mrow
><munderover accentunder="false" accent="false"><mrow
><mo mathsize="big"
>∑</mo></mrow><mrow
><mi
>i</mi><mo
class="MathClass-rel">=</mo><mn>1</mn></mrow><mrow
><mi
>n</mi></mrow></munderover
><msub><mrow
><mi
>z</mi></mrow><mrow
><mi
>i</mi></mrow></msub
><msub><mrow
><mi
>w</mi></mrow><mrow
><mi
>i</mi></mrow></msub
></mrow>
<mrow
><munderover accentunder="false" accent="false"><mrow
><mo mathsize="big"
>∑</mo></mrow><mrow
><mi
>i</mi><mo
class="MathClass-rel">=</mo><mn>1</mn></mrow><mrow
><mi
>n</mi></mrow></munderover
><msub><mrow
><mi
>w</mi></mrow><mrow
><mi
>i</mi></mrow></msub
></mrow></mfrac> <mspace width="1em" class="quad"/><msub><mrow
><mi
>w</mi></mrow><mrow
><mi
>i</mi></mrow></msub
> <mo
class="MathClass-rel">=</mo><msup><mrow
> <mfenced separators=""
open="(" close=")" ><mrow><mn>1</mn><mo
class="MathClass-bin">+</mo> <mfrac><mrow
><mn>9</mn><msubsup><mrow
><mi
>r</mi></mrow><mrow
><mi
>i</mi></mrow><mrow
><mn>2</mn></mrow></msubsup
></mrow>
<mrow
><msup><mrow
><mi
>R</mi></mrow><mrow
><mn>2</mn></mrow></msup
></mrow></mfrac> </mrow></mfenced></mrow><mrow
><mo
class="MathClass-bin">-</mo><mn>1</mn></mrow></msup
>
</mrow></math></div>
<!--l. 1228--><p class="nopar" >
<a
id="dx1-44005"></a>
</p><!--l. 1232--><p class="noindent" >The most important switches are listed in Table <a
href="#x1-44006r2">3.2<!--tex4ht:ref: tbl:nearneighbor --></a>.
</p>
<div class="table">
<!--l. 1235--><p class="indent" > <a
id="x1-44006r2"></a></p><hr class="float" /><div class="float"
>
<div class="tabular"> <table id="TBL-11" class="tabular"
cellspacing="0" cellpadding="0" rules="groups"
><colgroup id="TBL-11-1g"><col
id="TBL-11-1" /></colgroup><colgroup id="TBL-11-2g"><col
id="TBL-11-2" /></colgroup><tr
class="hline"><td><hr /></td><td><hr /></td></tr><tr
style="vertical-align:baseline;" id="TBL-11-1-"><td style="text-align:center; white-space:nowrap;" id="TBL-11-1-1"
class="td11"> <div class="multicolumn" style="text-align:center; white-space:nowrap;"><span
class="ptmri8t-x-x-90">Option</span></div> </td><td style="text-align:center; white-space:nowrap;" id="TBL-11-1-2"
class="td11"> <div class="multicolumn" style="text-align:center; white-space:nowrap;"><span
class="ptmri8t-x-x-90">Purpose</span></div>
</td></tr><tr
class="hline"><td><hr /></td><td><hr /></td></tr><tr
style="vertical-align:baseline;" id="TBL-11-2-"><td style="text-align:left; white-space:nowrap;" id="TBL-11-2-1"
class="td11"><span
class="pcrb8t-x-x-90">-S</span><span
class="ptmri8t-x-x-90">radius</span><span
class="ptmr8t-x-x-90">[</span><span
class="ptmb8t-x-x-90">k</span><span
class="ptmr8t-x-x-90">]</span></td><td style="text-align:left; white-space:nowrap;" id="TBL-11-2-2"
class="td11"><span
class="ptmr8t-x-x-90">Sets search radius. Append </span><span
class="ptmb8t-x-x-90">k </span><span
class="ptmr8t-x-x-90">to indicate radius in kilometers [Default is </span><span
class="ptmri8t-x-x-90">x</span><span
class="ptmr8t-x-x-90">-units]</span></td>
</tr><tr
class="hline"><td><hr /></td><td><hr /></td></tr><tr
style="vertical-align:baseline;" id="TBL-11-3-"><td style="text-align:left; white-space:nowrap;" id="TBL-11-3-1"
class="td11"><span
class="pcrb8t-x-x-90">-E</span><span
class="ptmri8t-x-x-90">empty </span></td><td style="text-align:left; white-space:nowrap;" id="TBL-11-3-2"
class="td11"><span
class="ptmr8t-x-x-90">Assign this value to unconstrained nodes [Default is NaN] </span></td>
</tr><tr
class="hline"><td><hr /></td><td><hr /></td></tr><tr
style="vertical-align:baseline;" id="TBL-11-4-"><td style="text-align:left; white-space:nowrap;" id="TBL-11-4-1"
class="td11"><span
class="pcrb8t-x-x-90">-N</span><span
class="ptmri8t-x-x-90">sectors </span></td><td style="text-align:left; white-space:nowrap;" id="TBL-11-4-2"
class="td11"><span
class="ptmr8t-x-x-90">Sector search, indicate number of sectors [Default is 4] </span></td>
</tr><tr
class="hline"><td><hr /></td><td><hr /></td></tr><tr
style="vertical-align:baseline;" id="TBL-11-5-"><td style="text-align:left; white-space:nowrap;" id="TBL-11-5-1"
class="td11"><span
class="pcrb8t-x-x-90">-W </span></td><td style="text-align:left; white-space:nowrap;" id="TBL-11-5-2"
class="td11"><span
class="ptmr8t-x-x-90">Read relative weights from the 4th column of input data </span></td>
</tr><tr
class="hline"><td><hr /></td><td><hr /></td></tr><tr
style="vertical-align:baseline;" id="TBL-11-6-"><td style="text-align:left; white-space:nowrap;" id="TBL-11-6-1"
class="td11"> </td></tr></table></div>
<br /><div class="caption"
><span class="id">Table 3.2: </span><span
class="content">Switches used with the <a
href="../html/man/nearneighbor.html" ><span
class="phvb8t-">nearneighbor</span></a><a
id="dx1-44007"></a> program.</span></div><!--tex4ht:label?: x1-44006r2 -->
</div><hr class="endfloat" />
</div>
<!--l. 1249--><p class="indent" > We will grid the data in the file <span class="underline">ship.xyz</span> which contains ship observations of bathymetry off Baja California.
You can find the file in the sub-directory for example 15. We desire to make a 5’ by 5’ grid. Running <a
href="../html/man/minmax.html" ><span
class="phvb8t-">minmax</span></a><a
id="dx1-44008"></a> on
the file yields
</p>
<div class="verbatim" id="verbatim-24">
ship.xyz: N = 82970     <245/254.705>   <20/29.99131>   <-7708/-9>
</div>
<!--l. 1256--><p class="nopar" >
</p><!--l. 1259--><p class="indent" > so we choose the region accordingly:
</p>
<div class="verbatim" id="verbatim-25">
nearneighbor -R245/255/20/30 -I5m -S40k -Gship.nc -V ship.xyz
</div>
<!--l. 1263--><p class="nopar" >
</p><!--l. 1266--><p class="indent" > We may get a view of the contour map using
</p>
<div class="verbatim" id="verbatim-26">
grdcontour ship.nc -JM6i -P -B2 -C250 -A1000 | gv -
</div>
<!--l. 1270--><p class="nopar" >
</p><!--l. 1273--><p class="indent" > Since the grid <span class="underline">ship.nc</span> is stored in netCDF format that is supported by a host of other programs, you can try one
of those as well on the same grid.
</p>
<h5 class="subsubsectionHead"><a
id="x1-450003.2.1"></a>Exercises</h5>
<a
id="dx1-45001"></a>
<!--l. 1279--><p class="noindent" >
</p><ol class="enumerate1" >
<li
class="enumerate" id="x1-45003x1">Try using a 100 km search radius and a 10 minute grid spacing.
</li></ol>
<a
id="dx1-45004"></a>
<!--l. 1286--><p class="noindent" >
</p>
<h4 class="subsectionHead"><span class="titlemark">3.2.2 </span> <a
id="x1-460003.2.2"></a>Gridding with Splines in Tension</h4>
<!--l. 1288--><p class="noindent" >As an alternative, we may use a global procedure to grid our data. This approach, implemented in the program
<a
href="../html/man/surface.html" ><span
class="phvb8t-">surface</span></a><a
id="dx1-46001"></a>, represents an improvement over standard minimum curvature algorithms by allowing users to introduce
some tension into the surface. Physically, we are trying to force a thin elastic plate to go through all our data points;
the values of this surface at the grid points become the gridded data. Mathematically, we want to find the function
<!--l. 1295--><math
xmlns="http://www.w3.org/1998/Math/MathML"
display="inline" ><mi
>z</mi><mrow ><mo
class="MathClass-open">(</mo><mrow><mi
>x</mi><mo
class="MathClass-punc">,</mo><mi
>y</mi></mrow><mo
class="MathClass-close">)</mo></mrow></math> that
satisfies the following constraints: <br
class="newline" /><a
id="dx1-46002"></a>
</p><!--l. 1298--><p class="indent" > <!--l. 1298--><math
xmlns="http://www.w3.org/1998/Math/MathML"
display="inline" ><mrow
> <mtable style="text-align:axis;"
equalrows="false" columnlines="none" equalcolumns="false" class="array"><mtr><mtd
class="array" columnalign="left"><mi
>z</mi><mrow ><mo
class="MathClass-open">(</mo><mrow><msub><mrow
><mi
>x</mi></mrow><mrow
><mi
>k</mi></mrow></msub
><mo
class="MathClass-punc">,</mo><msub><mrow
><mi
>y</mi></mrow><mrow
><mi
>k</mi></mrow></msub
></mrow><mo
class="MathClass-close">)</mo></mrow> <mo
class="MathClass-rel">=</mo> <msub><mrow
><mi
>z</mi></mrow><mrow
><mi
>k</mi></mrow></msub
><mo
class="MathClass-punc">,</mo> </mtd><mtd
class="array" columnalign="left"><mstyle
class="mbox"><mtext >for all data </mtext><mstyle
class="math"><mrow ><mo
class="MathClass-open">(</mo><mrow><msub><mrow
><mi
>x</mi></mrow><mrow
><mi
>k</mi></mrow></msub
><mo
class="MathClass-punc">,</mo><msub><mrow
><mi
>y</mi></mrow><mrow
><mi
>k</mi></mrow></msub
><mo
class="MathClass-punc">,</mo><msub><mrow
><mi
>z</mi></mrow><mrow
><mi
>k</mi></mrow></msub
></mrow><mo
class="MathClass-close">)</mo></mrow><mo
class="MathClass-punc">,</mo><mi
>k</mi> <mo
class="MathClass-rel">=</mo> <mn>1</mn><mo
class="MathClass-punc">,</mo><mi
>n</mi></mstyle><mtext ></mtext></mstyle></mtd>
</mtr><mtr><mtd
class="array" columnalign="left"><mrow ><mo
class="MathClass-open">(</mo><mrow><mn>1</mn><mo
class="MathClass-bin">-</mo><mi
>t</mi></mrow><mo
class="MathClass-close">)</mo></mrow><msup><mrow
><mo
class="MathClass-op">∇</mo></mrow><mrow
><mn>4</mn></mrow></msup
><mi
>z</mi><mo
class="MathClass-bin">-</mo><mi
>t</mi><msup><mrow
><mo
class="MathClass-op">∇</mo></mrow><mrow
><mn>2</mn></mrow></msup
><mi
>z</mi> <mo
class="MathClass-rel">=</mo> <mn>0</mn></mtd><mtd
class="array" columnalign="left"><mstyle
class="mbox"><mtext >elsewhere</mtext></mstyle> </mtd></mtr> <!--ll--></mtable> </mrow></math>
<br
class="newline" />
</p><!--l. 1303--><p class="noindent" >where <!--l. 1304--><math
xmlns="http://www.w3.org/1998/Math/MathML"
display="inline" ><mi
>t</mi></math> is the “tension”,
<!--l. 1304--><math
xmlns="http://www.w3.org/1998/Math/MathML"
display="inline" ><mn>0</mn> <mo
class="MathClass-rel">≤</mo> <mi
>t</mi> <mo
class="MathClass-rel">≤</mo> <mn>1</mn></math>. Basically, as
<!--l. 1305--><math
xmlns="http://www.w3.org/1998/Math/MathML"
display="inline" ><mi
>t</mi> <mo
class="MathClass-rel">→</mo> <mn>0</mn></math> we obtain the minimum
curvature solution, while as <!--l. 1306--><math
xmlns="http://www.w3.org/1998/Math/MathML"
display="inline" ><mi
>t</mi> <mo
class="MathClass-rel">→</mo><mi
>∞</mi></math>
we go towards a harmonic solution (which is linear in cross-section). The theory behind all
this is quite involved and we do not have the time to explain it all here, please see <span
class="ptmri8t-">Smith and</span>
<span
class="ptmri8t-">Wessel </span>[1990] for details. Some of the most important switches for this program are indicated in
Table <a
href="#x1-46004r3">3.3<!--tex4ht:ref: tbl:surface --></a><span class="footnote-mark"><a
href="#fn2x3" id="fn2x3-bk"><sup class="textsuperscript">2</sup></a></span><a
id="x1-46003f2"></a>.
</p>
<div class="table">
<!--l. 1313--><p class="indent" > <a
id="x1-46004r3"></a></p><hr class="float" /><div class="float"
>
<div class="tabular"> <table id="TBL-13" class="tabular"
cellspacing="0" cellpadding="0" rules="groups"
><colgroup id="TBL-13-1g"><col
id="TBL-13-1" /></colgroup><colgroup id="TBL-13-2g"><col
id="TBL-13-2" /></colgroup><tr
class="hline"><td><hr /></td><td><hr /></td></tr><tr
style="vertical-align:baseline;" id="TBL-13-1-"><td style="text-align:center; white-space:nowrap;" id="TBL-13-1-1"
class="td11"> <div class="multicolumn" style="text-align:center; white-space:nowrap;"><span
class="ptmri8t-x-x-90">Option</span></div> </td><td style="text-align:center; white-space:nowrap;" id="TBL-13-1-2"
class="td11"> <div class="multicolumn" style="text-align:center; white-space:nowrap;"><span
class="ptmri8t-x-x-90">Purpose</span></div>
</td></tr><tr
class="hline"><td><hr /></td><td><hr /></td></tr><tr
style="vertical-align:baseline;" id="TBL-13-2-"><td style="text-align:left; white-space:nowrap;" id="TBL-13-2-1"
class="td11"><span
class="pcrb8t-x-x-90">-A</span><span
class="ptmri8t-x-x-90">aspect </span></td><td style="text-align:left; white-space:nowrap;" id="TBL-13-2-2"
class="td11"><span
class="ptmr8t-x-x-90">Sets aspect ratio for anisotropic grids. </span></td>
</tr><tr
class="hline"><td><hr /></td><td><hr /></td></tr><tr
style="vertical-align:baseline;" id="TBL-13-3-"><td style="text-align:left; white-space:nowrap;" id="TBL-13-3-1"
class="td11"><span
class="pcrb8t-x-x-90">-C</span><span
class="ptmri8t-x-x-90">limit </span></td><td style="text-align:left; white-space:nowrap;" id="TBL-13-3-2"
class="td11"><span
class="ptmr8t-x-x-90">Sets convergence limit. Default is 1/1000 of data range.</span></td>
</tr><tr
class="hline"><td><hr /></td><td><hr /></td></tr><tr
style="vertical-align:baseline;" id="TBL-13-4-"><td style="text-align:left; white-space:nowrap;" id="TBL-13-4-1"
class="td11"><span
class="pcrb8t-x-x-90">-T</span><span
class="ptmri8t-x-x-90">tension</span></td><td style="text-align:left; white-space:nowrap;" id="TBL-13-4-2"
class="td11"><span
class="ptmr8t-x-x-90">Sets the tension [Default is 0] </span></td>
</tr><tr
class="hline"><td><hr /></td><td><hr /></td></tr><tr
style="vertical-align:baseline;" id="TBL-13-5-"><td style="text-align:left; white-space:nowrap;" id="TBL-13-5-1"
class="td11"> </td></tr></table></div>
<br /><div class="caption"
><span class="id">Table 3.3: </span><span
class="content">Some of the options in <a
href="../html/man/surface.html" ><span
class="phvb8t-">surface</span></a><a
id="dx1-46005"></a>.</span></div><!--tex4ht:label?: x1-46004r3 -->
</div><hr class="endfloat" />
</div>
<h4 class="subsectionHead"><span class="titlemark">3.2.3 </span> <a
id="x1-470003.2.3"></a>Preprocessing</h4>
<!--l. 1328--><p class="noindent" >The <a
href="../html/man/surface.html" ><span
class="phvb8t-">surface</span></a><a
id="dx1-47001"></a> program assumes that the data have been preprocessed to eliminate aliasing, hence we must ensure
that this step is completed prior to gridding. <a
href="http://gmt.soest.hawaii.edu" ><span
class="ptmb8t-">GMT</span></a> comes with three preprocessors, called <a
href="../html/man/blockmean.html" ><span
class="phvb8t-">blockmean</span></a><a
id="dx1-47002"></a>,
<a
href="../html/man/blockmedian.html" ><span
class="phvb8t-">blockmedian</span></a><a
id="dx1-47003"></a>, and <a
href="../html/man/blockmode.html" ><span
class="phvb8t-">blockmode</span></a><a
id="dx1-47004"></a>. The first averages values inside the grid-spacing boxes, the second returns
median values, wile the latter returns modal values. As a rule of thumb, we use means for most smooth data (such
as potential fields) and medians (or modes) for rough, non-Gaussian data (such as topography). In
addition to the required <span
class="pcrb8t-">-R </span>and <span
class="pcrb8t-">-I </span>switches, these preprocessors all take the same options (listed in
Table <a
href="#x1-47005r4">3.4<!--tex4ht:ref: tbl:preprocess --></a>).
</p>
<div class="table">
<!--l. 1340--><p class="indent" > <a
id="x1-47005r4"></a></p><hr class="float" /><div class="float"
>
<div class="tabular"> <table id="TBL-14" class="tabular"
cellspacing="0" cellpadding="0" rules="groups"
><colgroup id="TBL-14-1g"><col
id="TBL-14-1" /></colgroup><colgroup id="TBL-14-2g"><col
id="TBL-14-2" /></colgroup><tr
class="hline"><td><hr /></td><td><hr /></td></tr><tr
style="vertical-align:baseline;" id="TBL-14-1-"><td style="text-align:center; white-space:nowrap;" id="TBL-14-1-1"
class="td11"> <div class="multicolumn" style="text-align:center; white-space:nowrap;"><span
class="ptmri8t-x-x-90">Option</span></div> </td><td style="text-align:center; white-space:nowrap;" id="TBL-14-1-2"
class="td11"> <div class="multicolumn" style="text-align:center; white-space:nowrap;"><span
class="ptmri8t-x-x-90">Purpose</span></div>
</td></tr><tr
class="hline"><td><hr /></td><td><hr /></td></tr><tr
style="vertical-align:baseline;" id="TBL-14-2-"><td style="text-align:left; white-space:nowrap;" id="TBL-14-2-1"
class="td11"><span
class="pcrb8t-x-x-90">-N </span></td><td style="text-align:left; white-space:nowrap;" id="TBL-14-2-2"
class="td11"><span
class="ptmr8t-x-x-90">Choose pixel node registration [Default is gridline] </span></td>
</tr><tr
class="hline"><td><hr /></td><td><hr /></td></tr><tr
style="vertical-align:baseline;" id="TBL-14-3-"><td style="text-align:left; white-space:nowrap;" id="TBL-14-3-1"
class="td11"><span
class="pcrb8t-x-x-90">-W</span><span
class="ptmr8t-x-x-90">[</span><span
class="ptmb8t-x-x-90">i</span><!--l. 1346--><math
xmlns="http://www.w3.org/1998/Math/MathML"
display="inline" ><mo
class="MathClass-rel">|</mo></math><span
class="ptmb8t-x-x-90">o</span><span
class="ptmr8t-x-x-90">]</span></td><td style="text-align:left; white-space:nowrap;" id="TBL-14-3-2"
class="td11"><span
class="ptmr8t-x-x-90">Append </span><span
class="ptmb8t-x-x-90">i </span><span
class="ptmr8t-x-x-90">or </span><span
class="ptmb8t-x-x-90">o </span><span
class="ptmr8t-x-x-90">to read or write weights in the 4th column</span></td>
</tr><tr
class="hline"><td><hr /></td><td><hr /></td></tr><tr
style="vertical-align:baseline;" id="TBL-14-4-"><td style="text-align:left; white-space:nowrap;" id="TBL-14-4-1"
class="td11"> </td></tr></table>
</div>
<br /><div class="caption"
><span class="id">Table 3.4: </span><span
class="content">Some of the preprocessing options.</span></div><!--tex4ht:label?: x1-47005r4 -->
</div><hr class="endfloat" />
</div>
<!--l. 1352--><p class="indent" > With respect to our ship data we preprocess it using the median method:
</p>
<div class="verbatim" id="verbatim-27">
blockmedian -R245/255/20/30 -I5m -V ship.xyz > ship_5m.xyz
</div>
<!--l. 1356--><p class="nopar" >
</p><!--l. 1359--><p class="indent" > The output data can now be used with surface:
</p>
<div class="verbatim" id="verbatim-28">
surface ship_5m.xyz -R245/255/20/30 -I5m -Gship.nc -V
</div>
<!--l. 1363--><p class="nopar" >
</p><!--l. 1366--><p class="indent" > If you rerun <a
href="../html/man/grdcontour.html" ><span
class="phvb8t-">grdcontour</span></a><a
id="dx1-47006"></a> on the new grid file (try it!) you will notice a big difference compared to
the grid made by <a
href="../html/man/nearneighbor.html" ><span
class="phvb8t-">nearneighbor</span></a><a
id="dx1-47007"></a>: since <a
href="../html/man/surface.html" ><span
class="phvb8t-">surface</span></a><a
id="dx1-47008"></a> is a global method it will evaluate the solution at
all nodes, even if there are no data constraints. There are numerous options available to us at this
point:
</p><ol class="enumerate1" >
<li
class="enumerate" id="x1-47010x1">We can reset all nodes too far from a data constraint to the NaN value.
</li>
<li
class="enumerate" id="x1-47012x2">We can pour white paint over those regions where contours are unreliable.
</li>
<li
class="enumerate" id="x1-47014x3">We can plot the landmass which will cover most (but not all) of the unconstrained areas.
</li>
<li
class="enumerate" id="x1-47016x4">We can set up a clip path so that only the contours in the constrained region will show.
</li></ol>
<!--l. 1389--><p class="indent" > Here we have only time to explore the latter approach. The <a
href="../html/man/psmask.html" ><span
class="phvb8t-">psmask</span></a><a
id="dx1-47017"></a> program can read the same preprocessed
data and set up a contour mask based on the data distribution. Once the clip path is activated we can
contour the final grid; we finally deactivate the clipping with a second call to <a
href="../html/man/psmask.html" ><span
class="phvb8t-">psmask</span></a><a
id="dx1-47018"></a>. Here’s the
recipe:
</p>
<div class="verbatim" id="verbatim-29">
psmask -R245/255/20/30 -I5m ship_5m.xyz -JM6i -B2 -P -K -V > map.ps
 <br />grdcontour ship.nc -J -O -K -C250 -A1000 >> map.ps
 <br />psmask -C -O >> map.ps
</div>
<!--l. 1399--><p class="nopar" >
</p>
<h3 class="sectionHead"><span class="titlemark">3.3 </span> <a
id="x1-480003.3"></a>Exercises</h3>
<a
id="dx1-48001"></a>
<!--l. 1405--><p class="noindent" >
</p><ol class="enumerate1" >
<li
class="enumerate" id="x1-48003x1">Add the continents using any color you want.
</li>
<li
class="enumerate" id="x1-48005x2">Color the clip path light gray (use <span
class="pcrb8t-">-G </span>in the first <a
href="../html/man/psmask.html" ><span
class="phvb8t-">psmask</span></a><a
id="dx1-48006"></a> call).
</li></ol>
<a
id="dx1-48007"></a>
<h2 class="chapterHead"><span class="titlemark">Chapter 4</span><br /><a
id="x1-490004"></a>SESSION FOUR</h2>
<!--l. 1418--><p class="noindent" >In our final session we will concentrate on color images and perspective views of gridded data sets. Before we start
that discussion we need to cover three important aspects of plotting that must be understood. These
are
</p><ol class="enumerate1" >
<li
class="enumerate" id="x1-49002x1">Color tables and pseudo-colors in <a
href="http://gmt.soest.hawaii.edu" ><span
class="ptmb8t-">GMT</span></a>.
</li>
<li
class="enumerate" id="x1-49004x2">Artificial illumination and how it affects colors.
</li>
<li
class="enumerate" id="x1-49006x3">Multi-dimensional grids.</li></ol>
<h3 class="sectionHead"><span class="titlemark">4.1 </span> <a
id="x1-500004.1"></a>Cpt files</h3>
<a
id="dx1-50001"></a>
<!--l. 1432--><p class="noindent" >The cpt file is discussed in detail in the <a
href="http://gmt.soest.hawaii.edu" ><span
class="ptmb8t-">GMT</span></a> Technical Reference and Cookbook, Chapter 4. Please review the
format before experimenting further.
</p><!--l. 1437--><p class="indent" > Cpt files can be created in any number of ways. <a
href="http://gmt.soest.hawaii.edu" ><span
class="ptmb8t-">GMT</span></a> provides two mechanisms: 
</p><!--l. 1440--><p class="indent" >
</p><ol class="enumerate1" >
<li
class="enumerate" id="x1-50003x1">Create simple, linear color tables given a master color table (several are built-in) and the desired
<!--l. 1443--><math
xmlns="http://www.w3.org/1998/Math/MathML"
display="inline" ><mi
>z</mi></math>-values
at color boundaries (<a
href="../html/man/makecpt.html" ><span
class="phvb8t-">makecpt</span></a><a
id="dx1-50004"></a>)
</li>
<li
class="enumerate" id="x1-50006x2">Create color tables based on a master cpt color table and the histogram-equalized distribution of
<!--l. 1447--><math
xmlns="http://www.w3.org/1998/Math/MathML"
display="inline" ><mi
>z</mi></math>-values
in a gridded data file (<a
href="../html/man/grd2cpt.html" ><span
class="phvb8t-">grd2cpt</span></a><a
id="dx1-50007"></a>)
</li></ol>
<!--l. 1451--><p class="noindent" >One can also make these files manually or with <span
class="ptmbo8t-">awk</span><a
id="dx1-50008"></a> or other tools. Here we will limit our discussion to <a
href="../html/man/makecpt.html" ><span
class="phvb8t-">makecpt</span></a><a
id="dx1-50009"></a>. Its main
argument is the name of the master color table (a list is shown if you run the program with no arguments) and the equidistant
<!--l. 1456--><math
xmlns="http://www.w3.org/1998/Math/MathML"
display="inline" ><mi
>z</mi></math>-values
to go with it. The main options are given below.
</p>
<div class="table">
<!--l. 1458--><p class="indent" > <a
id="x1-50010r1"></a></p><hr class="float" /><div class="float"
>
<div class="tabular"> <table id="TBL-15" class="tabular"
cellspacing="0" cellpadding="0" rules="groups"
><colgroup id="TBL-15-1g"><col
id="TBL-15-1" /></colgroup><colgroup id="TBL-15-2g"><col
id="TBL-15-2" /></colgroup><tr
class="hline"><td><hr /></td><td><hr /></td></tr><tr
style="vertical-align:baseline;" id="TBL-15-1-"><td style="text-align:center; white-space:nowrap;" id="TBL-15-1-1"
class="td11"><div class="multicolumn" style="text-align:center; white-space:nowrap;"><span
class="ptmri8t-x-x-90">Option</span></div></td><td style="text-align:center; white-space:nowrap;" id="TBL-15-1-2"
class="td11"> <div class="multicolumn" style="text-align:center; white-space:nowrap;"><span
class="ptmri8t-x-x-90">Purpose</span></div>
</td></tr><tr
class="hline"><td><hr /></td><td><hr /></td></tr><tr
style="vertical-align:baseline;" id="TBL-15-2-"><td style="text-align:left; white-space:nowrap;" id="TBL-15-2-1"
class="td11"><span
class="pcrb8t-x-x-90">-C </span></td><td style="text-align:left; white-space:nowrap;" id="TBL-15-2-2"
class="td11"><span
class="ptmr8t-x-x-90">Set the name of the master cpt file to use </span></td>
</tr><tr
class="hline"><td><hr /></td><td><hr /></td></tr><tr
style="vertical-align:baseline;" id="TBL-15-3-"><td style="text-align:left; white-space:nowrap;" id="TBL-15-3-1"
class="td11"><span
class="pcrb8t-x-x-90">-I </span></td><td style="text-align:left; white-space:nowrap;" id="TBL-15-3-2"
class="td11"><span
class="ptmr8t-x-x-90">Reverse the sense of the color progression </span></td>
</tr><tr
class="hline"><td><hr /></td><td><hr /></td></tr><tr
style="vertical-align:baseline;" id="TBL-15-4-"><td style="text-align:left; white-space:nowrap;" id="TBL-15-4-1"
class="td11"><span
class="pcrb8t-x-x-90">-V </span></td><td style="text-align:left; white-space:nowrap;" id="TBL-15-4-2"
class="td11"><span
class="ptmr8t-x-x-90">Run in verbose mode </span></td>
</tr><tr
class="hline"><td><hr /></td><td><hr /></td></tr><tr
style="vertical-align:baseline;" id="TBL-15-5-"><td style="text-align:left; white-space:nowrap;" id="TBL-15-5-1"
class="td11"><span
class="pcrb8t-x-x-90">-Z </span></td><td style="text-align:left; white-space:nowrap;" id="TBL-15-5-2"
class="td11"><span
class="ptmr8t-x-x-90">Make a continuous rather than discrete table</span></td>
</tr><tr
class="hline"><td><hr /></td><td><hr /></td></tr><tr
style="vertical-align:baseline;" id="TBL-15-6-"><td style="text-align:left; white-space:nowrap;" id="TBL-15-6-1"
class="td11"> </td></tr></table></div>
<br /><div class="caption"
><span class="id">Table 4.1: </span><span
class="content">Prime options available in <a
href="../html/man/makecpt.html" ><span
class="phvb8t-">makecpt</span></a><a
id="dx1-50011"></a>.</span></div><!--tex4ht:label?: x1-50010r1 -->
</div><hr class="endfloat" />
</div>
<!--l. 1472--><p class="indent" > To make discrete and continuous color cpt files for data that ranges from -20 to 60, with color changes at every
10, try these two variants:
</p>
<div class="verbatim" id="verbatim-30">
makecpt -Crainbow -T-20/60/10 > disc.cpt
 <br />makecpt -Crainbow -T-20/60/10 -Z > cont.cpt
</div>
<!--l. 1478--><p class="nopar" >
</p><!--l. 1481--><p class="noindent" >We can plot these color tables with <a
href="../html/man/psscale.html" ><span
class="phvb8t-">psscale</span></a><a
id="dx1-50012"></a>; the options worth mentioning here are listed in Table <a
href="#x1-50013r2">4.2<!--tex4ht:ref: tbl:psscale --></a>. In
addition, the <span
class="pcrb8t-">-B </span>option can be used to set the title and unit label (and optionally to set the annotation-, tick-, and
grid-line intervals for the colorbars.)
</p>
<div class="table">
<!--l. 1488--><p class="indent" > <a
id="x1-50013r2"></a></p><hr class="float" /><div class="float"
>
<div class="tabular"> <table id="TBL-16" class="tabular"
cellspacing="0" cellpadding="0" rules="groups"
><colgroup id="TBL-16-1g"><col
id="TBL-16-1" /></colgroup><colgroup id="TBL-16-2g"><col
id="TBL-16-2" /></colgroup><tr
class="hline"><td><hr /></td><td><hr /></td></tr><tr
style="vertical-align:baseline;" id="TBL-16-1-"><td style="text-align:center; white-space:nowrap;" id="TBL-16-1-1"
class="td11"> <div class="multicolumn" style="text-align:center; white-space:nowrap;"><span
class="ptmri8t-x-x-90">Option</span></div> </td><td style="text-align:center; white-space:nowrap;" id="TBL-16-1-2"
class="td11"> <div class="multicolumn" style="text-align:center; white-space:nowrap;"><span
class="ptmri8t-x-x-90">Purpose</span></div>
</td></tr><tr
class="hline"><td><hr /></td><td><hr /></td></tr><tr
style="vertical-align:baseline;" id="TBL-16-2-"><td style="text-align:left; white-space:nowrap;" id="TBL-16-2-1"
class="td11"><span
class="pcrb8t-x-x-90">-C</span><span
class="ptmri8t-x-x-90">cptfile </span></td><td style="text-align:left; white-space:nowrap;" id="TBL-16-2-2"
class="td11"><span
class="ptmr8t-x-x-90">The required cpt file </span></td>
</tr><tr
class="hline"><td><hr /></td><td><hr /></td></tr><tr
style="vertical-align:baseline;" id="TBL-16-3-"><td style="text-align:left; white-space:nowrap;" id="TBL-16-3-1"
class="td11"><span
class="pcrb8t-x-x-90">-D</span><span
class="ptmri8t-x-x-90">xpos</span><span
class="ptmr8t-x-x-90">/</span><span
class="ptmri8t-x-x-90">ypos</span><span
class="ptmr8t-x-x-90">/</span><span
class="ptmri8t-x-x-90">length</span><span
class="ptmr8t-x-x-90">/</span><span
class="ptmri8t-x-x-90">width</span><span
class="ptmr8t-x-x-90">[</span><span
class="ptmb8t-x-x-90">h</span><span
class="ptmr8t-x-x-90">]</span></td><td style="text-align:left; white-space:nowrap;" id="TBL-16-3-2"
class="td11"><span
class="ptmr8t-x-x-90">Sets the position of the center/left and dimensions of scale bar.</span></td>
</tr><tr
class="hline"><td><hr /></td><td><hr /></td></tr><tr
style="vertical-align:baseline;" id="TBL-16-4-"><td style="text-align:left; white-space:nowrap;" id="TBL-16-4-1"
class="td11"> </td><td style="text-align:left; white-space:nowrap;" id="TBL-16-4-2"
class="td11"><span
class="ptmr8t-x-x-90">Append </span><span
class="ptmb8t-x-x-90">h </span><span
class="ptmr8t-x-x-90">to get horizontal bar and give center/top instead </span></td>
</tr><tr
class="hline"><td><hr /></td><td><hr /></td></tr><tr
style="vertical-align:baseline;" id="TBL-16-5-"><td style="text-align:left; white-space:nowrap;" id="TBL-16-5-1"
class="td11"><span
class="pcrb8t-x-x-90">-I</span><span
class="ptmri8t-x-x-90">max_intensity </span></td><td style="text-align:left; white-space:nowrap;" id="TBL-16-5-2"
class="td11"><span
class="ptmr8t-x-x-90">Add illumination effects </span></td>
</tr><tr
class="hline"><td><hr /></td><td><hr /></td></tr><tr
style="vertical-align:baseline;" id="TBL-16-6-"><td style="text-align:left; white-space:nowrap;" id="TBL-16-6-1"
class="td11"> </td></tr></table></div>
<br /><div class="caption"
><span class="id">Table 4.2: </span><span
class="content">The main switches and options in <a
href="../html/man/psscale.html" ><span
class="phvb8t-">psscale</span></a><a
id="dx1-50014"></a>.</span></div><!--tex4ht:label?: x1-50013r2 -->
</div><hr class="endfloat" />
</div>
<div class="verbatim" id="verbatim-31">
psbasemap -R0/8.5/0/11 -Jx1i -P -B0 -K > bar.ps
 <br />psscale -D3i/3i/4i/0.5ih -Cdisc.cpt -B:discrete: -O -K >> bar.ps
 <br />psscale -D3i/5i/4i/0.5ih -Ccont.cpt -B:continuous: -O -K >> bar.ps
 <br />psscale -D3i/7i/4i/0.5ih -Cdisc.cpt -B:discrete: -I0.5 -O -K >> bar.ps
 <br />psscale -D3i/9i/4i/0.5ih -Ccont.cpt -B:continuous: -I0.5 -O >> bar.ps
</div>
<!--l. 1508--><p class="nopar" >
</p>
<h4 class="subsectionHead"><span class="titlemark">4.1.1 </span> <a
id="x1-510004.1.1"></a>Exercises</h4>
<a
id="dx1-51001"></a>
<!--l. 1514--><p class="noindent" >
</p><ol class="enumerate1" >
<li
class="enumerate" id="x1-51003x1">Redo the <a
href="../html/man/makecpt.html" ><span
class="phvb8t-">makecpt</span></a><a
id="dx1-51004"></a> exercise using the master table <span
class="ptmri8t-">hot </span>and redo the bar plot.
</li>
<li
class="enumerate" id="x1-51006x2">Try specifying <span
class="pcrb8t-">-B</span>10g5.
</li></ol>
<a
id="dx1-51007"></a>
<!--l. 1524--><p class="noindent" >
</p>
<h3 class="sectionHead"><span class="titlemark">4.2 </span> <a
id="x1-520004.2"></a>Illumination and intensities</h3>
<!--l. 1526--><p class="noindent" ><a
href="http://gmt.soest.hawaii.edu" ><span
class="ptmb8t-">GMT</span></a> allows for artificial illumination and shading. What this means is that we imagine an artificial sun placed at
infinity in some azimuth and elevation position illuminating our surface. The parts of the surface that slope toward
the sun should brighten while those sides facing away should become darker; no shadows are cast as a result of
topographic undulations.
</p><!--l. 1533--><p class="indent" > While it is clear that the actual slopes of the surface and the orientation of the sun enter into these calculations,
there is clearly an arbitrary element when the surface is not topographic relief but some other quantity. For
instance, what does the slope toward the sun mean if we are plotting a grid of heat flow anomalies? While there are
many ways to accomplish what we want, <a
href="http://gmt.soest.hawaii.edu" ><span
class="ptmb8t-">GMT</span></a> offers a relatively simple way: We may calculate the gradient of
the surface in the direction of the sun and normalize these values to fall in the <span
class="ptmr8c-">±</span>1 range; +1 means maximum sun
exposure and -1 means complete shade. Although we will not show it here, it should be added that <a
href="http://gmt.soest.hawaii.edu" ><span
class="ptmb8t-">GMT</span></a> treats the
intensities as a separate data set. Thus, while these values are often derived from the relief surface
we want to image they could be separately observed quantities such as back-scatter information. <a
id="dx1-52001"></a><a
id="dx1-52002"></a>
<a
id="dx1-52003"></a>
</p><!--l. 1551--><p class="indent" > Colors in <a
href="http://gmt.soest.hawaii.edu" ><span
class="ptmb8t-">GMT</span></a> are specified in the RGB system used for computer screens; it mixes red, green, and blue light
to achieve other colors. The RGB system is a Cartesian coordinate system and produces a color cube. For
reasons better explained in Appendix I in the Reference book it is difficult to darken and brighten
a color based on its RGB values and an alternative coordinate system is used instead; here we use
the HSV system. If you hold the color cube so that the black and white corners are along a vertical
axis, then the other 6 corners project onto the horizontal plane to form a hexagon; the corners of this
hexagon are the primary colors Red, Yellow, Green, Cyan, Blue, and Magenta. The CMY colors are
the complimentary colors and are used when paints are mixed to produce a new color (this is how
printers operate; they also add pure black (K) to avoid making gray from CMY). In this coordinate
system the angle 0–360<span
class="ptmr8c-">°</span> is the hue (H); the Saturation and Value are harder to explain. Suffice it to
say here that we intend to darken any pure color (on the cube facets) by keeping H fixed and adding
black and brighten it by adding white; for interior points in the cube we will add or remove gray.
This operation is efficiently done in the HSV coordinate system; hence all <a
href="http://gmt.soest.hawaii.edu" ><span
class="ptmb8t-">GMT</span></a> shading operations
involve translating from RGB to HSV, do the illumination effect, and transform back the modified RGB
values.
</p><!--l. 1572--><p class="noindent" >
</p>
<h3 class="sectionHead"><span class="titlemark">4.3 </span> <a
id="x1-530004.3"></a>Color images</h3>
<a
id="dx1-53001"></a>
<!--l. 1575--><p class="noindent" >Once a cpt file has been made it is relatively straightforward to generate a color image of a gridded data. Here, we
will extract a subset of the global 30" DEM (data id 9) from USGS:
</p>
<div class="verbatim" id="verbatim-32">
grdraster 9 -R-108/-103/35/40 -Gus.nc
</div>
<!--l. 1581--><p class="nopar" >
</p><!--l. 1584--><p class="indent" > You can find the grid <span class="underline">us.nc</span> also in the <span class="underline">tutorial</span> directory of your <a
href="http://gmt.soest.hawaii.edu" ><span
class="ptmb8t-">GMT</span></a> installation. Using <a
href="../html/man/grdinfo.html" ><span
class="phvb8t-">grdinfo</span></a><a
id="dx1-53002"></a> we find that the data
ranges from <!--l. 1586--><math
xmlns="http://www.w3.org/1998/Math/MathML"
display="inline" > <mo
class="MathClass-rel">~</mo></math>1000m
to <!--l. 1588--><math
xmlns="http://www.w3.org/1998/Math/MathML"
display="inline" > <mo
class="MathClass-rel">~</mo></math>4300m so
we make a cpt file accordingly:
</p>
<div class="verbatim" id="verbatim-33">
makecpt -Crainbow -T1000/5000/500 -Z > topo.cpt
</div>
<!--l. 1592--><p class="nopar" >
</p><!--l. 1595--><p class="indent" > Color images are made with <a
href="../html/man/grdimage.html" ><span
class="phvb8t-">grdimage</span></a><a
id="dx1-53003"></a> which takes the usual common command options (by default the <span
class="pcrb8t-">-R </span>is
taken from the data set) and a cptfile; the main other options are
</p>
<div class="table">
<!--l. 1599--><p class="indent" > <a
id="x1-53004r3"></a></p><hr class="float" /><div class="float"
>
<div class="tabular"> <table id="TBL-17" class="tabular"
cellspacing="0" cellpadding="0" rules="groups"
><colgroup id="TBL-17-1g"><col
id="TBL-17-1" /></colgroup><colgroup id="TBL-17-2g"><col
id="TBL-17-2" /></colgroup><tr
class="hline"><td><hr /></td><td><hr /></td></tr><tr
style="vertical-align:baseline;" id="TBL-17-1-"><td style="text-align:center; white-space:nowrap;" id="TBL-17-1-1"
class="td11"> <div class="multicolumn" style="text-align:center; white-space:nowrap;"><span
class="ptmri8t-x-x-90">Option</span></div> </td><td style="text-align:center; white-space:nowrap;" id="TBL-17-1-2"
class="td11"> <div class="multicolumn" style="text-align:center; white-space:nowrap;"><span
class="ptmri8t-x-x-90">Purpose</span></div>
</td></tr><tr
class="hline"><td><hr /></td><td><hr /></td></tr><tr
style="vertical-align:baseline;" id="TBL-17-2-"><td style="text-align:left; white-space:nowrap;" id="TBL-17-2-1"
class="td11"><span
class="pcrb8t-x-x-90">-E</span><span
class="ptmri8t-x-x-90">dpi </span></td><td style="text-align:left; white-space:nowrap;" id="TBL-17-2-2"
class="td11"><span
class="ptmr8t-x-x-90">Sets the desired resolution of the image [Default is data resolution]</span></td>
</tr><tr
class="hline"><td><hr /></td><td><hr /></td></tr><tr
style="vertical-align:baseline;" id="TBL-17-3-"><td style="text-align:left; white-space:nowrap;" id="TBL-17-3-1"
class="td11"><span
class="pcrb8t-x-x-90">-I</span><span
class="ptmri8t-x-x-90">intenfile</span></td><td style="text-align:left; white-space:nowrap;" id="TBL-17-3-2"
class="td11"><span
class="ptmr8t-x-x-90">Use artificial illumination using intensities from </span><span
class="ptmri8t-x-x-90">intensfile </span></td>
</tr><tr
class="hline"><td><hr /></td><td><hr /></td></tr><tr
style="vertical-align:baseline;" id="TBL-17-4-"><td style="text-align:left; white-space:nowrap;" id="TBL-17-4-1"
class="td11"><span
class="pcrb8t-x-x-90">-M </span></td><td style="text-align:left; white-space:nowrap;" id="TBL-17-4-2"
class="td11"><span
class="ptmr8t-x-x-90">Force gray shade using the (television) YIQ conversion </span></td>
</tr><tr
class="hline"><td><hr /></td><td><hr /></td></tr><tr
style="vertical-align:baseline;" id="TBL-17-5-"><td style="text-align:left; white-space:nowrap;" id="TBL-17-5-1"
class="td11"> </td></tr></table></div>
<br /><div class="caption"
><span class="id">Table 4.3: </span><span
class="content">The main options in <a
href="../html/man/grdimage.html" ><span
class="phvb8t-">grdimage</span></a><a
id="dx1-53005"></a>.</span></div><!--tex4ht:label?: x1-53004r3 -->
</div><hr class="endfloat" />
</div>
<!--l. 1612--><p class="indent" > We want to make a plain color map with a color bar superimposed above the plot. We try
</p>
<div class="verbatim" id="verbatim-34">
grdimage us.nc -JM6i -P -B2 -Ctopo.cpt -V -K > topo.ps
 <br />psscale -D3i/8.5i/5i/0.25ih -Ctopo.cpt -I0.4 -B/:m: -O >> topo.ps
</div>
<!--l. 1618--><p class="nopar" >
</p><!--l. 1621--><p class="indent" > The plain color map lacks detail and fails to reveal the topographic complexity of this Rocky Mountain
region. What it needs is artificial illumination. We want to simulate shading by a sun source in the east,
hence we derive the required intensities from the gradients of the topography in the N90<span
class="ptmr8c-">°</span>E direction
using <a
href="../html/man/grdgradient.html" ><span
class="phvb8t-">grdgradient</span></a><a
id="dx1-53006"></a>. Other than the required input and output filenames, the available options are
<a
id="dx1-53007"></a><a
id="dx1-53008"></a>
</p>
<div class="table">
<!--l. 1630--><p class="indent" > <a
id="x1-53009r4"></a></p><hr class="float" /><div class="float"
>
<div class="tabular"> <table id="TBL-18" class="tabular"
cellspacing="0" cellpadding="0" rules="groups"
><colgroup id="TBL-18-1g"><col
id="TBL-18-1" /></colgroup><colgroup id="TBL-18-2g"><col
id="TBL-18-2" /></colgroup><tr
class="hline"><td><hr /></td><td><hr /></td></tr><tr
style="vertical-align:baseline;" id="TBL-18-1-"><td style="text-align:center; white-space:nowrap;" id="TBL-18-1-1"
class="td11"> <div class="multicolumn" style="text-align:center; white-space:nowrap;"><span
class="ptmri8t-x-x-90">Option</span></div> </td><td style="text-align:center; white-space:nowrap;" id="TBL-18-1-2"
class="td11"> <div class="multicolumn" style="text-align:center; white-space:nowrap;"><span
class="ptmri8t-x-x-90">Purpose</span></div>
</td></tr><tr
class="hline"><td><hr /></td><td><hr /></td></tr><tr
style="vertical-align:baseline;" id="TBL-18-2-"><td style="text-align:left; white-space:nowrap;" id="TBL-18-2-1"
class="td11"><span
class="pcrb8t-x-x-90">-A</span><span
class="ptmri8t-x-x-90">azimuth </span></td><td style="text-align:left; white-space:nowrap;" id="TBL-18-2-2"
class="td11"><span
class="ptmr8t-x-x-90">Azimuthal direction for gradients </span></td>
</tr><tr
class="hline"><td><hr /></td><td><hr /></td></tr><tr
style="vertical-align:baseline;" id="TBL-18-3-"><td style="text-align:left; white-space:nowrap;" id="TBL-18-3-1"
class="td11"><span
class="pcrb8t-x-x-90">-M </span></td><td style="text-align:left; white-space:nowrap;" id="TBL-18-3-2"
class="td11"><span
class="ptmr8t-x-x-90">Indicates that this is a geographic grid </span></td>
</tr><tr
class="hline"><td><hr /></td><td><hr /></td></tr><tr
style="vertical-align:baseline;" id="TBL-18-4-"><td style="text-align:left; white-space:nowrap;" id="TBL-18-4-1"
class="td11"><span
class="pcrb8t-x-x-90">-N</span><span
class="ptmr8t-x-x-90">[</span><span
class="ptmb8t-x-x-90">t</span><!--l. 1637--><math
xmlns="http://www.w3.org/1998/Math/MathML"
display="inline" ><mo
class="MathClass-rel">|</mo></math><span
class="ptmb8t-x-x-90">e</span><span
class="ptmr8t-x-x-90">][</span><span
class="ptmri8t-x-x-90">norm</span><span
class="ptmr8t-x-x-90">[/</span><span
class="ptmri8t-x-x-90">offset</span><span
class="ptmr8t-x-x-90">]]</span></td><td style="text-align:left; white-space:nowrap;" id="TBL-18-4-2"
class="td11"><span
class="ptmr8t-x-x-90">Normalize gradients by </span><span
class="ptmri8t-x-x-90">norm/offset </span><span
class="ptmr8t-x-x-90">[= 1/0 by default]. </span></td>
</tr><tr
style="vertical-align:baseline;" id="TBL-18-5-"><td style="text-align:left; white-space:nowrap;" id="TBL-18-5-1"
class="td11"> </td><td style="text-align:left; white-space:nowrap;" id="TBL-18-5-2"
class="td11"><span
class="ptmr8t-x-x-90">Insert </span><span
class="ptmb8t-x-x-90">t </span><span
class="ptmr8t-x-x-90">to normalize by the </span><!--l. 1638--><math
xmlns="http://www.w3.org/1998/Math/MathML"
display="inline" ><mi
>t</mi><mi
>a</mi><msup><mrow
><mi
>n</mi></mrow><mrow
><mo
class="MathClass-bin">-</mo><mn>1</mn></mrow></msup
></math> <span
class="ptmr8t-x-x-90">transformation.</span></td>
</tr><tr
style="vertical-align:baseline;" id="TBL-18-6-"><td style="text-align:left; white-space:nowrap;" id="TBL-18-6-1"
class="td11"> </td><td style="text-align:left; white-space:nowrap;" id="TBL-18-6-2"
class="td11"><span
class="ptmr8t-x-x-90">Insert </span><span
class="ptmb8t-x-x-90">e </span><span
class="ptmr8t-x-x-90">to normalize by the cumulative Laplace distribution. </span></td>
</tr><tr
class="hline"><td><hr /></td><td><hr /></td></tr><tr
style="vertical-align:baseline;" id="TBL-18-7-"><td style="text-align:left; white-space:nowrap;" id="TBL-18-7-1"
class="td11"> </td></tr></table>
</div>
<br /><div class="caption"
><span class="id">Table 4.4: </span><span
class="content">The <a
href="../html/man/grdgradient.html" ><span
class="phvb8t-">grdgradient</span></a><a
id="dx1-53010"></a> options.</span></div><!--tex4ht:label?: x1-53009r4 -->
</div><hr class="endfloat" />
</div>
<!--l. 1645--><p class="indent" > Figure <a
href="#x1-53011r1">4.1<!--tex4ht:ref: fig:GMT_atan --></a> shows that raw slopes from bathymetry tend to be far from normally distributed (left).
By using the inverse tangent transformation we can ensure a more uniform distribution (right). The
inverse tangent transform simply takes the raw slope estimate (the <span
class="ptmri8t-">x </span>value at the arrow) and returns the
corresponding inverse tangent value (normalized to fall in the <span
class="ptmr8c-">±</span>1 range; horizontal arrow pointing to the
<span
class="ptmri8t-">y</span>-value).
</p>
<hr class="figure" /><div class="figure"
>
<a
id="x1-53011r1"></a>
<!--l. 1653--><p class="noindent" ><img
src="images/GMT_atan.png" alt="PIC"
/>
<br /> </p><div class="caption"
><span class="id">Figure 4.1: </span><span
class="content">How the inverse tangent operation works.</span></div><!--tex4ht:label?: x1-53011r1 -->
</div><hr class="endfigure" />
<!--l. 1655--><p class="indent" > Both <span
class="pcrb8t-">-Ne </span>and <span
class="pcrb8t-">-Nt </span>yield well behaved gradients. Personally, we prefer to use the <span
class="pcrb8t-">-Ne </span>option; the
value of <span
class="ptmri8t-">norm </span>is subjective and you may experiment somewhat in the 0.5–5 range. For our case we
choose
</p>
<div class="verbatim" id="verbatim-35">
grdgradient us.nc -Ne0.8 -A100 -M -Gus_i.nc
</div>
<!--l. 1662--><p class="nopar" >
</p><!--l. 1665--><p class="indent" > Given the cpt file and the two gridded data sets we can create the shaded relief image:
</p>
<div class="verbatim" id="verbatim-36">
grdimage us.nc -Ius_i.nc -JM6i -P -B2 -Ctopo.cpt -K > topo.ps
 <br />psscale -D3i/8.5i/5i/0.25ih -Ctopo.cpt -I0.4 -B/:m: -O >> topo.ps
</div>
<!--l. 1671--><p class="nopar" >
</p>
<h4 class="subsectionHead"><span class="titlemark">4.3.1 </span> <a
id="x1-540004.3.1"></a>Exercises</h4>
<a
id="dx1-54001"></a>
<!--l. 1677--><p class="noindent" >
</p><ol class="enumerate1" >
<li
class="enumerate" id="x1-54003x1">Force a gray-shade image.
</li>
<li
class="enumerate" id="x1-54005x2">Rerun <a
href="../html/man/grdgradient.html" ><span
class="phvb8t-">grdgradient</span></a><a
id="dx1-54006"></a> with <span
class="pcrb8t-">-N</span>1.
</li></ol>
<a
id="dx1-54007"></a>
<!--l. 1686--><p class="noindent" >
</p>
<h3 class="sectionHead"><span class="titlemark">4.4 </span> <a
id="x1-550004.4"></a>Multi-dimensional maps</h3>
<a
id="dx1-55001"></a>
<!--l. 1689--><p class="noindent" >Climate data, like ocean temperatures or atmospheric pressure, are often provided as multi-dimensional (3-D, 4-D
or 5-D) grids in netCDF format. This section will demonstrate that <a
href="http://gmt.soest.hawaii.edu" ><span
class="ptmb8t-">GMT</span></a> is able to plot “horizonal” slices
(spanning latitude and longitude) of such grids without much effort.
</p><!--l. 1694--><p class="indent" > As an example we will download the Seasonal Analysed Mean Temperature from the <a
href="http://www.cdc.noaa.gov/cdc/data.nodc.woa98.html" >World Ocean Atlas 1998</a>.
The file in question is named <a
href="ftp://ftp.cdc.noaa.gov/Datasets/nodc.woa98/temperat/seasonal/otemp.anal1deg.nc" ><span class="underline">otemp.anal1deg.nc</span></a>.
</p><!--l. 1699--><p class="indent" > You can look at the information pertained in this file using the program <span
class="ptmbo8t-">ncdump</span><a
id="dx1-55002"></a> and notice that the variable
that we want to plot (otemp) is a four-dimensional variable of time, level (i.e., depth), latitude and
longitude.
</p>
<div class="verbatim" id="verbatim-37">
ncdump -h otemp.anal1deg.nc
</div>
<!--l. 1705--><p class="nopar" >
</p><!--l. 1708--><p class="indent" > We will need to make an appropriate color scale, running from -2<span
class="ptmr8c-">°</span>C (freezing temperature of salt water) to
30<span
class="ptmr8c-">°</span>C (highest likely ocean temperature). We do this as follows:
</p>
<div class="verbatim" id="verbatim-38">
makecpt -Cno_green -T-2/30/2 > otemp.cpt
</div>
<!--l. 1713--><p class="nopar" >
</p><!--l. 1716--><p class="indent" > Let us focus on the temperatures in Summer (that is the third season, July through September) at sea level (that
is the first level). To plot these in a Mollweide projection we use:
</p>
<div class="verbatim" id="verbatim-39">
grdimage -Rg -JW180/9i ~otemp.anal1deg.nc?otemp[2,0]~ -Cotemp.cpt -Bg30 \
 <br />   > otemp.ps
</div>
<!--l. 1723--><p class="nopar" >
</p><!--l. 1726--><p class="indent" > The addition <span class="underline">?otemp[2,0]</span> indicates which variable to retrieve from the netCDF file (otemp) and that we need
the third time step and first level. The numbering of the time steps and levels starts at zero, therefore <span class="underline">[2,0]</span>. Make
sure to put the whole file name within quotes since the characters <span class="obeylines-h"><span class="verb"><span
class="pcrr8t-">?</span></span></span>, <span class="obeylines-h"><span class="verb"><span
class="pcrr8t-">[</span></span></span> and <span class="obeylines-h"><span class="verb"><span
class="pcrr8t-">]</span></span></span> have special meaning in
Unix.
</p><!--l. 1732--><p class="noindent" >
</p>
<h4 class="subsectionHead"><span class="titlemark">4.4.1 </span> <a
id="x1-560004.4.1"></a>Exercises</h4>
<a
id="dx1-56001"></a>
<!--l. 1735--><p class="noindent" >
</p><ol class="enumerate1" >
<li
class="enumerate" id="x1-56003x1">Plot the temperatures for Spring at 5000 m depth. (Hint: use <span class="underline">ncdump -v level</span> to figure out what level
number that is).
</li>
<li
class="enumerate" id="x1-56005x2">Include a color scale at the bottom of the plot.
</li></ol>
<a
id="dx1-56006"></a>
<!--l. 1745--><p class="noindent" >
</p>
<h3 class="sectionHead"><span class="titlemark">4.5 </span> <a
id="x1-570004.5"></a>Perspective views</h3>
<a
id="dx1-57001"></a>
<!--l. 1748--><p class="noindent" >Our final undertaking in this tutorial is to examine three-dimensional perspective views. <a
href="http://gmt.soest.hawaii.edu" ><span
class="ptmb8t-">GMT</span></a> is
currently limited to vantage points at infinity; thus we are unable to do fly-by’s through canyons etc. The
<a
href="http://gmt.soest.hawaii.edu" ><span
class="ptmb8t-">GMT</span></a> module that produces perspective views of gridded data files is <a
href="../html/man/grdview.html" ><span
class="phvb8t-">grdview</span></a><a
id="dx1-57002"></a>. It can make two kinds of
plots:
</p><!--l. 1754--><p class="indent" >
</p><ol class="enumerate1" >
<li
class="enumerate" id="x1-57004x1">Mesh or wire-frame plot (with or without superimposed contours)
</li>
<li
class="enumerate" id="x1-57006x2">Color-coded surface (with optional shading, contours, or draping).
</li></ol>
<!--l. 1762--><p class="indent" > Regardless of plot type, some arguments must be specified; these are
</p><!--l. 1764--><p class="indent" >
</p><ol class="enumerate1" >
<li
class="enumerate" id="x1-57008x1"><span
class="ptmri8t-">relief_file</span>; a gridded data set of the surface.
</li>
<li
class="enumerate" id="x1-57010x2"><span
class="pcrb8t-">-J </span>for the desired map projection.
</li>
<li
class="enumerate" id="x1-57012x3"><span
class="pcrb8t-">-JZ</span><span
class="ptmri8t-">height </span>for the vertical scaling.
</li>
<li
class="enumerate" id="x1-57014x4"><span
class="pcrb8t-">-E</span><span
class="ptmri8t-">azimuth</span>/<span
class="ptmri8t-">elevation </span>for vantage point.
</li></ol>
<!--l. 1777--><p class="indent" > In addition, some options may be required:
</p>
<div class="table">
<!--l. 1779--><p class="indent" > <a
id="x1-57015r5"></a></p><hr class="float" /><div class="float"
>
<div class="tabular"> <table id="TBL-19" class="tabular"
cellspacing="0" cellpadding="0" rules="groups"
><colgroup id="TBL-19-1g"><col
id="TBL-19-1" /></colgroup><colgroup id="TBL-19-2g"><col
id="TBL-19-2" /></colgroup><tr
class="hline"><td><hr /></td><td><hr /></td></tr><tr
style="vertical-align:baseline;" id="TBL-19-1-"><td style="text-align:center; white-space:nowrap;" id="TBL-19-1-1"
class="td11"> <div class="multicolumn" style="text-align:center; white-space:nowrap;"><span
class="ptmri8t-x-x-90">Option</span></div> </td><td style="text-align:center; white-space:nowrap;" id="TBL-19-1-2"
class="td11"> <div class="multicolumn" style="text-align:center; white-space:nowrap;"><span
class="ptmri8t-x-x-90">Purpose</span></div>
</td></tr><tr
class="hline"><td><hr /></td><td><hr /></td></tr><tr
style="vertical-align:baseline;" id="TBL-19-2-"><td style="text-align:left; white-space:nowrap;" id="TBL-19-2-1"
class="td11"><span
class="pcrb8t-x-x-90">-C</span><span
class="ptmri8t-x-x-90">cptfile </span></td><td style="text-align:left; white-space:nowrap;" id="TBL-19-2-2"
class="td11"><span
class="ptmr8t-x-x-90">The </span><span
class="ptmri8t-x-x-90">cptfile </span><span
class="ptmr8t-x-x-90">is required for color -coded surfaces and for contoured mesh plots </span></td>
</tr><tr
class="hline"><td><hr /></td><td><hr /></td></tr><tr
style="vertical-align:baseline;" id="TBL-19-3-"><td style="text-align:left; white-space:nowrap;" id="TBL-19-3-1"
class="td11"><span
class="pcrb8t-x-x-90">-G</span><span
class="ptmri8t-x-x-90">drape_file</span></td><td style="text-align:left; white-space:nowrap;" id="TBL-19-3-2"
class="td11"><span
class="ptmr8t-x-x-90">Assign colors using </span><span
class="ptmri8t-x-x-90">drape_file </span><span
class="ptmr8t-x-x-90">instead of </span><span
class="ptmri8t-x-x-90">relief_file </span></td>
</tr><tr
class="hline"><td><hr /></td><td><hr /></td></tr><tr
style="vertical-align:baseline;" id="TBL-19-4-"><td style="text-align:left; white-space:nowrap;" id="TBL-19-4-1"
class="td11"><span
class="pcrb8t-x-x-90">-I</span><span
class="ptmri8t-x-x-90">intens_file</span></td><td style="text-align:left; white-space:nowrap;" id="TBL-19-4-2"
class="td11"><span
class="ptmr8t-x-x-90">File with illumination intensities </span></td>
</tr><tr
class="hline"><td><hr /></td><td><hr /></td></tr><tr
style="vertical-align:baseline;" id="TBL-19-5-"><td style="text-align:left; white-space:nowrap;" id="TBL-19-5-1"
class="td11"><span
class="pcrb8t-x-x-90">-Qm </span></td><td style="text-align:left; white-space:nowrap;" id="TBL-19-5-2"
class="td11"><span
class="ptmr8t-x-x-90">Selects mesh plot </span></td>
</tr><tr
class="hline"><td><hr /></td><td><hr /></td></tr><tr
style="vertical-align:baseline;" id="TBL-19-6-"><td style="text-align:left; white-space:nowrap;" id="TBL-19-6-1"
class="td11"><span
class="pcrb8t-x-x-90">-Qs</span><span
class="ptmr8t-x-x-90">[</span><span
class="ptmb8t-x-x-90">m</span><span
class="ptmr8t-x-x-90">] </span></td><td style="text-align:left; white-space:nowrap;" id="TBL-19-6-2"
class="td11"><span
class="ptmr8t-x-x-90">Surface plot using polygons; append </span><span
class="ptmb8t-x-x-90">m </span><span
class="ptmr8t-x-x-90">to show mesh. This option allows for </span><span
class="pcrb8t-x-x-90">-W </span></td>
</tr><tr
class="hline"><td><hr /></td><td><hr /></td></tr><tr
style="vertical-align:baseline;" id="TBL-19-7-"><td style="text-align:left; white-space:nowrap;" id="TBL-19-7-1"
class="td11"><span
class="pcrb8t-x-x-90">-Qi</span><span
class="ptmri8t-x-x-90">dpi</span><span
class="ptmr8t-x-x-90">[</span><span
class="ptmb8t-x-x-90">g</span><span
class="ptmr8t-x-x-90">] </span></td><td style="text-align:left; white-space:nowrap;" id="TBL-19-7-2"
class="td11"><span
class="ptmr8t-x-x-90">Image by scan-line conversion. Specify </span><span
class="ptmri8t-x-x-90">dpi</span><span
class="ptmr8t-x-x-90">; append </span><span
class="ptmb8t-x-x-90">g </span><span
class="ptmr8t-x-x-90">to force gray-shade image. </span><span
class="pcrb8t-x-x-90">-B </span><span
class="ptmr8t-x-x-90">is disabled.</span></td>
</tr><tr
class="hline"><td><hr /></td><td><hr /></td></tr><tr
style="vertical-align:baseline;" id="TBL-19-8-"><td style="text-align:left; white-space:nowrap;" id="TBL-19-8-1"
class="td11"><span
class="pcrb8t-x-x-90">-W</span><span
class="ptmri8t-x-x-90">pen </span></td><td style="text-align:left; white-space:nowrap;" id="TBL-19-8-2"
class="td11"><span
class="ptmr8t-x-x-90">Draw contours on top of surface (except with </span><span
class="pcrb8t-x-x-90">-Qi</span><span
class="ptmr8t-x-x-90">) </span></td>
</tr><tr
class="hline"><td><hr /></td><td><hr /></td></tr><tr
style="vertical-align:baseline;" id="TBL-19-9-"><td style="text-align:left; white-space:nowrap;" id="TBL-19-9-1"
class="td11"> </td></tr></table></div>
<br /><div class="caption"
><span class="id">Table 4.5: </span><span
class="content">The most useful options in <a
href="../html/man/grdview.html" ><span
class="phvb8t-">grdview</span></a><a
id="dx1-57016"></a>.</span></div><!--tex4ht:label?: x1-57015r5 -->
</div><hr class="endfloat" />
</div>
<h4 class="subsectionHead"><span class="titlemark">4.5.1 </span> <a
id="x1-580004.5.1"></a>Mesh-plot</h4>
<a
id="dx1-58001"></a>
<!--l. 1799--><p class="noindent" >Mesh plots work best on smaller data sets. We again use the small subset of the ETOPO5 data over Bermuda and
make a quick-and-dirty cpt file:
</p>
<div class="verbatim" id="verbatim-40">
grd2cpt bermuda.nc -Cocean > bermuda.cpt
</div>
<!--l. 1805--><p class="nopar" >
</p><!--l. 1808--><p class="indent" > A simple mesh plot can therefore be obtained with
</p>
<div class="verbatim" id="verbatim-41">
grdview bermuda.nc -JM5i -P -JZ2i -E135/30 -B2 -Cbermuda.cpt > map.ps
</div>
<!--l. 1812--><p class="nopar" >
</p><!--l. 1816--><p class="noindent" >
</p>
<h5 class="subsubsectionHead"><a
id="x1-590004.5.1"></a>Exercises</h5>
<a
id="dx1-59001"></a>
<!--l. 1819--><p class="noindent" >
</p><ol class="enumerate1" >
<li
class="enumerate" id="x1-59003x1">Select another vantage point and vertical height.
</li></ol>
<a
id="dx1-59004"></a>
<!--l. 1826--><p class="noindent" >
</p>
<h4 class="subsectionHead"><span class="titlemark">4.5.2 </span> <a
id="x1-600004.5.2"></a>Color-coded view</h4>
<!--l. 1828--><p class="noindent" >We will make a perspective, color-coded view of the US Rockies from the southeast. This is done
using
</p>
<div class="verbatim" id="verbatim-42">
grdview us.nc -JM6i -E135/35 -Qi50 -Ius_i.nc -Ctopo.cpt -V -B2 \
 <br />    -JZ0.5i > view.ps
</div>
<!--l. 1834--><p class="nopar" >
</p><!--l. 1837--><p class="noindent" >This plot is pretty crude since we selected 50 dpi but it is fast to render and allows us to try alternate values for
vantage point and scaling. When we settle on the final values we select the appropriate <span
class="ptmri8t-">dpi </span>for the final output
device and let it rip.
</p><!--l. 1843--><p class="noindent" >
</p>
<h5 class="subsubsectionHead"><a
id="x1-610004.5.2"></a>Exercises</h5>
<a
id="dx1-61001"></a>
<!--l. 1846--><p class="noindent" >
</p><ol class="enumerate1" >
<li
class="enumerate" id="x1-61003x1">Choose another vantage point and scaling.
</li>
<li
class="enumerate" id="x1-61005x2">Redo <a
href="../html/man/grdgradient.html" ><span
class="phvb8t-">grdgradient</span></a><a
id="dx1-61006"></a> with another illumination direction and replot.
</li>
<li
class="enumerate" id="x1-61008x3">Select a higher <span
class="ptmri8t-">dpi</span>, e.g., 200.
</li></ol>
<a
id="dx1-61009"></a>
<h2 class="chapterHead"><span class="titlemark">Chapter 5</span><br /><a
id="x1-620005"></a>References</h2>
<ol class="enumerate1" >
<li
class="enumerate" id="x1-62002x1">Smith, W.H.F., and P. Wessel, Gridding with continuous curvature splines in tension, <span
class="ptmri8t-">Geophysics</span>, <span
class="ptmri8t-">55</span>,
293–305, 1990.
</li>
<li
class="enumerate" id="x1-62004x2">Wessel, P., and W.H.F. Smith, Free software helps map and display data, <span
class="ptmri8t-">EOS Trans. AGU</span>, <span
class="ptmri8t-">72</span>, 441,
1991.
</li>
<li
class="enumerate" id="x1-62006x3">Wessel, P., and W.H.F. Smith, New version of the Generic Mapping Tools released, <span
class="ptmri8t-">EOS Trans. AGU</span>,
<span
class="ptmri8t-">76</span>, 329, 1995.
</li>
<li
class="enumerate" id="x1-62008x4">Wessel, P., and W.H.F. Smith, A global, self-consistent, hierarchical, high-resolution shoreline database,
<span
class="ptmri8t-">J. Geophys. Res.</span>, <span
class="ptmri8t-">101</span>, 8741–8743, 1996.
</li>
<li
class="enumerate" id="x1-62010x5">Wessel, P., and W.H.F. Smith, New, improved version of the Generic Mapping Tools released, <span
class="ptmri8t-">EOS</span>
<span
class="ptmri8t-">Trans. AGU</span>, <span
class="ptmri8t-">79</span>, 579, 1998.
</li>
<li
class="enumerate" id="x1-62012x6">Wessel, P., and W.H.F. Smith, The Generic Mapping Tools Technical Reference and Cookbook, <span
class="ptmri8t-">Version</span>
<span
class="ptmri8t-">4.5.11</span>, pp. 227, 2013.
</li></ol>
<div class="footnotes"><!--l. 467--><p class="indent" > <span class="footnote-mark"><a
href="#fn1x1-bk" id="fn1x1"><sup class="textsuperscript">1</sup></a></span><span
class="ptmr8t-x-x-80">See </span><span
class="ptmri8t-x-x-80">Wessel and Smith </span><span
class="ptmr8t-x-x-80">[1996].</span></p>
<!--l. 1311--><p class="indent" > <span class="footnote-mark"><a
href="#fn2x3-bk" id="fn2x3"><sup class="textsuperscript">2</sup></a></span><span
class="ptmr8t-x-x-80">The </span><span
class="pcrb8t-x-x-80">-A</span><span
class="ptmr8t-x-x-80">option is necessary for geographic grids since </span><span
class="ptmri8t-x-x-80">x_inc </span><span
class="ptmr8t-x-x-80">shrinks with latitude. Rule of thumb: set </span><span
class="ptmri8t-x-x-80">aspect </span><span
class="ptmr8t-x-x-80">= cosine of the average</span>
<span
class="ptmr8t-x-x-80">latitude.</span></p> </div>
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