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<h1 align=center>GRDRASTER</h1>

<a href="#NAME">NAME</a><br>
<a href="#SYNOPSIS">SYNOPSIS</a><br>
<a href="#DESCRIPTION">DESCRIPTION</a><br>
<a href="#OPTIONS">OPTIONS</a><br>
<a href="#EXAMPLES">EXAMPLES</a><br>
<a href="#SEE ALSO">SEE ALSO</a><br>
<a href="#REFERENCES">REFERENCES</a><br>

<hr>


<a name="NAME"></a>
<h2>NAME</h2>


<p style="margin-left:11%; margin-top: 1em">grdraster
&minus; extract subregion from a binary raster and write a
grid file</p>

<a name="SYNOPSIS"></a>
<h2>SYNOPSIS</h2>



<p style="margin-left:11%; margin-top: 1em"><b>grdraster</b>
[ <i>filenumber</i> | <i>&quot;text pattern&quot;</i> ]
<b>&minus;R</b><i>west</i>/<i>east</i>/<i>south</i>/<i>north</i>[<b>r</b>]
[ <b>&minus;G</b><i>grdfile</i> ] [
<b>&minus;I</b><i>xinc</i>[<b>m</b>|<b>c</b>][/<i>yinc</i>[<b>m</b>|<b>c</b>]]
] [ <b>&minus;J</b><i>parameters</i> ] [ <b>&minus;V</b> ] [
<b>&minus;bo</b>[<b>s</b>|<b>S</b>|<b>d</b>|<b>D</b>[<i>ncol</i>]|<b>c</b>[<i>var1</i><b>/</b><i>...</i>]]
]</p>

<a name="DESCRIPTION"></a>
<h2>DESCRIPTION</h2>



<p style="margin-left:11%; margin-top: 1em"><b>grdraster</b>
reads a file called <i>grdraster.info</i> from the current
working directory, the directories pointed to by the
environment variables <b>$GMT_DATADIR</b> and
<b>$GMT_USERDIR</b>, or in <b>$GMT_SHAREDIR</b>/dbase (in
that order). The file <i>grdraster.info</i> defines binary
arrays of data stored in scan-line format in data files.
Each file is given a <i>filenumber</i> in the info file.
<b>grdraster</b> figures out how to load the raster data
into a grid file spanning a region defined by
<b>&minus;R</b>. By default the grid spacing equals the
raster spacing. The <b>&minus;I</b> option may be used to
sub-sample the raster data. No filtering or interpolating is
done, however; the <i>x_inc</i> and <i>y_inc</i> of the grid
must be multiples of the increments of the raster file and
<b>grdraster</b> simply takes every n&rsquo;th point. The
output of <b>grdraster</b> is either grid or pixel
registered depending on the registration of the raster used.
It is up to the <b><A HREF="GMT.html">GMT</A></b> system person to maintain the
<i>grdraster.info</i> file in accordance with the available
rasters at each site. Raster data sets are not supplied with
<b><A HREF="GMT.html">GMT</A></b> but can be obtained by anonymous ftp and on
CD-ROM (see README page in dbase directory).
<b>grdraster</b> will list the available files if no
arguments are given. Finally, <b>grdraster</b> will write
xyz-triplets to stdout if no output gridfile name is given
<i><br>
filenumber</i></p>

<p style="margin-left:22%;">If an integer matching one of
the files listed in the <i>grdraster.info</i> file is given
we will use that data set, else we will match the given text
pattern with the data set description in order to determine
the data set.</p>

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<p style="margin-top: 1em" valign="top"><b>&minus;R</b></p> </td>
<td width="8%"></td>
<td width="78%">


<p style="margin-top: 1em" valign="top"><i>west, east,
south,</i> and <i>north</i> specify the Region of interest,
and you may specify them in decimal degrees or in
[+-]dd:mm[:ss.xxx][W|E|S|N] format. Append <b>r</b> if lower
left and upper right map coordinates are given instead of
w/e/s/n. The two shorthands <b>&minus;Rg</b> and
<b>&minus;Rd</b> stand for global domain (0/360 and
-180/+180 in longitude respectively, with -90/+90 in
latitude). Alternatively, specify the name of an existing
grid file and the <b>&minus;R</b> settings (and grid
spacing, if applicable) are copied from the grid. If
<b>r</b> is appended, you may also specify a map projection
to define the shape of your region. The output region will
be rounded off to the nearest whole grid-step in both
dimensions.</p> </td>
</table>

<a name="OPTIONS"></a>
<h2>OPTIONS</h2>


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<p style="margin-top: 1em" valign="top"><b>&minus;G</b></p> </td>
<td width="8%"></td>
<td width="78%">


<p style="margin-top: 1em" valign="top">Name of output grid
file. If not set, the grid will be written as ASCII (or
binary; see <b>&minus;bo</b> xyz-triplets to stdout
instead.</p> </td>
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<p style="margin-top: 1em" valign="top"><b>&minus;I</b></p> </td>
<td width="8%"></td>
<td width="78%">


<p style="margin-top: 1em" valign="top"><i>x_inc</i> [and
optionally <i>y_inc</i>] is the grid spacing. Optionally,
append a suffix modifier. <b>Geographical (degrees)
coordinates</b>: Append <b>m</b> to indicate arc minutes or
<b>c</b> to indicate arc seconds. If one of the units
<b>e</b>, <b>k</b>, <b>i</b>, or <b>n</b> is appended
instead, the increment is assumed to be given in meter, km,
miles, or nautical miles, respectively, and will be
converted to the equivalent degrees longitude at the middle
latitude of the region (the conversion depends on
<b><A HREF="gmtdefaults.html#ELLIPSOID">ELLIPSOID</A></b>). If /<i>y_inc</i> is given but set to 0 it
will be reset equal to <i>x_inc</i>; otherwise it will be
converted to degrees latitude. <b>All coordinates</b>: If
<b>=</b> is appended then the corresponding max <i>x</i>
(<i>east</i>) or <i>y</i> (<i>north</i>) may be slightly
adjusted to fit exactly the given increment [by default the
increment may be adjusted slightly to fit the given domain].
Finally, instead of giving an increment you may specify the
<i>number of nodes</i> desired by appending <b>+</b> to the
supplied integer argument; the increment is then
recalculated from the number of nodes and the domain. The
resulting increment value depends on whether you have
selected a gridline-registered or pixel-registered grid; see
Appendix B for details. Note: if
<b>&minus;R</b><i>grdfile</i> is used then grid spacing has
already been initialized; use <b>&minus;I</b> to override
the values.</p></td>
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<p style="margin-top: 1em" valign="top"><b>&minus;J</b></p> </td>
<td width="8%"></td>
<td width="78%">


<p style="margin-top: 1em" valign="top">Selects the map
projection. Scale is UNIT/degree, 1:xxxxx, or width in UNIT
(upper case modifier). UNIT is cm, inch, or m, depending on
the <b><A HREF="gmtdefaults.html#MEASURE_UNIT">MEASURE_UNIT</A></b> setting in .gmtdefaults4, but this
can be overridden on the command line by appending <b>c</b>,
<b>i</b>, or <b>m</b> to the scale/width value. When central
meridian is optional, default is center of longitude range
on <b>&minus;R</b> option. Default standard parallel is the
equator. For map height, max dimension, or min dimension,
append <b>h</b>, <b>+</b>, or <b>-</b> to the width,
respectively.</p> </td>
</table>

<p style="margin-left:22%;">More details can be found in
the <b><A HREF="psbasemap.html">psbasemap</A></b> man pages.</p>

<p style="margin-left:22%; margin-top: 1em"><b>CYLINDRICAL
PROJECTIONS:</b></p>


<p style="margin-left:22%; margin-top: 1em"><b>&minus;Jc</b><i>lon0/lat0/scale</i>
(Cassini) <b><br>

&minus;Jcyl_stere</b>/[<i>lon0/</i>[<i>lat0/</i>]]<i>scale</i>
(Cylindrical Stereographic) <b><br>
&minus;Jj</b>[<i>lon0/</i>]<i>scale</i> (Miller) <b><br>
&minus;Jm</b>[<i>lon0</i>/[<i>lat0/</i>]]<i>scale</i>
(Mercator) <b><br>
&minus;Jm</b><i>lon0/lat0/scale</i> (Mercator - Give
meridian and standard parallel) <b><br>
&minus;Jo</b>[<b>a</b>]<i>lon0/lat0/azimuth/scale</i>
(Oblique Mercator - point and azimuth) <b><br>
&minus;Jo</b>[<b>b</b>]<i>lon0/lat0/lon1/lat1/scale</i>
(Oblique Mercator - two points) <b><br>
&minus;Joc</b><i>lon0/lat0/lonp/latp/scale</i> (Oblique
Mercator - point and pole) <b><br>
&minus;Jq</b>[<i>lon0/</i>[<i>lat0/</i>]]<i>scale</i>
(Cylindrical Equidistant) <b><br>
&minus;Jt</b><i>lon0/</i>[<i>lat0/</i>]<i>scale</i> (TM -
Transverse Mercator) <b><br>
&minus;Ju</b><i>zone/scale</i> (UTM - Universal Transverse
Mercator) <b><br>
&minus;Jy</b>[<i>lon0/</i>[<i>lat0/</i>]]<i>scale</i>
(Cylindrical Equal-Area)</p>

<p style="margin-left:22%; margin-top: 1em"><b>CONIC
PROJECTIONS:</b></p>


<p style="margin-left:22%; margin-top: 1em"><b>&minus;Jb</b><i>lon0/lat0/lat1/lat2/scale</i>
(Albers) <b><br>
&minus;Jd</b><i>lon0/lat0/lat1/lat2/scale</i> (Conic
Equidistant) <b><br>
&minus;Jl</b><i>lon0/lat0/lat1/lat2/scale</i> (Lambert Conic
Conformal) <b><br>
&minus;Jpoly</b>/[<i>lon0/</i>[<i>lat0/</i>]]<i>scale</i>
((American) Polyconic)</p>

<p style="margin-left:22%; margin-top: 1em"><b>AZIMUTHAL
PROJECTIONS:</b></p>


<p style="margin-left:22%; margin-top: 1em"><b>&minus;Ja</b><i>lon0/lat0</i>[<i>/horizon</i>]<i>/scale</i>
(Lambert Azimuthal Equal-Area) <b><br>
&minus;Je</b><i>lon0/lat0</i>[<i>/horizon</i>]<i>/scale</i>
(Azimuthal Equidistant) <b><br>
&minus;Jf</b><i>lon0/lat0</i>[<i>/horizon</i>]<i>/scale</i>
(Gnomonic) <b><br>
&minus;Jg</b><i>lon0/lat0</i>[<i>/horizon</i>]<i>/scale</i>
(Orthographic) <b><br>

&minus;Jg</b><i>lon0/lat0/altitude/azimuth/tilt/twist/Width/Height/scale</i>
(General Perspective). <b><br>
&minus;Js</b><i>lon0/lat0</i>[<i>/horizon</i>]<i>/scale</i>
(General Stereographic)</p>


<p style="margin-left:22%; margin-top: 1em"><b>MISCELLANEOUS
PROJECTIONS:</b></p>


<p style="margin-left:22%; margin-top: 1em"><b>&minus;Jh</b>[<i>lon0/</i>]<i>scale</i>
(Hammer) <b><br>
&minus;Ji</b>[<i>lon0/</i>]<i>scale</i> (Sinusoidal) <b><br>
&minus;Jkf</b>[<i>lon0/</i>]<i>scale</i> (Eckert IV) <b><br>
&minus;Jk</b>[<b>s</b>][<i>lon0/</i>]<i>scale</i> (Eckert
VI) <b><br>
&minus;Jn</b>[<i>lon0/</i>]<i>scale</i> (Robinson) <b><br>
&minus;Jr</b>[<i>lon0/</i>]<i>scale</i> (Winkel Tripel)
<b><br>
&minus;Jv</b>[<i>lon0/</i>]<i>scale</i> (Van der Grinten)
<b><br>
&minus;Jw</b>[<i>lon0/</i>]<i>scale</i> (Mollweide)</p>


<p style="margin-left:22%; margin-top: 1em"><b>NON-GEOGRAPHICAL
PROJECTIONS:</b></p>


<p style="margin-left:22%; margin-top: 1em"><b>&minus;Jp</b>[<b>a</b>]<i>scale</i>[<i>/origin</i>][<b>r</b>|<b>z</b>]
(Polar coordinates (theta,r)) <b><br>

&minus;Jx</b><i>x-scale</i>[<b>d</b>|<b>l</b>|<b>p</b><i>pow</i>|<b>t</b>|<b>T</b>][<i>/y-scale</i>[<b>d</b>|<b>l</b>|<b>p</b><i>pow</i>|<b>t</b>|<b>T</b>]]
(Linear, log, and power scaling)</p>

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<p style="margin-top: 1em" valign="top"><b>&minus;V</b></p> </td>
<td width="7%"></td>
<td width="78%">


<p style="margin-top: 1em" valign="top">Selects verbose
mode, which will send progress reports to stderr [Default
runs &quot;silently&quot;].</p></td>
<tr valign="top" align="left">
<td width="11%"></td>
<td width="4%">



<p style="margin-top: 1em" valign="top"><b>&minus;bo</b></p> </td>
<td width="7%"></td>
<td width="78%">


<p style="margin-top: 1em" valign="top">Selects binary
output. Append <b>s</b> for single precision [Default is
<b>d</b> (double)]. Uppercase <b>S</b> or <b>D</b> will
force byte-swapping. Optionally, append <i>ncol</i>, the
number of desired columns in your binary output file. This
option applies only if no <b>&minus;G</b> option has been
set.</p> </td>
</table>

<a name="EXAMPLES"></a>
<h2>EXAMPLES</h2>


<p style="margin-left:11%; margin-top: 1em">To extract data
from raster 1, taking one point every 30 minutes, in an area
extended beyond 360 degrees to allow later filtering,
run</p>


<p style="margin-left:11%; margin-top: 1em"><b>grdraster</b>
1 <b>&minus;R</b>-4/364/-62/62 <b>&minus;I</b> 30<b>m
&minus;G</b> data.grd</p>

<p style="margin-left:11%; margin-top: 1em">To obtain data
for an oblique Mercator projection we need to extract more
data that is actually used. This is necessary because the
output of <b>grdraster</b> has edges defined by parallels
and meridians, while the oblique map in general does not.
Hence, to get all the data from the ETOPO2 data needed to
make a contour map for the region defined by its lower left
and upper right corners and the desired projection, use</p>


<p style="margin-left:11%; margin-top: 1em"><b>grdraster</b>
ETOPO2 <b>&minus;R</b> 160/20/220/30<b>r &minus;Joc</b>
190/25.5/292/69/1 <b>&minus;G</b> data.grd</p>

<p style="margin-left:11%; margin-top: 1em">To extract data
from the 2 min Geoware relief blend and write it as binary
double precision xyz-triplets to standard output:</p>


<p style="margin-left:11%; margin-top: 1em"><b>grdraster</b>
&quot;2 min Geoware&quot; <b>&minus;R</b> 20/25/-10/5
<b>&minus;bo</b> &gt;! triplets.b</p>

<a name="SEE ALSO"></a>
<h2>SEE ALSO</h2>



<p style="margin-left:11%; margin-top: 1em"><i><A HREF="gmtdefaults.html">gmtdefaults</A></i>(1),
<i><A HREF="GMT.html">GMT</A></i>(1), <i><A HREF="grdsample.html">grdsample</A></i>(1), <i><A HREF="grdfilter.html">grdfilter</A></i>(1)</p>

<a name="REFERENCES"></a>
<h2>REFERENCES</h2>


<p style="margin-left:11%; margin-top: 1em">Wessel, P., and
W. H. F. Smith, 2013, The Generic Mapping Tools (GMT)
version 4.5.11 Technical Reference &amp; Cookbook,
SOEST/NOAA. <br>
Wessel, P., and W. H. F. Smith, 1998, New, Improved Version
of Generic Mapping Tools Released, EOS Trans., AGU, 79 (47),
p. 579. <br>
Wessel, P., and W. H. F. Smith, 1995, New Version of the
Generic Mapping Tools Released, EOS Trans., AGU, 76 (33), p.
329. <br>
Wessel, P., and W. H. F. Smith, 1995, New Version of the
Generic Mapping Tools Released,
http://www.agu.org/eos_elec/95154e.html, Copyright 1995 by
the American Geophysical Union. <br>
Wessel, P., and W. H. F. Smith, 1991, Free Software Helps
Map and Display Data, EOS Trans., AGU, 72 (41), p. 441.</p>
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