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<h1 align=center>GRD2CPT</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="#GRID FILE FORMATS">GRID FILE FORMATS</a><br>
<a href="#EXAMPLES">EXAMPLES</a><br>
<a href="#SEE ALSO">SEE ALSO</a><br>
<hr>
<a name="NAME"></a>
<h2>NAME</h2>
<p style="margin-left:11%; margin-top: 1em">grd2cpt −
Make a color palette table from grid files</p>
<a name="SYNOPSIS"></a>
<h2>SYNOPSIS</h2>
<p style="margin-left:11%; margin-top: 1em"><b>grd2cpt</b>
<i>grdfiles</i> [ <b>−C</b><i>cptmaster</i> ] [
<b>−D</b> ] [ <b>−E</b><i>nlevels</i> ] [
<b>−I</b> ] [ <b>−L</b><i>minlimit/maxlimit</i>
] [ <b>−M</b> ] [ <b>−N</b> ] [
<b>−Q</b>[<b>i|o</b>] ] [
<b>−R</b><i>west</i>/<i>east</i>/<i>south</i>/<i>north</i>[<b>r</b>]
] [ <b>−S</b><i>zstart/zstop/zinc</i> ] [
<b>−T-</b>|<b>+</b>|<b>_</b>|<b>=</b> ] [
<b>−V</b> ] [ <b>−Z</b> ]</p>
<a name="DESCRIPTION"></a>
<h2>DESCRIPTION</h2>
<p style="margin-left:11%; margin-top: 1em"><b>grd2cpt</b>
reads one or more grid files and writes a color palette
(cpt) file to standard output. The cpt file is based on an
existing master cpt file of your choice, and the mapping
from data value to colors is through the data’s
cumulative distribution function (CDF), so that the colors
are histogram equalized. Thus if the grid(s) and the
resulting cpt file are used in <b><A HREF="grdimage.html">grdimage</A></b> with a linear
projection, the colors will be uniformly distributed in area
on the plot. Let z be the data values in the grid. Define
CDF(Z) = (# of z < Z) / (# of z in grid). (NaNs are
ignored). These z-values are then normalized to the master
cpt file and colors are sampled at the desired intervals.
<br>
The color palette includes three additional colors beyond
the range of z-values. These are the background color (B)
assigned to values lower than the lowest <i>z</i>-value, the
foreground color (F) assigned to values higher than the
highest <i>z</i>-value, and the NaN color (N) painted
whereever values are undefined. <br>
If the master cpt file includes B, F, and N entries, these
will be copied into the new master file. If not, the
parameters <b><A HREF="gmtdefaults.html#COLOR_BACKGROUND">COLOR_BACKGROUND</A></b>, <b><A HREF="gmtdefaults.html#COLOR_FOREGROUND">COLOR_FOREGROUND</A></b>,
and <b><A HREF="gmtdefaults.html#COLOR_NAN">COLOR_NAN</A></b> from the .gmtdefaults4 file or the
command line will be used. This default behavior can be
overruled using the options <b>−D</b>, <b>−M</b>
or <b>−N</b>. <br>
The color model (RGB, HSV or CMYK) of the palette created by
<b><A HREF="makecpt.html">makecpt</A></b> will be the same as specified in the header
of the master cpt file. When there is no <b><A HREF="gmtdefaults.html#COLOR_MODEL">COLOR_MODEL</A></b>
entry in the master cpt file, the <b><A HREF="gmtdefaults.html#COLOR_MODEL">COLOR_MODEL</A></b>
specified in the .gmtdefaults4 file or on the command line
will be used. <i><br>
grdfiles</i></p>
<p style="margin-left:22%;">Names of one or more 2-D binary
grid files used to derive the color palette table. All grids
need to have the same size and dimensions. (See GRID FILE
FORMATS below).</p>
<a name="OPTIONS"></a>
<h2>OPTIONS</h2>
<table width="100%" border=0 rules="none" frame="void"
cellspacing="0" cellpadding="0">
<tr valign="top" align="left">
<td width="11%"></td>
<td width="3%">
<p style="margin-top: 1em" valign="top"><b>−C</b></p> </td>
<td width="8%"></td>
<td width="78%">
<p style="margin-top: 1em" valign="top">Selects the master
color table to use in the interpolation. Choose among the
built-in tables (type <b>grd2cpt</b> to see the list) or
give the name of an existing cpt file [Default gives a
rainbow cpt file].</p></td>
<tr valign="top" align="left">
<td width="11%"></td>
<td width="3%">
<p style="margin-top: 1em" valign="top"><b>−D</b></p> </td>
<td width="8%"></td>
<td width="78%">
<p style="margin-top: 1em" valign="top">Select the colors
for lowest and highest <i>z</i>-values in the output cpt
file as the back- and foreground colors that will be written
to the cpt file [Default uses the colors specified in the
master file, or those defined by the parameters
<b><A HREF="gmtdefaults.html#COLOR_BACKGROUND">COLOR_BACKGROUND</A></b>, <b><A HREF="gmtdefaults.html#COLOR_FOREGROUND">COLOR_FOREGROUND</A></b>, and
<b><A HREF="gmtdefaults.html#COLOR_NAN">COLOR_NAN</A></b>].</p> </td>
<tr valign="top" align="left">
<td width="11%"></td>
<td width="3%">
<p style="margin-top: 1em" valign="top"><b>−E</b></p> </td>
<td width="8%"></td>
<td width="78%">
<p style="margin-top: 1em" valign="top">Create a linear
color table by dividing the grid z-range into <i>nlevels</i>
equidistant slices.</p></td>
<tr valign="top" align="left">
<td width="11%"></td>
<td width="3%">
<p style="margin-top: 1em" valign="top"><b>−I</b></p> </td>
<td width="8%"></td>
<td width="78%">
<p style="margin-top: 1em" valign="top">Reverses the sense
of color progression in the master cpt file. Also exchanges
the foreground and background colors, including those
specified by the parameters <b><A HREF="gmtdefaults.html#COLOR_BACKGROUND">COLOR_BACKGROUND</A></b> and
<b><A HREF="gmtdefaults.html#COLOR_FOREGROUND">COLOR_FOREGROUND</A></b>.</p> </td>
<tr valign="top" align="left">
<td width="11%"></td>
<td width="3%">
<p style="margin-top: 1em" valign="top"><b>−L</b></p> </td>
<td width="8%"></td>
<td width="78%">
<p style="margin-top: 1em" valign="top">Limit range of cpt
file to <i>minlimit/maxlimit</i>, and don’t count data
outside range when estimating CDF(Z). [Default uses min and
max of data.]</p></td>
<tr valign="top" align="left">
<td width="11%"></td>
<td width="3%">
<p style="margin-top: 1em" valign="top"><b>−M</b></p> </td>
<td width="8%"></td>
<td width="78%">
<p style="margin-top: 1em" valign="top">Overrule
background, foreground, and NaN colors specified in the
master cpt file with the values of the parameters
<b><A HREF="gmtdefaults.html#COLOR_BACKGROUND">COLOR_BACKGROUND</A></b>, <b><A HREF="gmtdefaults.html#COLOR_FOREGROUND">COLOR_FOREGROUND</A></b>, and
<b><A HREF="gmtdefaults.html#COLOR_NAN">COLOR_NAN</A></b> specified in the .gmtdefaults4 file or on
the command line. When combined with <b>−D</b>, only
<b><A HREF="gmtdefaults.html#COLOR_NAN">COLOR_NAN</A></b> is considered.</p></td>
<tr valign="top" align="left">
<td width="11%"></td>
<td width="3%">
<p style="margin-top: 1em" valign="top"><b>−N</b></p> </td>
<td width="8%"></td>
<td width="78%">
<p style="margin-top: 1em" valign="top">Do not write out
the background, foreground, and NaN-color fields [Default
will write them].</p></td>
<tr valign="top" align="left">
<td width="11%"></td>
<td width="3%">
<p style="margin-top: 1em" valign="top"><b>−Q</b></p> </td>
<td width="8%"></td>
<td width="78%">
<p style="margin-top: 1em" valign="top">Selects a
logarithmic interpolation scheme [Default is linear].
<b>−Qi</b> expects input z-values to be log10(z),
assigns colors, and writes out z [Default]. <b>−Qo</b>
takes log10(z) first, assigns colors, and writes out z.</p></td>
<tr valign="top" align="left">
<td width="11%"></td>
<td width="3%">
<p style="margin-top: 1em" valign="top"><b>−R</b></p> </td>
<td width="8%"></td>
<td width="78%">
<p style="margin-top: 1em" valign="top"><i>xmin</i>,
<i>xmax</i>, <i>ymin</i>, and <i>ymax</i> specify the Region
of interest. For geographic regions, these limits correspond
to <i>west, east, south,</i> and <i>north</i> 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>−Rg</b> and
<b>−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>−R</b> settings (and grid
spacing, if applicable) are copied from the grid. For
calendar time coordinates you may either give (a) relative
time (relative to the selected <b><A HREF="gmtdefaults.html#TIME_EPOCH">TIME_EPOCH</A></b> and in the
selected <b><A HREF="gmtdefaults.html#TIME_UNIT">TIME_UNIT</A></b>; append <b>t</b> to
<b>−JX</b>|<b>x</b>), or (b) absolute time of the form
[<i>date</i>]<b>T</b>[<i>clock</i>] (append <b>T</b> to
<b>−JX</b>|<b>x</b>). At least one of <i>date</i> and
<i>clock</i> must be present; the <b>T</b> is always
required. The <i>date</i> string must be of the form
[-]yyyy[-mm[-dd]] (Gregorian calendar) or yyyy[-Www[-d]]
(ISO week calendar), while the <i>clock</i> string must be
of the form hh:mm:ss[.xxx]. The use of delimiters and their
type and positions must be exactly as indicated (however,
input, output and plot formats are customizable; see
<b><A HREF="gmtdefaults.html">gmtdefaults</A></b>).</p> </td>
<tr valign="top" align="left">
<td width="11%"></td>
<td width="3%">
<p style="margin-top: 1em" valign="top"><b>−S</b></p> </td>
<td width="8%"></td>
<td width="78%">
<p style="margin-top: 1em" valign="top">Set steps in cpt
file. Calculate entries in cpt file from <i>zstart</i> to
<i>zstop</i> in steps of (<i>zinc</i>). [Default chooses
arbitrary values by a crazy scheme.]</p></td>
<tr valign="top" align="left">
<td width="11%"></td>
<td width="3%">
<p style="margin-top: 1em" valign="top"><b>−T</b></p> </td>
<td width="8%"></td>
<td width="78%">
<p style="margin-top: 1em" valign="top">Force the color
table to be symmetric about zero (from -R to +R). Append
flag to set the range R: <b>-</b> for R =|zmin|, <b>+</b>
for R = |zmax|, <b>_</b> for R = min(|zmin|, |zmax|), or
<b>=</b> for R = max(|zmin|, |zmax|).</p></td>
<tr valign="top" align="left">
<td width="11%"></td>
<td width="3%">
<p style="margin-top: 1em" valign="top"><b>−V</b></p> </td>
<td width="8%"></td>
<td width="78%">
<p style="margin-top: 1em" valign="top">Verbose operation.
This will write CDF(Z) estimates to stderr. [Default is
silent.]</p> </td>
<tr valign="top" align="left">
<td width="11%"></td>
<td width="3%">
<p style="margin-top: 1em" valign="top"><b>−Z</b></p> </td>
<td width="8%"></td>
<td width="78%">
<p style="margin-top: 1em" valign="top">Will create a
continuous color palette. [Default is discontinuous, i.e.,
constant color intervals]</p></td>
</table>
<a name="GRID FILE FORMATS"></a>
<h2>GRID FILE FORMATS</h2>
<p style="margin-left:11%; margin-top: 1em"><b><A HREF="GMT.html">GMT</A></b> is
able to recognize many of the commonly used grid file
formats, as well as the precision, scale and offset of the
values contained in the grid file. When <b><A HREF="GMT.html">GMT</A></b> needs a
little help with that, you can add the suffix
<b>=</b><i>id</i>[<b>/</b><i>scale</i><b>/</b><i>offset</i>[<b>/</b><i>nan</i>]],
where <i>id</i> is a two-letter identifier of the grid type
and precision, and <i>scale</i> and <i>offset</i> are
optional scale factor and offset to be applied to all grid
values, and <i>nan</i> is the value used to indicate missing
data. See <b><A HREF="grdreformat.html">grdreformat</A></b>(1) and Section 4.17 of the GMT
Technical Reference and Cookbook for more information.</p>
<p style="margin-left:11%; margin-top: 1em">When reading a
netCDF file that contains multiple grids, <b><A HREF="GMT.html">GMT</A></b> will
read, by default, the first 2-dimensional grid that can find
in that file. To coax <b><A HREF="GMT.html">GMT</A></b> into reading another
multi-dimensional variable in the grid file, append
<b>?</b><i>varname</i> to the file name, where
<i>varname</i> is the name of the variable. Note that you
may need to escape the special meaning of <b>?</b> in your
shell program by putting a backslash in front of it, or by
placing the filename and suffix between quotes or double
quotes. See <b><A HREF="grdreformat.html">grdreformat</A></b>(1) and Section 4.18 of the
GMT Technical Reference and Cookbook for more information,
particularly on how to read splices of 3-, 4-, or
5-dimensional grids.</p>
<a name="EXAMPLES"></a>
<h2>EXAMPLES</h2>
<p style="margin-left:11%; margin-top: 1em">Sometimes you
don’t want to make a cpt file (yet) but would find it
helpful to know that 90% of your data lie between z1 and z2,
something you cannot learn from <b><A HREF="grdinfo.html">grdinfo</A></b>. So you can
do this to see some points on the CDF(Z) curve (use
<b>−V</b> option to see more):</p>
<p style="margin-left:11%; margin-top: 1em"><b>grd2cpt</b>
mydata.grd <b>−V</b> > /dev/null</p>
<p style="margin-left:11%; margin-top: 1em">To make a cpt
file with entries from 0 to 200 in steps of 20, and ignore
data below zero in computing CDF(Z), and use the built-in
master cpt file relief, run</p>
<p style="margin-left:11%; margin-top: 1em"><b>grd2cpt</b>
mydata.grd <b>−C</b><i>relief</i> <b>-L</b>0/10000
<b>-S</b>0/200/20 > mydata.cpt</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="grdhisteq.html">grdhisteq</A></i>(1), <i><A HREF="grdinfo.html">grdinfo</A></i>(1),
<i><A HREF="makecpt.html">makecpt</A></i>(1)</p>
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