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.TH "GRD2CPT" "1gmt" "Nov 05, 2016" "5.3.1" "GMT"
.SH NAME
grd2cpt \- Make linear or histogram-equalized color palette table from grid
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.SH SYNOPSIS
.sp
\fBgrd2cpt\fP \fIgrid\fP [  \fB\-A\fP[\fB+\fP]\fItransparency\fP ]
[  \fB\-C\fP\fIcpt\fP ] [  \fB\-D\fP[\fBi\fP|\fBo\fP] ]
[  \fB\-E\fP[\fInlevels\fP] ]
[  \fB\-F\fP[\fBR\fP|\fBr\fP|\fBh\fP|\fBc\fP ][\fB+c\fP]]
[  \fB\-G\fP\fIzlo\fP/\fIzhi\fP ] [  \fB\-I\fP ]
[  \fB\-L\fP\fIminlimit/maxlimit\fP ]
[  \fB\-M\fP ] [  \fB\-N\fP ]
[  \fB\-Q\fP[\fBi\fP|\fBo\fP] ]
[  \fB\-R\fP\fIregion\fP ]
[  \fB\-S\fP\fIzstart/zstop/zinc\fP ]
[  \fB\-T\fP\fB\-\fP|\fB+\fP|\fB_\fP|\fB=\fP ]
[  \fB\-V\fP[\fIlevel\fP] ]
[  \fB\-W\fP ]
[  \fB\-Z\fP ]
.sp
\fBNote:\fP No space is allowed between the option flag and the associated arguments.
.SH DESCRIPTION
.sp
\fBgrd2cpt\fP reads one or more grid files and writes a static color palette
(CPT) file to standard output. The CPT is based on an existing dynamic
master CPT of your choice, and the mapping from data value to
colors is through the data\(aqs cumulative distribution function (CDF), so
that the colors are histogram equalized. Thus if the grid(s) and the
resulting CPT are used in grdimage 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 and colors are sampled at the desired intervals.
.sp
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 \fIz\fP\-value, the foreground color (F) assigned to values
higher than the highest \fIz\fP\-value, and the NaN color (N) painted
wherever values are undefined.  For color tables beyond the
standard GMT offerings, visit cpt\-city:
\fI\%http://soliton.vm.bytemark.co.uk/pub/cpt\-city/\fP\&.
.sp
If the master CPT includes B, F, and N entries, these will be
copied into the new master file. If not, the parameters
COLOR_BACKGROUND, COLOR_FOREGROUND,
and COLOR_NAN from
the gmt.conf file or the command line will be used. This default
behavior can be overruled using the options \fB\-D\fP, \fB\-M\fP or \fB\-N\fP\&.
.sp
The color model (RGB, HSV or CMYK) of the palette created by makecpt
will be the same as specified in the header of the master CPT. When
there is no COLOR_MODEL entry in the master CPT, the
COLOR_MODEL specified in the gmt.conf file or on the command
line will be used.
.SH REQUIRED ARGUMENTS
.INDENT 0.0
.TP
.B \fIgrid\fP
Names of one or more grid files used to derive the color palette
table. All grids need to have the same size and dimensions. (See
GRID FILE FORMATS below).
.UNINDENT
.SH OPTIONAL ARGUMENTS
.INDENT 0.0
.TP
\fB\-A\fP[\fB+\fP]\fItransparency\fP
Sets a constant level of transparency (0\-100) for all color slices.
Prepend \fB+\fP to also affect the fore\-, back\-, and nan\-colors
[Default is no transparency, i.e., 0 (opaque)].
.UNINDENT
.INDENT 0.0
.TP
\fB\-C\fP\fIcpt\fP
Selects the master color table to use in the interpolation. Choose
among the built\-in tables (type \fBgrd2cpt\fP to see the list) or give
the name of an existing CPT [Default gives a rainbow CPT].
Yet another option is to specify \-Ccolor1,color2[,color3,...]
to build a linear continuous CPT from those colors automatically.
In this case \fIcolor\fP\fBn\fP can be a r/g/b triplet, a color name,
or an HTML hexadecimal color (e.g. #aabbcc ).
.UNINDENT
.INDENT 0.0
.TP
\fB\-D\fP[\fBi\fP|\fBo\fP]
Select the back\- and foreground colors to match the colors for
lowest and highest \fIz\fP\-values in the output CPT [Default uses
the colors specified in the master file, or those defined by the
parameters COLOR_BACKGROUND, COLOR_FOREGROUND, and
COLOR_NAN]. Append \fBi\fP to match the colors for the lowest and
highest values in the input (instead of the output) CPT.
.UNINDENT
.INDENT 0.0
.TP
\fB\-E\fP[\fInlevels\fP]
Create a linear color table by using the grid z\-range as the new
limits in the CPT.  Alternatively, append \fInlevels\fP and we will
resample the color table into \fInlevels\fP equidistant slices.
.UNINDENT
.INDENT 0.0
.TP
\fB\-F\fP[\fBR\fP|\fBr\fP|\fBh\fP|\fBc\fP][\fB+c\fP]]
Force output CPT to written with r/g/b codes, gray\-scale values
or color name (\fBR\fP, default) or r/g/b codes only (\fBr\fP), or h\-s\-v
codes (\fBh\fP), or c/m/y/k codes (\fBc\fP).  Optionally or alternatively,
append \fB+c\fP to write discrete palettes in categorical format.
.UNINDENT
.INDENT 0.0
.TP
\fB\-G\fP\fIzlo\fP/\fIzhi\fP
Truncate the incoming CPT so that the lowest and highest z\-levels
are to \fIzlo\fP and \fIzhi\fP\&.  If one of these equal NaN then
we leave that end of the CPT alone.  The truncation takes place
before any resampling.
.UNINDENT
.INDENT 0.0
.TP
\fB\-I\fP
Reverses the sense of color progression in the master CPT. Also
exchanges the foreground and background colors, including those
specified by the parameters COLOR_BACKGROUND and
COLOR_FOREGROUND\&.
.UNINDENT
.INDENT 0.0
.TP
\fB\-L\fP\fIminlimit/maxlimit\fP
Limit range of CPT to \fIminlimit/maxlimit\fP, and don\(aqt count data
outside this range when estimating CDF(Z). [Default uses min and max of data.]
.UNINDENT
.INDENT 0.0
.TP
\fB\-M\fP
Overrule background, foreground, and NaN colors specified in the
master CPT with the values of the parameters
COLOR_BACKGROUND, COLOR_FOREGROUND,
and COLOR_NAN
specified in the gmt.conf file or on the command line. When
combined with \fB\-D\fP, only COLOR_NAN is considered.
.UNINDENT
.INDENT 0.0
.TP
\fB\-N\fP
Do not write out the background, foreground, and NaN\-color fields
[Default will write them].
.UNINDENT
.INDENT 0.0
.TP
\fB\-Q\fP[\fBi\fP|\fBo\fP]
Selects a logarithmic interpolation scheme [Default is linear].
\fB\-Qi\fP expects input z\-values to be log10(z), assigns colors, and
writes out z [Default]. \fB\-Qo\fP takes log10(z) first, assigns
colors, and writes out z.
.UNINDENT
.INDENT 0.0
.TP
\fB\-R\fP[\fIunit\fP]\fIxmin\fP/\fIxmax\fP/\fIymin\fP/\fIymax\fP[\fBr\fP] (more ...)
Specify the region of interest.  
.UNINDENT
.INDENT 0.0
.TP
\fB\-S\fP\fIzstart/zstop/zinc\fP or \fB\-S\fP\fIn\fP
Set steps in CPT. Calculate entries in CPT from \fIzstart\fP
to \fIzstop\fP in steps of (\fIzinc\fP). Default chooses arbitrary values by
a crazy scheme based on equidistant values for a Gaussian CDF.
Use \fB\-S\fP\fIn\fP to select \fIn\fP points from such a
cumulative normal distribution [11].
.UNINDENT
.INDENT 0.0
.TP
\fB\-T\fP\fB\-\fP|\fB+\fP|\fB_\fP|\fB=\fP
Force the color table to be symmetric about zero (from \-R to +R).
Append flag to set the range R: \fB\-\fP for R =|zmin|, \fB+\fP for R =
|zmax|, \fB_\fP for R = min(|zmin|, |zmax|), or \fB=\fP for R =
max(|zmin|, |zmax|).
.UNINDENT
.INDENT 0.0
.TP
\fB\-V\fP
Verbose operation. This will write CDF(Z) estimates to stderr. [Default is silent.]
.UNINDENT
.INDENT 0.0
.TP
\fB\-W\fP
Do not interpolate the input color table but pick the output colors
starting at the beginning of the map. This is particularly useful in
combination with a categorical color table. Cannot be used in
combination with \fB\-Z\fP\&.
.UNINDENT
.INDENT 0.0
.TP
\fB\-Z\fP
Will create a continuous color palette. [Default is discontinuous,
i.e., constant color intervals]
.UNINDENT
.INDENT 0.0
.TP
\fB\-^\fP or just \fB\-\fP
Print a short message about the syntax of the command, then exits (NOTE: on Windows use just \fB\-\fP).
.TP
\fB\-+\fP or just \fB+\fP
Print an extensive usage (help) message, including the explanation of
any module\-specific option (but not the GMT common options), then exits.
.TP
\fB\-?\fP or no arguments
Print a complete usage (help) message, including the explanation of options, then exits.
.UNINDENT
.SH GRID FILE FORMATS
.sp
By default GMT writes out grid as single precision floats in a
COARDS\-complaint netCDF file format. However, GMT is able to produce
grid files in many other commonly used grid file formats and also
facilitates so called "packing" of grids, writing out floating point
data as 1\- or 2\-byte integers. (more ...)
.SH NOTES ON TRANSPARENCY
.sp
The \fIPostScript\fP language originally had no accommodation for transparency.  However, Adobe
added an extension that allows developers to encode some forms of transparency
using the \fIPostScript\fP language model but it is only realized when converting the
\fIPostScript\fP to PDF (and via PDF to any raster image format).
GMT uses this model but there are some limitations: Transparency can only be controlled
on a per\-object or per\-layer basis.  This means that a color specifications (such as
those in CPTs of given via command\-line options) only apply to vector graphic items
(i.e., text, lines, polygon fills) or to an entire layer (which could include items
such as \fIPostScript\fP images).  This limitation rules out any
mechanism of controlling transparency in such images on a pixel level.
.SH COLOR ALIASING
.sp
For best result when \fB\-E\fP is used we recommend you do no append
a specific \fInlevels\fP\&.  This way the original CPT is used exactly
as is but the \fIz\fP boundaries are adjusted to match the grid limits.
Otherwise you may, depending on the nature of the input CPT, miss
aspects of the color changes by aliasing the signal.
.SH EXAMPLES
.sp
Sometimes you don\(aqt want to make a CPT (yet) but would find it
helpful to know that 90% of your data lie between z1 and z2, something
you cannot learn from grdinfo\&. So you can do this to see some points
on the CDF(Z) curve (use \fB\-V\fP option to see more):
.INDENT 0.0
.INDENT 3.5
.INDENT 0.0
.INDENT 3.5
.sp
.nf
.ft C
gmt grd2cpt mydata.nc \-V > /dev/null
.ft P
.fi
.UNINDENT
.UNINDENT
.UNINDENT
.UNINDENT
.sp
To make a CPT 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
.INDENT 0.0
.INDENT 3.5
.INDENT 0.0
.INDENT 3.5
.sp
.nf
.ft C
gmt grd2cpt mydata.nc \-Crelief \-L0/10000 \-S0/200/20 > mydata.cpt
.ft P
.fi
.UNINDENT
.UNINDENT
.UNINDENT
.UNINDENT
.SH SEE ALSO
.sp
gmt, gmt.conf,
grdhisteq, grdinfo, makecpt
.SH COPYRIGHT
2016, P. Wessel, W. H. F. Smith, R. Scharroo, J. Luis, and F. Wobbe
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