GRD2CPT

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NAME

grd2cpt - Read a grdfile and make a color palette file  

SYNOPSIS

grd2cpt grdfile [ -Cminhue/maxhue ] [ -Lminlimit/maxlimit ]
 [ -Mmingray/maxgray ] [ -Szstart/zstop/zinc ] [ -V ]  

DESCRIPTION

grd2cpt reads a grdfile and writes a color palette (cpt) file to standard output. The cpt file has continuously changing hue (or gray level) and the mapping from data value to hue (or gray level) is through the data's cumulative distribution function (CDF), so that the colors are histogram equalized. Thus if the resulting cpt file is used with the grdfile and grdimage with a linear projection, the colors will be uniformly distributed in area on the plot. A simple linear transform from data to hue (or gray level) is not provided here because that can be made with makecpt or awk. Let z be the data values in the grdfile. Define CDF(Z) = (# of z < Z) / (# of z in grdfile). (NaNs are ignored). Then hue(Z) = minhue + (maxhue - minhue) * CDF(Z), or the equivalent with mingray/maxgray.
grdfile
The 2-D binary grdfile used to derive the color palette table.
 

OPTIONS

-C
Color option. Set hues to use at lowest (minhue) and highest (maxhue) end of cpt range. [Default is 300/0, i.e. magenta/red].
-L
Limit range of cptfile to minlimit/maxlimit, and don't count data outside range when estimating CDF(Z). [Default uses min and max of data.]
-M
Monochrome option. Set gray levels (on a scale from 0=black to 1=white) to use at lowest (mingray) and highest (maxgray) end of cpt range. [Default is color output.]
-S
Set steps in cpt file. Calculate entries in cptfile from zstart to zstop in steps of (zinc). [Default chooses arbitrary values by a crazy scheme.]
-V
Verbose operation. This will write CDF(Z) estimates to stderr. [Default is silent.]
 

EXAMPLES

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 grdinfo. So you can do this to see some points on the CDF(Z) curve (use -V option to see more):

grd2cpt mydata.grd -V > /dev/null

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 hues from dark purple (260) to orange (30), try

grd2cpt mydata.grd -C260/30 -L0/10000 -S0/200/20 > mydata.cpt  

SEE ALSO

gmtdefaults, gmt, grdhisteq, grdinfo, makecpt #include "refs.i"


 

Index

NAME
SYNOPSIS
DESCRIPTION
OPTIONS
EXAMPLES
SEE ALSO

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Time: 07:11:07 GMT, January 07, 2025