NAME
grd2cpt - Read a grdfile and make a color palette file
SYNOPSIS
grd2cpt grdfile [ -Ccptmaster ] [ -I ] [ -Lminlimit/maxlimit
] [ -Szstart/zstop/zinc ] [ -V ] [ -Z ]
DESCRIPTION
grd2cpt reads a grdfile and writes a color palette (cpt)
file to standard output. The cpt file is based on an exist-
ing master cptfile of your choice, and the mapping from data
value to colors is through the data's cumulative distribu-
tion function (CDF), so that the colors are histogram equal-
ized. 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. Let z be
the data values in the grdfile. Define CDF(Z) = (# of z < Z)
/ (# of z in grdfile). (NaNs are ignored). These z-values
are then normalized to the master cptfile and colors are
sampled at the desired intervals.
grdfile
The 2-D binary grdfile used to derive the color palette
table.
OPTIONS
-C Selects the master color table to use in the interpola-
tion. Choose among the built-in tables (type grd2cpt
to see the list) or give the name of an existing
cptfile [Default gives a rainbow cpt file].
-I Reverses the sense of color progression in the master
cptfile.
-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.]
-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.] .TP -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
the built-in master cptfile relief, try
grd2cpt mydata.grd -Crelief -L0/10000 -S0/200/20 >
mydata.cpt
SEE ALSO
gmtdefaults(l), gmt(l), grdhisteq(l), grdinfo(l), makecpt(l)