GRD2CPT(l)																GRD2CPT(l)

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 existing master cptfile 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 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 interpolation. 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.]

       -V     Verbose operation. This will write CDF(Z) estimates to stderr. [Default is silent.]

       -Z     Will create a continuous color palette.  [Default is discontinuous, i.e., constant color intervals]

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(1gmt), gmt(1gmt), grdhisteq(1gmt), grdinfo(1gmt), makecpt(1gmt)

								    1 Jan 2004								GRD2CPT(l)