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)