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)