NAME

       grd2cpt - Read a grdfile and make a color palette file


SYNOPSIS

       grd2cpt  grdfile [ -Ccptmaster ] [ -I ] [ -Lminlimit/maxlimit ] [ -Szs-
       tart/zstop/zinc ] [ -V ] [ -Z ]


DESCRIPTION

       grd2cpt reads a grdfile and writes a color palette (cpt) file to  stan-
       dard  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 uni-
       formly 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 discontinu-
              ous, 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(l), gmt(l), grdhisteq(l), grdinfo(l), makecpt(l)



VERSION                              DATE                           GRD2CPT(l)

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