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)



GMT3.4.6                          1 Jan 2005                        GRD2CPT(l)

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