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)