grd2cpt

       grd2cpt - Read a grdfile and make a color palette file

SYNOPSIS

       grd2cpt   grdfile   [  -Ccptmaster  ]  [  -I  ]  [  -Lmin­
       limit/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'  his­
       togram  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  mas­
       ter  cptfile  and colors are sampled at the desired inter­
       vals.

       grdfile
              The 2-D binary grdfile used  to  derive  the  color
              palette table.

OPTIONS

       -C     Selects the master color table to use in the inter­
              polation. 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 mas­
              ter 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):

       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)