GRD2CPT
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NAME
grd2cpt - Read a grdfile and make a color palette file
SYNOPSIS
grd2cpt grdfile [ -Cminhue/maxhue ] [ -Lminlimit/maxlimit ]
[ -Mmingray/maxgray ] [ -Szstart/zstop/zinc ] [ -V ]
DESCRIPTION
grd2cpt reads a grdfile and writes a color palette (cpt) file to standard output.
The cpt file has continuously changing hue (or gray level) and the mapping from
data value to hue (or gray level) 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. A simple linear transform from
data to hue (or gray level) is not provided here because that can be made with
makecpt or awk.
Let z be the data values in the grdfile. Define CDF(Z) = (# of z < Z) / (# of z in
grdfile). (NaNs are ignored). Then hue(Z) = minhue + (maxhue - minhue) *
CDF(Z), or the equivalent with mingray/maxgray.
- grdfile
-
The 2-D binary grdfile used to derive the color palette table.
OPTIONS
- -C
-
Color option. Set hues to use at lowest (minhue) and highest (maxhue)
end of cpt range. [Default is 300/0, i.e. magenta/red].
- -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.]
- -M
-
Monochrome option. Set gray levels (on a scale from 0=black to 1=white) to use at
lowest (mingray) and highest (maxgray) end of cpt range. [Default is
color output.]
- -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.]
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 hues from dark purple (260) to orange (30), try
grd2cpt mydata.grd -C260/30 -L0/10000 -S0/200/20 > mydata.cpt
SEE ALSO
gmtdefaults, gmt, grdhisteq, grdinfo, makecpt
#include "refs.i"
Index
- NAME
-
- SYNOPSIS
-
- DESCRIPTION
-
- OPTIONS
-
- EXAMPLES
-
- SEE ALSO
-
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