Provided by: gmt_4.5.11-1build1_amd64 bug


       grd2cpt - Make a color palette table from grid files


       grd2cpt  grdfiles [ -Ccptmaster ] [ -D ] [ -Enlevels ] [ -I ] [ -Lminlimit/maxlimit ] [ -M
       ] [ -N ] [ -Q[i|o] ] [ -Rwest/east/south/north[r] ] [ -Szstart/zstop/zinc ] [ -T-|+|_|=  ]
       [ -V ] [ -Z ]


       grd2cpt  reads  one  or  more grid files and writes a color palette (cpt) file to standard
       output.  The cpt file is based on an existing master cpt file  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 grid(s) and the  resulting
       cpt  file  are  used  in  grdimage  with a linear projection, the colors will be uniformly
       distributed in area on the plot.  Let z be the data values in the grid.  Define  CDF(Z)  =
       (#  of z < Z) / (# of z in grid).  (NaNs are ignored).  These z-values are then normalized
       to the master cpt file and colors are sampled at the desired intervals.
       The color palette includes three additional colors beyond the range of z-values. These are
       the  background color (B) assigned to values lower than the lowest z-value, the foreground
       color (F) assigned to values higher than the  highest  z-value,  and  the  NaN  color  (N)
       painted whereever values are undefined.
       If  the  master  cpt  file includes B, F, and N entries, these will be copied into the new
       master file.  If not, the parameters  COLOR_BACKGROUND,  COLOR_FOREGROUND,  and  COLOR_NAN
       from the .gmtdefaults4 file or the command line will be used. This default behavior can be
       overruled using the options -D, -M or -N.
       The color model (RGB, HSV or CMYK) of the palette created by makecpt will be the  same  as
       specified  in the header of the master cpt file. When there is no COLOR_MODEL entry in the
       master cpt file, the COLOR_MODEL specified in the .gmtdefaults4 file  or  on  the  command
       line will be used.

              Names  of one or more 2-D binary grid files used to derive the color palette table.
              All grids need to have the same  size  and  dimensions.   (See  GRID  FILE  FORMATS


       -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  cpt
              file [Default gives a rainbow cpt file].

       -D     Select  the  colors  for  lowest and highest z-values in the output cpt file as the
              back- and foreground colors that will be written to the cpt file [Default uses  the
              colors   specified  in  the  master  file,  or  those  defined  by  the  parameters

       -E     Create a linear color table by dividing the grid z-range into  nlevels  equidistant

       -I     Reverses the sense of color progression in the master cpt file.  Also exchanges the
              foreground and background colors,  including  those  specified  by  the  parameters

       -L     Limit  range  of  cpt file to minlimit/maxlimit, and don't count data outside range
              when estimating CDF(Z).  [Default uses min and max of data.]

       -M     Overrule background, foreground, and NaN colors specified in the  master  cpt  file
              with the values of the parameters COLOR_BACKGROUND, COLOR_FOREGROUND, and COLOR_NAN
              specified in the .gmtdefaults4 file or on the command line.  When combined with -D,
              only COLOR_NAN is considered.

       -N     Do  not  write  out  the background, foreground, and NaN-color fields [Default will
              write them].

       -Q     Selects a logarithmic interpolation scheme [Default is linear].  -Qi expects  input
              z-values  to  be  log10(z),  assigns colors, and writes out z [Default].  -Qo takes
              log10(z) first, assigns colors, and writes out z.

       -R     xmin, xmax, ymin, and ymax specify the Region of interest.  For geographic regions,
              these limits correspond to west, east, south, and north and you may specify them in
              decimal degrees or in [+-]dd:mm[][W|E|S|N] format.  Append r if  lower  left
              and  upper  right map coordinates are given instead of w/e/s/n.  The two shorthands
              -Rg and -Rd stand for global domain (0/360 and -180/+180 in longitude respectively,
              with  -90/+90  in  latitude).   Alternatively, specify the name of an existing grid
              file and the -R settings (and grid spacing, if  applicable)  are  copied  from  the
              grid.   For  calendar  time  coordinates  you  may  either  give  (a) relative time
              (relative to the selected TIME_EPOCH and in the selected  TIME_UNIT;  append  t  to
              -JX|x),  or  (b)  absolute time of the form [date]T[clock] (append T to -JX|x).  At
              least one of date and clock must be present; the T is always  required.   The  date
              string must be of the form [-]yyyy[-mm[-dd]] (Gregorian calendar) or yyyy[-Www[-d]]
              (ISO week calendar), while the clock string must be  of  the  form  hh:mm:ss[.xxx].
              The  use  of  delimiters  and their type and positions must be exactly as indicated
              (however, input, output and plot formats are customizable; see gmtdefaults).

       -S     Set steps in cpt file.  Calculate entries in cpt file from zstart to zstop in steps
              of (zinc).  [Default chooses arbitrary values by a crazy scheme.]

       -T     Force  the  color  table to be symmetric about zero (from -R to +R). Append flag to
              set the range R: - for R =|zmin|, + for R = |zmax|, _ for R = min(|zmin|,  |zmax|),
              or = for R = max(|zmin|, |zmax|).

       -V     Verbose  operation.   This  will  write  CDF(Z)  estimates  to stderr.  [Default is

       -Z     Will create a continuous color palette.  [Default is discontinuous, i.e.,  constant
              color intervals]


       GMT  is  able  to  recognize  many  of the commonly used grid file formats, as well as the
       precision, scale and offset of the values contained in the grid file.  When  GMT  needs  a
       little help with that, you can add the suffix =id[/scale/offset[/nan]], where id is a two-
       letter identifier of the grid type and precision, and scale and offset are optional  scale
       factor  and offset to be applied to all grid values, and nan is the value used to indicate
       missing data.  See grdreformat(1) and Section 4.17 of  the  GMT  Technical  Reference  and
       Cookbook for more information.

       When  reading  a  netCDF file that contains multiple grids, GMT will read, by default, the
       first 2-dimensional grid that can find in that file. To  coax  GMT  into  reading  another
       multi-dimensional  variable  in  the  grid  file,  append ?varname to the file name, where
       varname is the name of the variable. Note that you may need to escape the special  meaning
       of  ?  in  your  shell  program  by  putting a backslash in front of it, or by placing the
       filename and suffix between quotes or double quotes.  See grdreformat(1) and Section  4.18
       of  the  GMT Technical Reference and Cookbook for more information, particularly on how to
       read splices of 3-, 4-, or 5-dimensional grids.


       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 cpt file relief, run

       grd2cpt mydata.grd -Crelief -L0/10000 -S0/200/20 > mydata.cpt


       gmtdefaults(1), GMT(1), grdhisteq(1), grdinfo(1), makecpt(1)