Ubuntu Manpage: grd2cpt - Make linear or histogram-equalized color palette table from grid

Provided by: gmt-common_5.2.1+dfsg-3build1_all

NAME

       grd2cpt - Make linear or histogram-equalized color palette table from grid

SYNOPSIS

       grd2cpt  grid [ [+]transparency ] [ cpt ] [ [i|o] ] [ nlevels ] [ [R|r|h|c ] [ zlo/zhi ] [
       ] [ minlimit/maxlimit ] [  ] [  ] [ [i|o] ] [ region ] [ zstart/zstop/zinc ] [ -|+|_|= ] [
       [level] ] [  ] [  ]

       Note: No space is allowed between the option flag and the associated arguments.

DESCRIPTION

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 wherever values are undefined. For color tables beyond the standard GMT
offerings, visit cpt-city: http://soliton.vm.bytemark.co.uk/pub/cpt-city/.

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 gmt.conf 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 gmt.conf file or on the command line
will be used.

REQUIRED ARGUMENTS

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

OPTIONAL ARGUMENTS

       -A[+]transparency
              Sets  a  constant level of transparency (0-100) for all color slices.  Prepend + to
              also affect the fore-, back-, and nan-colors [Default is no transparency,  i.e.,  0
              (opaque)].

       -Ccpt  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].   Yet  another  option is to specify
              -Ccolor1,color2[,color3,...]  to build a linear continuous CPT  from  those  colors
              automatically.   In  this  case  colorn can be a r/g/b triplet, a color name, or an
              HTML hexadecimal color (e.g. #aabbcc ).

       -D[i|o]
              Select the back- and foreground colors to match the colors for lowest  and  highest
              z-values  in  the  output CPT file [Default uses the colors specified in the master
              file, or those defined by the parameters  COLOR_BACKGROUND,  COLOR_FOREGROUND,  and
              COLOR_NAN].  Append  i to match the colors for the lowest and highest values in the
              input (instead of the output) CPT file.

       -Enlevels
              Create a linear color table by dividing the grid z-range into  nlevels  equidistant
              slices.

       -F[R|r|h|c]
              Force  output CPT file to written with r/g/b codes, gray-scale values or color name
              (R, default) or r/g/b codes only (r), or h-s-v codes (h), or c/m/y/k codes (c).

       -Gzlo/zhi
              Truncate the incoming CPT so that the lowest and highest z-levels are  to  zlo  and
              zhi.   If  one  of  these  equal  NaN then we leave that end of the CPT alone.  The
              truncation takes place before any resampling.

       -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
              COLOR_BACKGROUND and COLOR_FOREGROUND.

       -Lminlimit/maxlimit
              Limit range of CPT file to minlimit/maxlimit, and don't  count  data  outside  this
              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 gmt.conf 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[i|o]
              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[unit]xmin/xmax/ymin/ymax[r] (more ...)
              Specify the region of interest.

       -Szstart/zstop/zinc or -Sn
              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 based on  equidistant
              values  for  a  Gaussian  CDF.   Use  -Sn to select n points from such a cumulative
              normal distribution [11].

       -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 silent.]

       -W     Do not interpolate the input color table but pick the output colors starting at the
              beginning of the map. This is particularly useful in combination with a categorical
              color table. Cannot be used in combination with -Z.

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

       -^ or just -
              Print a short message about the syntax of the command, then exits (NOTE: on Windows
              use just -).

       -+ or just +
              Print  an  extensive  usage  (help)  message,  including  the  explanation  of  any
              module-specific option (but not the GMT common options), then exits.

       -? or no arguments
              Print  a  complete usage (help) message, including the explanation of options, then
              exits.

       --version
              Print GMT version and exit.

       --show-datadir
              Print full path to GMT share directory and exit.

GRID FILE FORMATS

By default GMT writes out grid as single precision floats in a COARDS-complaint netCDF
file format. However, GMT is able to produce grid files in many other commonly used grid
file formats and also facilitates so called "packing" of grids, writing out floating point
data as 1- or 2-byte integers. To specify the precision, scale and offset, the user should
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. In case
the two characters id is not provided, as in =/scale than a id=nf is assumed. When
reading grids, the format is generally automatically recognized. If not, the same suffix
can be added to input grid file names. See grdconvert and Section grid-file-format 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. The ?varname suffix can also be used
for output grids to specify a variable name different from the default: "z". See
grdconvert and Sections modifiers-for-CF and grid-file-format of the GMT Technical
Reference and Cookbook for more information, particularly on how to read splices of 3-,
4-, or 5-dimensional grids.

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):

              gmt grd2cpt mydata.nc -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

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

COPYRIGHT

       2015, P. Wessel, W. H. F. Smith, R. Scharroo, J. Luis, and F. Wobbe