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grdcut(1gmt)

NAME

   grdcut - Extract subregion from a grid

SYNOPSIS

   grdcut ingrid  -Goutgrid
    -Rregion [  -N[nodata] ] [  -S[n]lon/lat/radius[unit] ] [  -V[level] ]
   [  -Z[n|r]min/max ] [ -fflags ]

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

DESCRIPTION

   grdcut  will produce a new outgrid file which is a subregion of ingrid.
   The subregion is specified with -R as in other programs; the  specified
   range  must  not exceed the range of ingrid (but see -N).  If in doubt,
   run  grdinfo  to  check  range.  Alternatively,  define  the  subregion
   indirectly via a range check on the node values or via distances from a
   given point. Complementary to grdcut there is grdpaste, which will join
   together two grid files along a common edge.

REQUIRED ARGUMENTS

   ingrid This is the input grid file.

   -Goutgrid
          This is the output grid file.

OPTIONAL ARGUMENTS

   -N[nodata]
          Allow grid to be extended if new -R exceeds existing boundaries.
          Append nodata value to initialize nodes outside  current  region
          [Default is NaN].

   -R[unit]xmin/xmax/ymin/ymax[r] (more ...)
          Specify the region of interest. This defines the subregion to be
          cut out.

   -S[n]lon/lat/radius[unit]
          Specify an origin and radius; append a distance unit (see UNITS)
          and  we  determine  the corresponding rectangular region so that
          all grid nodes on or inside the  circle  are  contained  in  the
          subset.  If  -Sn  is used we set all nodes outside the circle to
          NaN.

   -V[level] (more ...)
          Select verbosity level [c].

   -Z[n|r]min/max
          Determine the new rectangular region so that all  nodes  outside
          this  region  are also outside the given z-range [-inf/+inf]. To
          indicate no limit on min or max, specify a hyphen (-). Normally,
          any  NaNs  encountered  are simply skipped and not considered in
          the decision.  Use -Zn to consider  a  NaN  to  be  outside  the
          z-range.   This   means   the   new  subset  will  be  NaN-free.
          Alternatively, use -Zr to consider NaNs to be  within  the  data
          range.  In this case we stop shrinking the boundaries once a NaN
          is found [Default  simply  skips  NaNs  when  making  the  range
          decision].

   -f[i|o]colinfo (more ...)
          Specify data types of input and/or output columns.

   -^ 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.

UNITS

   For  map distance unit, append unit d for arc degree, m for arc minute,
   and s for arc second, or e for meter [Default], f for foot, k for km, M
   for  statute  mile,  n  for nautical mile, and u for US survey foot. By
   default we compute such distances using a spherical approximation  with
   great  circles.  Prepend - to a distance (or the unit is no distance is
   given) to perform "Flat Earth" calculations (quicker but less accurate)
   or  prepend  +  to perform exact geodesic calculations (slower but more
   accurate).

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. (more ...)

GEOGRAPHICAL AND TIME COORDINATES

   When the output grid type is netCDF, the coordinates  will  be  labeled
   "longitude", "latitude", or "time" based on the attributes of the input
   data or grid (if any) or on the -f or -R  options.  For  example,  both
   -f0x  -f1t  and  -R90w/90e/0t/3t  will result in a longitude/time grid.
   When the x, y, or z coordinate is time, it will be stored in  the  grid
   as  relative  time since epoch as specified by TIME_UNIT and TIME_EPOCH
   in the gmt.conf file or on the command  line.  In  addition,  the  unit
   attribute of the time variable will indicate both this unit and epoch.

EXAMPLES

   Suppose  you  have  used  surface  to  grid  ship gravity in the region
   between 148E - 162E and 8N - 32N, and you do  not  trust  the  gridding
   near  the  edges, so you want to keep only the area between 150E - 160E
   and 10N - 30N, then:

          gmt grdcut grav_148_162_8_32.nc -Ggrav_150_160_10_30.nc -R150/160/10/30 -V

   To return the subregion of a grid such that any boundary  strips  where
   all values are entirely above 0 are excluded, try

          gmt grdcut bathy.nc -Gtrimmed_bathy.nc -Z-/0 -V

   To  return  the  subregion  of  a grid that contains all nodes within a
   distance of 500 km from the point 45,30 try

          gmt grdcut bathy.nc -Gsubset_bathy.nc -S45/30/500k -V

COPYRIGHT

   2016, P. Wessel, W. H. F. Smith, R. Scharroo, J. Luis, and F. Wobbe

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