bionic (1) grdcut.1gmt.gz

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].

       -Rxmin/xmax/ymin/ymax[+r][+uunit] (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 just use -).

       -+ 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 all 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

SEE ALSO

       gmt, grdclip, grdinfo, grdpaste, surface

COPYRIGHT

       2018, P. Wessel, W. H. F. Smith, R. Scharroo, J. Luis, and F. Wobbe