grdmask - Create mask grdfiles from xy paths.


      grdmask pathfiles -Gmask_grd_file] -Ixinc[m|c][/yinc[m|c]]
      -Rwest/east/south/north[r] [ -F ] [ -H[nrec] ] [ -M[flag] ] [
      -Nout/edge/in ] [ -S[radius][k] ] [ -V ] [ -: ] [ -bi[s][n] ]


      grdmask can operate in 2 different modes. 1. It reads one or more xy-
      files that each define a closed polygon.  The nodes defined by the
      specified region and lattice spacing will be set equal to one of three
      possible values depending on whether the node is outside, on the
      polygon perimeter, or inside the polygon.  The resulting mask grdfile
      may be used in subsequent operations involving grdmath to mask out
      data from polygonal areas. 2. The xy-files simply represent data point
      locations and the mask is set to the inside or outside value depending
      on whether a node is within a maximum distance from the nearest data
      point.  If the distance specified is zero then only the nodes nearest
      each data point are considered "inside".

           The name of 1 or more ASCII [or binary, see -b] files holding the
           polygon(s) or data points.

      -G   Name of resulting output mask grd file.

      -I   x_inc [and optionally y_inc] is the grid spacing. Append m to
           indicate minutes or c to indicate seconds.

      -R   west, east, south, and north specify the Region of interest.  To
           specify boundaries in degrees and minutes [and seconds], use the
           dd:mm[:ss] format.  Append r if lower left and upper right map
           coordinates are given instead of wesn.


      -F   Force pixel registration.  [Default is grid registration].

      -H   Input file(s) has Header record(s).  Number of header records can
           be changed by editing your .gmtdefaults file.  If used, GMT
           default is 1 header record.

      -M   Multiple segment file.  Segments are separated by a record whose
           first character is flag.  [Default is '>'].

      -N   Sets the values that will be assigned to nodes that are outside
           the polygons, on the edge, or inside.  Values can be any number,
           including the textstring NaN  [Default is 0/0/1].

      -S   Set nodes depending on their distance from the nearest data
           point.  Nodes within radius [0] from a data point are considered
           inside.  Append k to indicate map units (e.g., -R -I in degrees
           and radius in km).

      -V   Selects verbose mode, which will send progress reports to stderr
           [Default runs "silently"].

      -bi  Selects binary input.  Append s for single precision [Default is
           double].  Append n for the number of columns in the binary
           file(s).  [Default is 2 input columns].


      To set all nodes inside and on the polygons coastline_*.xy to 0, and
      outside points to 1, do

      grdmask coastline_*.xy -R-60/-40/-40/-30 -I5m -N1/0/0 -Gland_mask.grd

      To set nodes within 50 km of data points to 1 and other nodes to NaN,

      grdmask -R-60/-40/-40/-30 -I5m -NNaN/1/1 -S50k
      -Gdata_mask.grd  -V


      gmt, grdlandmask, grdmath, grdclip, psmask, psclip

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