NAME

     grdmask - Create mask grdfiles from xy paths.


SYNOPSIS

     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] ]


DESCRIPTION

     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 dis-
     tance from the nearest data point.  If the  distance  speci-
     fied is zero then only the nodes nearest each data point are
     considered "inside".

     pathfiles
          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.


OPTIONS

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

     -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].


EXAMPLES

     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  -V

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

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


SEE ALSO

     gmt(l), grdlandmask(l), grdmath(l),  grdclip(l),  psmask(l),
     psclip(l)