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] [ -A ] [ -F ] [ -H[nrec] ] [ -L ] [ -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  poly-
       gon 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".

       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

       -A     If the input data are geographic (as indicated by -L)  then  the
              sides in the polygons will be approximated by great circle arcs.
              This can be turned off using the -A switch.

       -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.

       -L     Indicates that the x column contains longitudes, which may  dif-
              fer  from  the  regions  in  -R  by  [multiples  of] 360 degrees
              [Default assumes no periodicity].

       -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)



GMT3.4.6                          1 Jan 2005                        GRDMASK(l)

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