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 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".

       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  differ  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(1gmt), grdlandmask(1gmt), grdmath(1gmt), grdclip(1gmt), psmask(1gmt), psclip(1gmt)

                                                   1 Jan 2004                                         GRDMASK(l)