GRDMASK(l)																GRDMASK(l)

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 depend-
       ing 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)