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] ] [  -M[flag]  ]  [
       -Nout/edge/in  ]  [  -S[radius][k]  ]  [  -V  ]  [ -: ] [ -bi[s][n] ] [
       -f[i|o]colinfo ]

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     xmin, xmax, ymin, and ymax specify the Region of  interest.  For
              geographic  regions,  these  limits  correspond  to  west, east,
              south, and north and you may specify them in decimal degrees  or
              in  [+-]dd:mm[:ss.xxx][W|E|S|N]  format.  Append r if lower left
              and upper right map coordinates are given instead of  wesn.  The
              two  shorthands  -Rg  -Rd  stand  for  global  domain  (0/360 or
              -180/+180 in longitude respectively, with -90/+90 in  latitude).
              For  calendar time coordinates you may either give relative time
              (relative  to  the  selected  TIME_EPOCH  and  in  the  selected
              TIME_UNIT;  append  t  to  -JX|x),  or absolute time of the form
              [date]T[clock] (append T to -JX|x). At least  one  of  date  and
              clock must be present; the T is always required. The date string
              must be of the form [-]yyyy[-mm[-dd]]  (Gregorian  calendar)  or
              yyyy[-Www[-d]]  (ISO week calendar), while the clock string must
              be of the form hh:mm:ss[.xxx]. The use of delimiters  and  their
              type  and  positions must be as indicated (however, input/output
              and plotting formats are flexible).

OPTIONS

       -A     If the input data are geographic (as indicated by -fi) 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  .gmtdefaults4 file. If used, GMT
              default is 1 header record. Use -Hi if only  input  data  should
              have  header  records  [Default will write out header records if
              the input data have them].

       -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 and -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].

       -f     Special  formatting  of  input  and output columns (time or geo-
              graphical data) Specify i(nput) or  o(utput)  [Default  is  both
              input  and output].  Give one or more columns (or column ranges)
              separated by commas.  Append T (Absolute calendar time), t (time
              relative  to  chosen TIME_EPOCH), x (longitude), y (latitude), g
              (geographic coordinate), or f (floating point) to each column or
              column range item.

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)



GMT4.0                            1 Oct 2004                        GRDMASK(l)