## NAME

          psmask - To clip or mask areas of no data on a map

## SYNOPSIS

          psmask [xyzfile] -Idx[m|c][/dy[m|c]] -Jparameters
          -Rwest/east/south/north[r] [ -Btickinfo ] [ -Ddumpfile ] [
          -Eazimuth/elevation ] [ -F ] [ -Gr/g/b ] [ -H[nrec] ] [ -K ] [ -M[flag]
          ] [ -N ] [ -O ] [ -P ] [ -Sradius[k] ] [ -T ] [ -U[/dx/dy/][label] ] [
          -V ] [ -Xx-shift ] [ -Yy-shift ] [ -ccopies ]  [ -: ] [ -bi[s][n] ]

          psmask -C [ -K ] [ -O ]

## DESCRIPTION

          psmask reads a (x,y,z) file [or standard input] and uses this
          information to find out which grid cells are reliable.  Only gridcells
          which have one or more data points are considered reliable.  As an
          option, you may specify a radius of influence. Then, all gridcells
          that are within radius of a data point are considered reliable.
          Furthermore, an option is provided to reverse the sense of the test.
          Having found the reliable/not reliable points, psmask will either
          paint tiles to mask these nodes (with the -T) switch, or use
          contouring to create polygons that will clip out regions of no
          interest.  When clipping is initiated, it will stay in effect until
          turned off by a second call to psmask using the -C option.

          xyzfile
               File with (x,y,z) values (e.g., that was used to run surface).
               If no file is given, standard input is read.  For binary files,
               see -b.

          -I   x_inc [and optionally y_inc] is the grid spacing. Append m to
               indicate minutes or c to indicate seconds.

          -J   Selects the map projection. Scale is cm/degree, 1:xxxxx, or width
               in cm (upper case modifier).

               CYLINDRICAL PROJECTIONS:

               -Jclon0/lat0/scale (Cassini)
               -Jjlon0/scale (Miller)
               -Jmscale (Mercator - Greenwich and Equator as origin)
               -Jmlon0/lat0/scale (Mercator - Give meridian and standard
               parallel)
               -Joalon0/lat0/azimuth/scale (Oblique Mercator - point and
               azimuth)
               -Joblon0/lat0/lon1/lat1/scale (Oblique Mercator - two points)
               -Joclon0/lat0/lonp/latp/scale (Oblique Mercator - point and pole)
               -Jqlon0/scale (Equidistant Cylindrical Projection (Plate Carree))
               -Jtlon0/scale (TM - Transverse Mercator, with Equator as y = 0)
               -Jtlon0/lat0/scale (TM - Transverse Mercator, set origin)
               -Juzone/scale (UTM - Universal Transverse Mercator)
               -Jylon0/lats/scale (Basic Cylindrical Projection)

               AZIMUTHAL PROJECTIONS:

               -Jalon0/lat0/scale (Lambert).
               -Jelon0/lat0/scale (Equidistant).
               -Jflon0/lat0/horizon/scale (Gnomonic).
               -Jglon0/lat0/scale (Orthographic).
               -Jslon0/lat0/scale (General Stereographic)

               CONIC PROJECTIONS:

               -Jblon0/lat0/lat1/lat2/scale (Albers)
               -Jdlon0/lat0/lat1/lat2/scale (Equidistant)
               -Jllon0/lat0/lat1/lat2/scale (Lambert)

               MISCELLANEOUS PROJECTIONS:

               -Jhlon0/scale (Hammer)
               -Jilon0/scale (Sinusoidal)
               -Jk[f|s]lon0/scale (Eckert IV (f) and VI (s))
               -Jnlon0/scale (Robinson)
               -Jrlon0/scale (Winkel Tripel)
               -Jvlon0/scale (Van der Grinten)
               -Jwlon0/scale (Mollweide)

               NON-GEOGRAPHICAL PROJECTIONS:

               -Jpscale (Linear projection for polar (theta,r) coordinates)
               -Jxx-scale[l|ppow][/y-scale[l|ppow]] (Linear, log, and power
               scaling)
               More details can be found in the psbasemap manpages.

          -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

          No space between the option flag and the associated arguments

          -B   Sets map boundary tickmark intervals. See psbasemap for details.

          -C   Mark end of existing clip path.  No input file is needed.
               Implicitly sets -O.

          -D   Dumps out the resulting clipping polygons to disk.  Ignored if -T
               is set.  If no dumpprefix is given we use mask (Files will be
               called mask_*.d).

          -E   Sets the viewpoint's azimuth and elevation for perspective plots
               [180/90]

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

          -G   Paint the clip polygons [or tiles] with gray-shade or color
               [Default is no fill].  Specify the shade (0-255) or color (r/g/b,
               each in 0-255).

          -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.  Not used with binary data.

          -K   More PostScript code will be appended later [Default terminates
               the plot system].

          -M   Multiple segment file(s).  Segments are separated by a special
               record.  For ASCII files the first character must be flag
               [Default is '>'].  For binary files all fields must be NaN.

          -N   Invert the sense of the test, i.e. clip regions where there is
               data coverage.

          -O   Selects Overlay plot mode [Default initializes a new plot
               system].

          -P   Selects Portrait plotting mode [GMT Default is Landscape, see
               gmtdefaults to change this].

          -S   Sets radius of influence. Grid nodes within radius of a data
               point are considered reliable. [Default is 0, which means that
               only grid cells with data in them are reliable].  Append k to
               indicated km, also implying that -R -I are in degrees.

          -T   Plot tiles instead of clip polygons (Only works with -Jx, -Jj,
               -Jm, -Jq, and -Jy).

          -U   Draw Unix System time stamp on plot.  User may specify where the
               lower left corner of the stamp should fall on the page relative
               to lower left corner of plot in cm [Default is (-2c/-2c)].
               Optionally, append a label, or c (which will plot the command
               string.)

          -V   Selects verbose mode, which will send progress reports to stderr
               [Default runs "silently"].

          -X -Y
               Shift origin of plot by (x-shift,y-shift) cm  [Default is
               (a2.5c,a2.5c) for new plots, (0,0) for overlays].  Prepend a for
               absolute coordinates; the default (r) will reset plot origin.

          -:   Toggles between (longitude,latitude) and (latitude,longitude)
               input/output.  [Default is (longitude,latitude)].

          -c   Specifies the number of plot copies. [Default is 1]

          -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 make an overlay PostScript file that will mask out the regions of a
          contour map where there is no control data using clip polygons, try:

          psmask africa_grav.xyg -R20/40/20/40 -I5m -JM10i -O -K > mask.ps

          The same example but this time we use tiling:

          psmask africa_grav.xyg -R20/40/20/40 -I5m -JM10i -T -O -K > mask.ps

## SEE ALSO

          gmt, grdmask, surface, psbasemap, psclip