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 inch/degree, 1:xxxxx, or
           width in inch (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)
           -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)
           -Jllon0/lat0/lat1/lat2/scale (Lambert)

           MISCELLANEOUS PROJECTIONS:

           -Jhlon0/scale (Hammer)
           -Jilon0/scale (Sinusoidal)
           -Jklon0/scale (Eckert VI)
           -Jnlon0/scale (Robinson)
           -Jrlon0/scale (Winkel Tripel)
           -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 inch [Default is (-0.75i/-
           0.75i)].  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) inch  [Default is
           (a1i,a1i) 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