NAME

      triangulate - Perform optimal Delauney triangulation and gridding

SYNOPSIS

      triangulate infiles [ -Dx|y ] [ -Eempty ] [ -Ggrdfile ] [ -H[nrec] ] [
      -Ix_inc[m|c][/y_inc[m|c]] ] [ -Jparameters ] [ -M[flag] ] [
      -Rwest/east/south/north[r] ] [ -V ] [ -Z ] [ -: ] [ -bi[s][n] ] [
      -bo[s] ]

DESCRIPTION

      triangulate reads one or more ASCII [or binary] files (or standard
      input) containing x,y[,z] and performs Delauney triangulation, i.e.,
      it find how the points should be connected to give the most
      equilateral triangulation possible.  If a map projection is chosen
      then it is applied before the triangulation is calculated.  By
      default, the output is triplets of point id numbers that make up each
      triangle and is written to standard output.  The id numbers refer to
      the points position in the input file.  As an option, you may choose
      to create a multiple segment file that can be piped through psxy to
      draw the triangulation network.  If -G -I are set a grid will be
      calculated based on the surface defined by the planar triangles.  The
      actual algorithm used in the triangulations is either that of
      Shewchuck [1996] or Watson [1982].  This choice is made during the GMT
      installation.

      infiles
           Data files with the point coordinates in ASCII (or binary; see
           -b).  If no files are given the standard input is read.

OPTIONS

      -D   Take either the x- or y-derivatives of surface represented by the
           planar facets (only used when -G is set).

      -E   Set the value assigned to empty nodes when -G is set [NaN].

      -G   Use triangulation to grid the data onto an even grid (specified
           with -I, -R).  Append the name of the output grid file.  The
           interpolation is performed in the original coordinates, so if
           your triangles are close to the poles you are better off
           projecting all data to a local coordinate system before using
           triangulate (this is true of all gridding routines).

      -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.

      -I   x_inc [and optionally y_inc] sets the grid  size for optional
           grid output (see -G).  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.

      -M   Output triangulation network as multiple line segments separated
           by a record whose first character is flag [>].  To plot, use psxy
           with the -M option (see Examples).

      -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.

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

      -Z   Controls whether binary data file has two or three columns [2].
           Ignored if -b is not set.

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

      -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].

      -bo  Selects binary output.  Append s for single precision [Default is
           double].  Node ids are stored as binary 4-byte integer triplets.
           -bo is ignored if -M is selected.

EXAMPLES

      To triangulate the points in the file samples.xyz, store the triangle
      information in a binary file, and make a grid for the given area and
      spacing, try

      triangulate samples.xyz -bo -R0/30/0/30 -I2 -Gsurf.grd > samples.ijk

      To draw the optimal Delauney triangulation network based on the same
      file using a 6-inch-wide Mercator map, try

      triangulate samples.xyz -M -R-100/-90/30/34 -JM6i | psxy -M -R-100/-
      90/30/34 -JM6i -W0.5p -B1 > network.ps

SEE ALSO

      gmt, pscontour

REFERENCES

      Watson, D. F., 1982, Acord: Automatic contouring of raw data, Comp. &
      Geosci., 8, 97-101.
      Shewchuck, J. R., 1996, Triangle: Engineering a 2D Quality Mesh
      Generator and Delaunay Triangulator, First Workshop on Applied
      Computational Geometry (Philadelphia, PA), 124-133, ACM, May 1996.
      www.cs.cmu.edu/~quake/triangle.html