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 ] [ -L ] [ -M[flag] ] [ -Rwest/east/south/north[r] ] [ -V ] [ -Z ] [ -: ] [  -bi[s][n]  ]  [
       -bo[s][n] ]

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  Watson  [1982]
       [Default] or Shewchuck [1996] (if installed).  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 UNIT/degree, 1:xxxxx, or width in UNIT (upper case modifier).
              UNIT  is  cm,  inch,  or m, depending on the MEASURE_UNIT setting in .gmtdefaults, but this can be
              overridden on the command line by appending the c, i, or m to the scale/width value.

              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/[slat/]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:

              -Jp[a]scale[/origin] (polar (theta,r) coordinates, optional a for azimuths and offset theta [0])
              -Jxx-scale[l|ppow][/y-scale[l|ppow]] (Linear, log, and power scaling)
              More details can be found in the psbasemap manpages.

       -L     Indicates that the x column contains longitudes, which  may  differ  from  the  region  in  -R  by
              [multiples of] 360 degrees [Default assumes no periodicity].

       -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)].  Applies to geographic coordinates only.

       -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  15  -cm-wide  Mercator
       map, try

       triangulate  samples.xyz  -M  -R-100/-90/30/34  -JM15c  |  psxy  -M  -R-100/-90/30/34 -JM15c -W0.5p -B1 >
       network.ps

SEE ALSO

       gmt(1gmt), pscontour(1gmt)

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

                                                   1 Jan 2004                                     TRIANGULATE(l)