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 writ-
ten 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 seg-
ment file that can be piped through psxy to draw the triangulation net-
work. 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 tri-
angulations is either that of Watson [1982] [Default] or Shewchuck
[1996] (if installed). This choice is made during the GMT installa-
tion.
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 pro-
jecting all data to a local coordinate system before using tri-
angulate (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 Car-
ree))
-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 dif-
fer 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].
-O Selects Overlay plot mode [Default initializes a new plot sys-
tem]. 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(l), pscontour(l)
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 Genera-
tor and Delaunay Triangulator, First Workshop on Applied Computational
Geometry (Philadelphia, PA), 124-133, ACM, May 1996.
www.cs.cmu.edu/~quake/triangle.html
GMT3.4.6 1 Jan 2005 TRIANGULATE(l)
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