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][n] ] [ -f[i|o]colinfo ]
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 Shewchuk
[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 .gmtdefaults4 file. If used, GMT
default is 1 header record. Use -Hi if only input data should
have header records [Default will write out header records if
the input data have them].
-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 .gmtdefaults4, but this
can be overridden on the command line by appending c, i, or m to
the scale/width value. For map height, max dimension, or min
dimension, append h, +, or - to the width, respectively.
CYLINDRICAL PROJECTIONS:
-Jclon0/lat0/scale (Cassini)
-Jjlon0/scale (Miller)
-Jmscale (Mercator - Greenwich and Equator as origin)
-Jmlon0/lat0/scale (Mercator - Give meridian and standard paral-
lel)
-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]][d] (Linear, log, and power
scaling)
More details can be found in the psbasemap man pages.
-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 xmin, xmax, ymin, and ymax specify the Region of interest. For
geographic regions, these limits correspond to west, east,
south, and north and you may specify them in decimal degrees or
in [+-]dd:mm[:ss.xxx][W|E|S|N] format. Append r if lower left
and upper right map coordinates are given instead of wesn. The
two shorthands -Rg -Rd stand for global domain (0/360 or
-180/+180 in longitude respectively, with -90/+90 in latitude).
For calendar time coordinates you may either give relative time
(relative to the selected TIME_EPOCH and in the selected
TIME_UNIT; append t to -JX|x), or absolute time of the form
[date]T[clock] (append T to -JX|x). At least one of date and
clock must be present; the T is always required. The date string
must be of the form [-]yyyy[-mm[-dd]] (Gregorian calendar) or
yyyy[-Www[-d]] (ISO week calendar), while the clock string must
be of the form hh:mm:ss[.xxx]. The use of delimiters and their
type and positions must be as indicated (however, input/output
and plotting formats are flexible).
-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 and/or output. [Default is (longitude,latitude)]. Append
i to select input only or o to select output only. [Default
affects both].
-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]. Append n for the number of columns in the binary
file(s).
Node ids are stored as binary 4-byte integer triplets. -bo is
ignored if -M is selected.
-f Special formatting of input and output columns (time or geo-
graphical data) Specify i(nput) or o(utput) [Default is both
input and output]. Give one or more columns (or column ranges)
separated by commas. Append T (Absolute calendar time), t (time
relative to chosen TIME_EPOCH), x (longitude), y (latitude), g
(geographic coordinate), or f (floating point) to each column or
column range item.
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, use
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, use
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.
Shewchuk, 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
GMT4.0 1 Oct 2004 TRIANGULATE(l)
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