sphtriangulate
sphtriangulate - Delaunay or Voronoi construction of spherical lon,lat data
Synopsis
sphtriangulate [ table ] [ -A ] [ -C ] [ -D ]
[ -Lunit ] [ -Nnfile ] [ -Qd|v ]
[ -T ] [ -V[level] ]
[ -b<binary> ]
[ -d<nodata> ]
[ -h<headers> ]
[ -i<flags> ]
[ -:[i|o] ]
Note: No space is allowed between the option flag and the associated arguments.
Description
sphtriangulate reads one or more ASCII [or binary] files (or
standard input) containing lon, lat and performs a spherical Delaunay
triangulation, i.e., it find how the points should be connected to give
the most equilateral triangulation possible on the sphere. Optionally,
you may choose -Qv which will do further processing to obtain the
Voronoi polygons. Normally, either set of polygons will be written as
fillable segment output; use -T to write unique arcs instead. As an
option, compute the area of each triangle or polygon. The algorithm used
is STRIPACK.
Optional Arguments
- table
- One or more ASCII (or binary, see -bi[ncols][type]) data
table file(s) holding a number of data columns. If no tables are given
then we read from standard input.
- -A
- Compute the area of the spherical triangles (-Qd) or polygons
(-Qv) and write the areas (in chosen units; see -L) in the
output segment headers [no areas calculated].
- -C
- For large data set you can save some memory (at the expense of more
processing) by only storing one form of location coordinates
(geographic or Cartesian 3-D vectors) at any given time, translating
from one form to the other when necessary [Default keeps both arrays in memory].
- -D
- Used to skip the last (repeated) input vertex at the end
of a closed segment if it equals the first point in the segment.
[Default uses all points].
- -Lunit
- Specify the unit used for distance and area calculations. Choose
among e (m), f (foot), k (km), m (mile), n
(nautical mile), u (survey foot), or d (spherical degree). A
spherical approximation is used unless PROJ_ELLIPSOID is set to
an actual ellipsoid, in which case we convert latitudes to authalic
latitudes before calculating areas. When degree is selected the
areas are given in steradians.
- -Nnfile
- Write the information pertaining to each polygon. For Delaunay: the
three node number and the triangle area (if -A was set); for
Voronoi the unique node lon, lat and polygon area (if -A was
set)) to a separate file. This information is also encoded in the
segment headers of ASCII output files. Required if binary output is needed.
- -Qd|v
- Append d for Delaunay triangles or v for Voronoi polygons [Delaunay].
If -bo is used then -N may be used to specify a separate file where the
polygon information normally is written.
- -T
- Write the unique arcs of the construction [Default writes fillable
triangles or polygons]. When used with -A we store arc length in
the segment header in chosen unit (see -L).
- -V[level] (more ...)
- Select verbosity level [c].
- -bi[ncols][t] (more ...)
- Select native binary input. [Default is 2 input columns].
- -bo[ncols][type] (more ...)
- Select native binary output. [Default is same as input].
- -d[i|o]nodata (more ...)
- Replace input columns that equal nodata with NaN and do the reverse on output.
- -h[i|o][n][+c][+d][+rremark][+rtitle] (more ...)
- Skip or produce header record(s).
- -:[i|o] (more ...)
- Swap 1st and 2nd column on input and/or output.
- -r (more ...)
- Set pixel node registration [gridline].
- -^ or just -
- Print a short message about the syntax of the command, then exits (NOTE: on Windows use just -).
- -+ or just +
- Print an extensive usage (help) message, including the explanation of
any module-specific option (but not the GMT common options), then exits.
- -? or no arguments
- Print a complete usage (help) message, including the explanation of
options, then exits.
- --version
- Print GMT version and exit.
- --show-datadir
- Print full path to GMT share directory and exit.
Examples
To triangulate the points in the file testdata.txt, and make a Voronoi
diagram via psxy, use
gmt sphtriangulate testdata.txt -Qv | psxy -Rg -JG30/30/6i -L -P -W1p -B0g30 | gv -
To compute the optimal Delaunay triangulation network based on the
multiple segment file globalnodes.d and save the area of each triangle
in the header record, try
gmt sphtriangulate globalnodes.d -Qd -A > global_tri.d
References
Renka, R, J., 1997, Algorithm 772: STRIPACK: Delaunay Triangulation and
Voronoi Diagram on the Surface of a Sphere, AMC Trans. Math. Software,
23(3), 416-434.