sphtriangulate(1) GMT sphtriangulate(1)
NAME
sphtriangulate - Delaunay or Voronoi construction of spherical lon,lat
data
SYNOPSIS
sphtriangulate [ table ] [ -A ] [ -C ] [ -D ] [ -Lunit ] [ -Nnfile
] [ -Qd|v ] [ -T ] [ -V[level] ] [ -bbinary ] [ -dnodata ] [ -ereg-
exp ] [ -hheaders ] [ -iflags ] [ -:[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 triangula-
tion, i.e., it determines 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
closed 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.
REQUIRED ARGUMENTS
None.
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 out-
put 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 coordi-
nates (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 approxima-
tion is used unless PROJ_ELLIPSOID is set to an actual ellip-
soid, 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 fill-
able triangles or polygons]. When used with -A we store arc
length in the segment header in chosen unit (see -L).
-V[level] (more a|)
Select verbosity level [c].
-bi[ncols][t] (more a|)
Select native binary input. [Default is 2 input columns].
-bo[ncols][type] (more a|)
Select native binary output. [Default is same as input].
-d[i|o]nodata (more a|)
Replace input columns that equal nodata with NaN and do the
reverse on output.
-e[~]^<i>apattern^<i>a | -e[~]/regexp/[i] (more a|)
Only accept data records that match the given pattern.
-h[i|o][n][+c][+d][+rremark][+rtitle] (more a|)
Skip or produce header record(s).
-:[i|o] (more a|)
Swap 1st and 2nd column on input and/or output.
-r (more a|)
Set pixel node registration [gridline].
-^ or just -
Print a short message about the syntax of the command, then
exits (NOTE: on Windows just use -).
-+ or just +
Print an extensive usage (help) message, including the explana-
tion 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 all options, then exits.
ASCII FORMAT PRECISION
The ASCII output formats of numerical data are controlled by parameters
in your gmt.conf file. Longitude and latitude are formatted according
to FORMAT_GEO_OUT, absolute time is under the control of FOR-
MAT_DATE_OUT and FORMAT_CLOCK_OUT, whereas general floating point val-
ues are formatted according to FORMAT_FLOAT_OUT. Be aware that the for-
mat in effect can lead to loss of precision in ASCII output, which can
lead to various problems downstream. If you find the output is not
written with enough precision, consider switching to binary output (-bo
if available) or specify more decimals using the FORMAT_FLOAT_OUT set-
ting.
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 -Bag | gv -
To compute the optimal Delaunay triangulation network based on the mul-
tiple 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
SEE ALSO
gmt(1), triangulate(1), sphdistance(1)
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.
COPYRIGHT
2017, P. Wessel, W. H. F. Smith, R. Scharroo, J. Luis, and F. Wobbe
5.4.2 Jun 24, 2017 sphtriangulate(1)
gmt5 5.4.2 - Generated Thu Jun 29 16:33:17 CDT 2017