1SPHTRIANGULATE(1) GMT SPHTRIANGULATE(1)
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6 sphtriangulate - Delaunay or Voronoi construction of spherical lon,lat
7 data
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10 sphtriangulate [ table ] [ -A ] [ -C ] [ -D ] [ -Lunit ] [ -Nnfile
11 ] [ -Qd|v ] [ -T ] [ -V[level] ] [ -bbinary ] [ -dnodata ] [ -ereg‐
12 exp ] [ -hheaders ] [ -iflags ] [ -:[i|o] ]
13 Note: No space is allowed between the option flag and the associated
15 arguments.
16
18 sphtriangulate reads one or more ASCII [or binary] files (or standard
19 input) containing lon, lat and performs a spherical Delaunay triangula‐
20 tion, i.e., it determines how the points should be connected to give
21 the most equilateral triangulation possible on the sphere. Optionally,
22 you may choose -Qv which will do further processing to obtain the
23 Voronoi polygons. Normally, either set of polygons will be written as
24 closed fillable segment output; use -T to write unique arcs instead. As
25 an option, compute the area of each triangle or polygon. The algorithm
26 used is STRIPACK.
27
29 None.
30
32 table One or more ASCII (or binary, see -bi[ncols][type]) data table
33 file(s) holding a number of data columns. If no tables are given
34 then we read from standard input.
35 -A Compute the area of the spherical triangles (-Qd) or polygons
37 (-Qv) and write the areas (in chosen units; see -L) in the out‐
38 put segment headers [no areas calculated].
39 -C For large data set you can save some memory (at the expense of
41 more processing) by only storing one form of location coordi‐
42 nates (geographic or Cartesian 3-D vectors) at any given time,
43 translating from one form to the other when necessary [Default
44 keeps both arrays in memory].
45 -D Used to skip the last (repeated) input vertex at the end of a
47 closed segment if it equals the first point in the segment.
48 [Default uses all points].
49 -Lunit Specify the unit used for distance and area calculations. Choose
51 among e (m), f (foot), k (km), m (mile), n (nautical mile), u
52 (survey foot), or d (spherical degree). A spherical approxima‐
53 tion is used unless PROJ_ELLIPSOID is set to an actual ellip‐
54 soid, in which case we convert latitudes to authalic latitudes
55 before calculating areas. When degree is selected the areas are
56 given in steradians.
57 -Nnfile
59 Write the information pertaining to each polygon. For Delaunay:
60 the three node number and the triangle area (if -A was set); for
61 Voronoi the unique node lon, lat and polygon area (if -A was
62 set)) to a separate file. This information is also encoded in
63 the segment headers of ASCII output files. Required if binary
64 output is needed.
65 -Qd|v Append d for Delaunay triangles or v for Voronoi polygons
67 [Delaunay]. If -bo is used then -N may be used to specify a
68 separate file where the polygon information normally is written.
69 -T Write the unique arcs of the construction [Default writes fill‐
71 able triangles or polygons]. When used with -A we store arc
72 length in the segment header in chosen unit (see -L).
73 -V[level] (more ...)
75 Select verbosity level [c].
76 -bi[ncols][t] (more ...)
78 Select native binary input. [Default is 2 input columns].
79 -bo[ncols][type] (more ...)
81 Select native binary output. [Default is same as input].
82 -d[i|o]nodata (more ...)
84 Replace input columns that equal nodata with NaN and do the
85 reverse on output.
86 -e[~]"pattern" | -e[~]/regexp/[i] (more ...)
88 Only accept data records that match the given pattern.
89 -h[i|o][n][+c][+d][+rremark][+rtitle] (more ...)
91 Skip or produce header record(s).
92 -:[i|o] (more ...)
94 Swap 1st and 2nd column on input and/or output.
95 -r (more ...)
97 Set pixel node registration [gridline].
98 -^ or just -
100 Print a short message about the syntax of the command, then
101 exits (NOTE: on Windows just use -).
102 -+ or just +
104 Print an extensive usage (help) message, including the explana‐
105 tion of any module-specific option (but not the GMT common
106 options), then exits.
107 -? or no arguments
109 Print a complete usage (help) message, including the explanation
110 of all options, then exits.
111
113 The ASCII output formats of numerical data are controlled by parameters
114 in your gmt.conf file. Longitude and latitude are formatted according
115 to FORMAT_GEO_OUT, absolute time is under the control of FOR‐
116 MAT_DATE_OUT and FORMAT_CLOCK_OUT, whereas general floating point val‐
117 ues are formatted according to FORMAT_FLOAT_OUT. Be aware that the for‐
118 mat in effect can lead to loss of precision in ASCII output, which can
119 lead to various problems downstream. If you find the output is not
120 written with enough precision, consider switching to binary output (-bo
121 if available) or specify more decimals using the FORMAT_FLOAT_OUT set‐
122 ting.
123
125 To triangulate the points in the file testdata.txt, and make a Voronoi
126 diagram via psxy, use
127 gmt sphtriangulate testdata.txt -Qv | psxy -Rg -JG30/30/6i -L -P -W1p -Bag | gv -
129 To compute the optimal Delaunay triangulation network based on the mul‐
131 tiple segment file globalnodes.d and save the area of each triangle in
132 the header record, try
133 gmt sphtriangulate globalnodes.d -Qd -A > global_tri.d
135
137 gmt, triangulate, sphdistance
138
140 Renka, R, J., 1997, Algorithm 772: STRIPACK: Delaunay Triangulation and
141 Voronoi Diagram on the Surface of a Sphere, AMC Trans. Math. Software,
142 23(3), 416-434.
143
145 2019, P. Wessel, W. H. F. Smith, R. Scharroo, J. Luis, and F. Wobbe
1465.4.5 Feb 24, 2019 SPHTRIANGULATE(1)