1TRIANGULATE(1) GMT TRIANGULATE(1)
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6 triangulate - Do optimal (Delaunay) triangulation and gridding of
7 Cartesian table data [method]
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10 triangulate [ table ] [ -Cslpfile ] [ -Dx|y ] [ -Eempty ] [ -Ggrd‐
11 file ] [ -Iincrement ] [ -Jparameters ] [ -M ] [ -N ] [ -Q[n] ] [
12 -Rregion ] [ -S ] [ -V[level] ] [ -Z ] [ -bbinary ] [ -dnodata ] [
13 -eregexp ] [ -fflags ] [ -hheaders ] [ -iflags ] [ -r ] [ -:[i|o] ]
14 Note: No space is allowed between the option flag and the associated
16 arguments.
17
19 triangulate reads one or more ASCII [or binary] files (or standard
20 input) containing x,y[,z] and performs Delaunay triangulation, i.e., it
21 find how the points should be connected to give the most equilateral
22 triangulation possible. If a map projection (give -R and -J) is chosen
23 then it is applied before the triangulation is calculated. By default,
24 the output is triplets of point id numbers that make up each triangle
25 and is written to standard output. The id numbers refer to the points
26 position (line number, starting at 0 for the first line) in the input
27 file. As an option, you may choose to create a multiple segment file
28 that can be piped through psxy to draw the triangulation network. If -G
29 -I are set a grid will be calculated based on the surface defined by
30 the planar triangles. The actual algorithm used in the triangulations
31 is either that of Watson [1982] [Default] or Shewchuk [1996] (if
32 installed; type triangulate - to see which method is selected). This
33 choice is made during the GMT installation. Furthermore, if the
34 Shewchuk algorithm is installed then you can also perform the calcula‐
35 tion of Voronoi polygons and optionally grid your data via the natural
36 nearest neighbor algorithm.
37
39 None.
40
42 table One or more ASCII (or binary, see -bi[ncols][type]) data table
43 file(s) holding a number of data columns. If no tables are given
44 then we read from standard input.
45 -Cslpfile
47 Read a slope grid (in radians) and compute the propagated uncer‐
49 tainty in the
50 bathymetry using the CURVE algorithm [Zambo et al, 20xx].
51 Requires the -G option to specify the output grid. Note
52 that the slpgrid sets the domain for the output grid so
53 -R, -I, [-r] are not required. Cannot be used in con‐
54 junction with -D, -F, -M, -N, -Q, -S and -T.
55 -Dx|y Take either the x- or y-derivatives of surface represented by
57 the planar facets (only used when -G is set).
58 -Eempty
60 Set the value assigned to empty nodes when -G is set [NaN].
61 -Ggrdfile
63 Use triangulation to grid the data onto an even grid (specified
64 with -R -I). Append the name of the output grid file. The inter‐
65 polation is performed in the original coordinates, so if your
66 triangles are close to the poles you are better off projecting
67 all data to a local coordinate system before using triangulate
68 (this is true of all gridding routines) or instead select sph‐
69 triangulate. For natural nearest neighbor gridding you must add
70 -Qn.
71 -Ixinc[unit][+e|n][/yinc[unit][+e|n]]
73 x_inc [and optionally y_inc] is the grid spacing. Optionally,
74 append a suffix modifier. Geographical (degrees) coordinates:
75 Append m to indicate arc minutes or s to indicate arc seconds.
76 If one of the units e, f, k, M, n or u is appended instead, the
77 increment is assumed to be given in meter, foot, km, Mile, nau‐
78 tical mile or US survey foot, respectively, and will be con‐
79 verted to the equivalent degrees longitude at the middle lati‐
80 tude of the region (the conversion depends on PROJ_ELLIPSOID).
81 If y_inc is given but set to 0 it will be reset equal to x_inc;
82 otherwise it will be converted to degrees latitude. All coordi‐
83 nates: If +e is appended then the corresponding max x (east) or
84 y (north) may be slightly adjusted to fit exactly the given
85 increment [by default the increment may be adjusted slightly to
86 fit the given domain]. Finally, instead of giving an increment
87 you may specify the number of nodes desired by appending +n to
88 the supplied integer argument; the increment is then recalcu‐
89 lated from the number of nodes and the domain. The resulting
90 increment value depends on whether you have selected a grid‐
91 line-registered or pixel-registered grid; see App-file-formats
92 for details. Note: if -Rgrdfile is used then the grid spacing
93 has already been initialized; use -I to override the values.
94 -Jparameters (more ...)
96 Select map projection.
97 -M Output triangulation network as multiple line segments separated
99 by a segment header record.
100 -N Used in conjunction with -G to also write the triplets of the
102 ids of all the Delaunay vertices [Default only writes the grid].
103 -Q[n] Output the edges of the Voronoi cells instead [Default is Delau‐
105 nay triangle edges]. Requires -R and is only available if linked
106 with the Shewchuk [1996] library. Note that -Z is ignored on
107 output. Optionally, append n for combining the edges into closed
108 Voronoi polygons.
109 -Rxmin/xmax/ymin/ymax[+r][+uunit] (more ...)
111 Specify the region of interest.
112 -S Output triangles as polygon segments separated by a segment
114 header record. Requires Delaunay triangulation.
115 -T Output edges or polygons even if gridding has been selected with
117 the -G option [Default will not output the triangulation or
118 Voronoi polygons is gridding is selected].
119 -V[level] (more ...)
121 Select verbosity level [c].
122 -Z Controls whether we read (x,y) or (x,y,z) data and if z should
124 be output when -M or -S are used [Read (x,y) only].
125 -bi[ncols][t] (more ...)
127 Select native binary input. [Default is 2 input columns].
128 -bo[ncols][type] (more ...)
130 Select native binary output. [Default is same as input]. Node
131 ids are stored as double triplets.
132 -d[i|o]nodata (more ...)
134 Replace input columns that equal nodata with NaN and do the
135 reverse on output.
136 -e[~]"pattern" | -e[~]/regexp/[i] (more ...)
138 Only accept data records that match the given pattern.
139 -f[i|o]colinfo (more ...)
141 Specify data types of input and/or output columns.
142 -h[i|o][n][+c][+d][+rremark][+rtitle] (more ...)
144 Skip or produce header record(s).
145 -icols[+l][+sscale][+ooffset][,...] (more ...)
147 Select input columns and transformations (0 is first column).
148 -r (more ...)
150 Set pixel node registration [gridline]. (Only valid with -G).
151 -:[i|o] (more ...)
153 Swap 1st and 2nd column on input and/or output.
154 -^ or just -
156 Print a short message about the syntax of the command, then
157 exits (NOTE: on Windows just use -).
158 -+ or just +
160 Print an extensive usage (help) message, including the explana‐
161 tion of any module-specific option (but not the GMT common
162 options), then exits.
163 -? or no arguments
165 Print a complete usage (help) message, including the explanation
166 of all options, then exits.
167
169 The ASCII output formats of numerical data are controlled by parameters
170 in your gmt.conf file. Longitude and latitude are formatted according
171 to FORMAT_GEO_OUT, absolute time is under the control of FOR‐
172 MAT_DATE_OUT and FORMAT_CLOCK_OUT, whereas general floating point val‐
173 ues are formatted according to FORMAT_FLOAT_OUT. Be aware that the for‐
174 mat in effect can lead to loss of precision in ASCII output, which can
175 lead to various problems downstream. If you find the output is not
176 written with enough precision, consider switching to binary output (-bo
177 if available) or specify more decimals using the FORMAT_FLOAT_OUT set‐
178 ting.
179
181 Regardless of the precision of the input data, GMT programs that create
182 grid files will internally hold the grids in 4-byte floating point
183 arrays. This is done to conserve memory and furthermore most if not all
184 real data can be stored using 4-byte floating point values. Data with
185 higher precision (i.e., double precision values) will lose that preci‐
186 sion once GMT operates on the grid or writes out new grids. To limit
187 loss of precision when processing data you should always consider nor‐
188 malizing the data prior to processing.
189
191 To triangulate the points in the file samples.xyz, store the triangle
192 information in a binary file, and make a grid for the given area and
193 spacing, use
194 gmt triangulate samples.xyz -bo -R0/30/0/30 -I2 -Gsurf.nc > samples.ijk
196 To draw the optimal Delaunay triangulation network based on the same
198 file using a 15-cm-wide Mercator map, use
199 gmt triangulate samples.xyz -M -R-100/-90/30/34 -JM15c | gmt psxy \
201 -R-100/-90/30/34 -JM15c -W0.5p -B1 > network.ps
202 To instead plot the Voronoi cell outlines, try
204 gmt triangulate samples.xyz -M -Q -R-100/-90/30/34 -JM15c | \
206 gmt psxy -R-100/-90/30/34 -JM15c -W0.5p -B1 > cells.ps
207 To combine the Voronoi outlines into polygons and paint them according
209 to their ID, try
210 gmt triangulate samples.xyz -M -Qn -R-100/-90/30/34 -JM15c | \
212 gmt psxy -R-100/-90/30/34 -JM15c -W0.5p+cf -L -B1 -Ccolors.cpt -L > polygons.ps
213 To grid the data using the natural nearest neighbor algorithm, try
215 gmt triangulate samples.xyz -Gnnn.nc -Qn -R-100/-90/30/34 -I0.5
217
219 The uncertainty propagation for bathymetric grids requires both hori‐
220 zontal and vertical uncertainties and these are weighted given the
221 local slope. See the references for more details.
222
224 gmt, greenspline, nearneighbor, pscontour, sphdistance, sphinterpolate,
225 sphtriangulate, surface
226
228 Watson, D. F., 1982, Acord: Automatic contouring of raw data, Comp. &
229 Geosci., 8, 97-101.
230 Shewchuk, J. R., 1996, Triangle: Engineering a 2D Quality Mesh Genera‐
232 tor and Delaunay Triangulator, First Workshop on Applied Computational
233 Geometry (Philadelphia, PA), 124-133, ACM, May 1996.
234 Shewchuk's Homepage
236
238 2019, P. Wessel, W. H. F. Smith, R. Scharroo, J. Luis, and F. Wobbe
2395.4.5 Feb 24, 2019 TRIANGULATE(1)