1TRIANGULATE(1) Generic Mapping Tools TRIANGULATE(1)
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6 triangulate - Perform optimal Delauney triangulation and gridding of
7 Cartesian data [method]
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10 triangulate infiles [ -Dx|y ] [ -Eempty ] [ -F ] [ -Ggrdfile ] [
11 -H[i][nrec] ] [ -Ixinc[unit][=|+][/yinc[unit][=|+]] ] [ -Jparameters ]
12 [ -M[i|o][flag] ] [ -Rwest/east/south/north[r] ] [ -V ] [ -Z ] [
13 -:[i|o] ] [ -b[i|o][s|S|d|D[ncol]|c[var1/...]] ] [ -f[i|o]colinfo ]
14
16 triangulate reads one or more ASCII [or binary] files (or standard
17 input) containing x,y[,z] and performs Delauney triangulation, i.e., it
18 find how the points should be connected to give the most equilateral
19 triangulation possible. If a map projection (give -R and -J) is chosen
20 then it is applied before the triangulation is calculated. By default,
21 the output is triplets of point id numbers that make up each triangle
22 and is written to standard output. The id numbers refer to the points
23 position (line number, starting at 0 for the first line) in the input
24 file. As an option, you may choose to create a multiple segment file
25 that can be piped through psxy to draw the triangulation network. If
26 -G -I are set a grid will be calculated based on the surface defined by
27 the planar triangles. The actual algorithm used in the triangulations
28 is either that of Watson [1982] [Default] or Shewchuk [1996] (if
29 installed; type triangulate - to see which method is selected). This
30 choice is made during the GMT installation.
31 infiles
33 Data files with the point coordinates in ASCII (or binary; see
34 -b). If no files are given the standard input is read.
35
37 -D Take either the x- or y-derivatives of surface represented by
38 the planar facets (only used when -G is set).
39 -E Set the value assigned to empty nodes when -G is set [NaN].
41 -F Force pixel node registration [Default is gridline registra‐
43 tion]. (Node registrations are defined in GMT Cookbook Appendix
44 B on grid file formats.) Only valid with -G).
45 -G Use triangulation to grid the data onto an even grid (specified
47 with -I, -R). Append the name of the output grid file. The
48 interpolation is performed in the original coordinates, so if
49 your triangles are close to the poles you are better off pro‐
50 jecting all data to a local coordinate system before using tri‐
51 angulate (this is true of all gridding routines).
52 -H Input file(s) has Header record(s). Number of header records
54 can be changed by editing your .gmtdefaults4 file. If used, GMT
55 default is 1 header record. Use -Hi if only input data should
56 have header records [Default will write out header records if
57 the input data have them]. Blank lines and lines starting with #
58 are always skipped.
59 -I x_inc [and optionally y_inc] sets the grid size for optional
61 grid output (see -G). Append m to indicate minutes or c to
62 indicate seconds.
63 -J Selects the map projection. Scale is UNIT/degree, 1:xxxxx, or
65 width in UNIT (upper case modifier). UNIT is cm, inch, or m,
66 depending on the MEASURE_UNIT setting in .gmtdefaults4, but this
67 can be overridden on the command line by appending c, i, or m to
68 the scale/width value. When central meridian is optional,
69 default is center of longitude range on -R option. Default
70 standard parallel is the equator. For map height, max dimen‐
71 sion, or min dimension, append h, +, or - to the width, respec‐
72 tively.
73 More details can be found in the psbasemap man pages.
74 CYLINDRICAL PROJECTIONS:
76 -Jclon0/lat0/scale (Cassini)
78 -Jcyl_stere/[lon0/[lat0/]]scale (Cylindrical Stereographic)
79 -Jj[lon0/]scale (Miller)
80 -Jm[lon0/[lat0/]]scale (Mercator)
81 -Jmlon0/lat0/scale (Mercator - Give meridian and standard paral‐
82 lel)
83 -Jo[a]lon0/lat0/azimuth/scale (Oblique Mercator - point and
84 azimuth)
85 -Jo[b]lon0/lat0/lon1/lat1/scale (Oblique Mercator - two points)
86 -Joclon0/lat0/lonp/latp/scale (Oblique Mercator - point and
87 pole)
88 -Jq[lon0/[lat0/]]scale (Cylindrical Equidistant)
89 -Jtlon0/[lat0/]scale (TM - Transverse Mercator)
90 -Juzone/scale (UTM - Universal Transverse Mercator)
91 -Jy[lon0/[lat0/]]scale (Cylindrical Equal-Area)
92 CONIC PROJECTIONS:
94 -Jblon0/lat0/lat1/lat2/scale (Albers)
96 -Jdlon0/lat0/lat1/lat2/scale (Conic Equidistant)
97 -Jllon0/lat0/lat1/lat2/scale (Lambert Conic Conformal)
98 AZIMUTHAL PROJECTIONS:
100 -Jalon0/lat0[/horizon]/scale (Lambert Azimuthal Equal-Area)
102 -Jelon0/lat0[/horizon]/scale (Azimuthal Equidistant)
103 -Jflon0/lat0[/horizon]/scale (Gnomonic)
104 -Jglon0/lat0[/horizon]/scale (Orthographic)
105 -Jglon0/lat0/altitude/azimuth/tilt/twist/Width/Height/scale
106 (General Perspective).
107 -Jslon0/lat0[/horizon][/slat]/scale (General Stereographic)
108 MISCELLANEOUS PROJECTIONS:
110 -Jh[lon0/]scale (Hammer)
112 -Ji[lon0/]scale (Sinusoidal)
113 -Jkf[lon0/]scale (Eckert IV)
114 -Jk[s][lon0/]scale (Eckert IV)
115 -Jn[lon0/]scale (Robinson)
116 -Jr[lon0/]scale (Winkel Tripel)
117 -Jv[lon0/]scale (Van der Grinten)
118 -Jw[lon0/]scale (Mollweide)
119 NON-GEOGRAPHICAL PROJECTIONS:
121 -Jp[a]scale[/origin][r|z] (Polar coordinates (theta,r))
123 -Jxx-scale[d|l|ppow|t|T][/y-scale[d|l|ppow|t|T]] (Linear, log,
124 and power scaling)
125 -M Output triangulation network as multiple line segments separated
127 by a record whose first character is flag [>]. To plot, use
128 psxy with the -M option (see Examples).
129 -R xmin, xmax, ymin, and ymax specify the Region of interest. For
131 geographic regions, these limits correspond to west, east,
132 south, and north and you may specify them in decimal degrees or
133 in [+-]dd:mm[:ss.xxx][W|E|S|N] format. Append r if lower left
134 and upper right map coordinates are given instead of w/e/s/n.
135 The two shorthands -Rg and -Rd stand for global domain (0/360
136 and -180/+180 in longitude respectively, with -90/+90 in lati‐
137 tude). For calendar time coordinates you may either give (a)
138 relative time (relative to the selected TIME_EPOCH and in the
139 selected TIME_UNIT; append t to -JX|x), or (b) absolute time of
140 the form [date]T[clock] (append T to -JX|x). At least one of
141 date and clock must be present; the T is always required. The
142 date string must be of the form [-]yyyy[-mm[-dd]] (Gregorian
143 calendar) or yyyy[-Www[-d]] (ISO week calendar), while the clock
144 string must be of the form hh:mm:ss[.xxx]. The use of delim‐
145 iters and their type and positions must be exactly as indicated
146 (however, input, output and plot formats are customizable; see
147 gmtdefaults).
148 -V Selects verbose mode, which will send progress reports to stderr
150 [Default runs "silently"].
151 -Z Controls whether binary data file has two or three columns [2].
153 Ignored if -b is not set.
154 -: Toggles between (longitude,latitude) and (latitude,longitude)
156 input and/or output. [Default is (longitude,latitude)]. Append
157 i to select input only or o to select output only. [Default
158 affects both].
159 -bi Selects binary input. Append s for single precision [Default is
161 d (double)]. Uppercase S or D will force byte-swapping.
162 Optionally, append ncol, the number of columns in your binary
163 input file if it exceeds the columns needed by the program. Or
164 append c if the input file is netCDF. Optionally, append
165 var1/var2/... to specify the variables to be read. [Default is
166 2 input columns].
167 -bo Selects binary output. Append s for single precision [Default
169 is d (double)]. Uppercase S or D will force byte-swapping.
170 Optionally, append ncol, the number of desired columns in your
171 binary output file. [Default is same as input]. Node ids are
172 stored as binary 4-byte integer triplets. -bo is ignored if -M
173 is selected.
174 -f Special formatting of input and/or output columns (time or geo‐
176 graphical data). Specify i or o to make this apply only to
177 input or output [Default applies to both]. Give one or more
178 columns (or column ranges) separated by commas. Append T (abso‐
179 lute calendar time), t (relative time in chosen TIME_UNIT since
180 TIME_EPOCH), x (longitude), y (latitude), or f (floating point)
181 to each column or column range item. Shorthand -f[i|o]g means
182 -f[i|o]0x,1y (geographic coordinates).
183
185 The ASCII output formats of numerical data are controlled by parameters
186 in your .gmtdefaults4 file. Longitude and latitude are formatted
187 according to OUTPUT_DEGREE_FORMAT, whereas other values are formatted
188 according to D_FORMAT. Be aware that the format in effect can lead to
189 loss of precision in the output, which can lead to various problems
190 downstream. If you find the output is not written with enough preci‐
191 sion, consider switching to binary output (-bo if available) or specify
192 more decimals using the D_FORMAT setting.
193
195 Regardless of the precision of the input data, GMT programs that create
196 gridded files will internally hold the grids in 4-byte floating point
197 arrays. This is done to conserve memory and futhermore most if not all
198 real data can be stored using 4-byte floating point values. Data with
199 higher precision (i.e., double precision values) will lose that preci‐
200 sion once GMT operates on the grid or writes out new grids. To limit
201 loss of precision when processing data you should always consider nor‐
202 malizing the data prior to processing.
203
205 To triangulate the points in the file samples.xyz, store the triangle
206 information in a binary file, and make a grid for the given area and
207 spacing, use
208 triangulate samples.xyz -bo -R0/30/0/30 -I2 -Gsurf.grd > samples.ijk
210 To draw the optimal Delauney triangulation network based on the same
212 file using a 15-cm-wide Mercator map, use
213 triangulate samples.xyz -M -R-100/-90/30/34 -JM15c | psxy -M
215 -R-100/-90/30/34 -JM15c -W0.5p -B1 > network.ps
216
218 GMT(1), pscontour(1)
219
221 Watson, D. F., 1982, Acord: Automatic contouring of raw data, Comp. &
222 Geosci., 8, 97-101.
223 Shewchuk, J. R., 1996, Triangle: Engineering a 2D Quality Mesh Genera‐
224 tor and Delaunay Triangulator, First Workshop on Applied Computational
225 Geometry (Philadelphia, PA), 124-133, ACM, May 1996.
226 www.cs.cmu.edu/~quake/triangle.html
227GMT 4.3.1 15 May 2008 TRIANGULATE(1)