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triangulate - Do optimal (Delaunay) triangulation and gridding of Cartesian table data


triangulate [ table ] [ x|y ] [ empty ] [ grdfile ] [ increment ] [ parameters ] [ ] [ ]
[ ] [ region ] [ ] [ [level] ] [ ] [ -b<binary> ] [ -d<nodata> ] [ -f<flags> ] [
-h<headers> ] [ -i<flags> ] [ -r ] [ -:[i|o] ]

Note: No space is allowed between the option flag and the associated arguments.


triangulate reads one or more ASCII [or binary] files (or standard input) containing
x,y[,z] and performs Delaunay triangulation, i.e., it find how the points should be
connected to give the most equilateral triangulation possible. If a map projection (give
-R and -J) is chosen then it is applied before the triangulation is calculated. By
default, the output is triplets of point id numbers that make up each triangle and is
written to standard output. The id numbers refer to the points position (line number,
starting at 0 for the first line) in the input file. As an option, you may choose to
create a multiple segment file that can be piped through psxy to draw the triangulation
network. If -G -I are set a grid will be calculated based on the surface defined by the
planar triangles. The actual algorithm used in the triangulations is either that of Watson
[1982] [Default] or Shewchuk [1996] (if installed; type triangulate - to see which method
is selected). This choice is made during the GMT installation.




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.

-Dx|y Take either the x- or y-derivatives of surface represented by the planar facets
(only used when -G is set).

Set the value assigned to empty nodes when -G is set [NaN].

Use triangulation to grid the data onto an even grid (specified with -R -I). Append
the name of the output grid file. The interpolation is performed in the original
coordinates, so if your triangles are close to the poles you are better off
projecting all data to a local coordinate system before using triangulate (this is
true of all gridding routines).

-I x_inc [and optionally y_inc] sets the grid size for optional grid output (see -G).
Append m to indicate arc minutes or s to indicate arc seconds.

-Jparameters (more ...)
Select map projection.

-M Output triangulation network as multiple line segments separated by a segment
header record.

-N Used in conjunction with -G to also write the triplets of the ids of all the
Delaunay vertices [Default only writes the grid].

-Q Output the edges of the Voronoi cells instead [Default is Delaunay triangle edges].
Requires -R and is only available if linked with the Shewchuk [1996] library. Note
that -Z is ignored on output.

-R[unit]xmin/xmax/ymin/ymax[r] (more ...)
Specify the region of interest.

-S Output triangles as polygon segments separated by a segment header record. Requires
Delaunay triangulation.

-V[level] (more ...)
Select verbosity level [c].

-Z Controls whether we read (x,y) or (x,y,z) data and if z should be output when -M or
-S are used [Read (x,y) only].

-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]. Node ids are stored as
double triplets.

-d[i|o]nodata (more ...)
Replace input columns that equal nodata with NaN and do the reverse on output.

-f[i|o]colinfo (more ...)
Specify data types of input and/or output columns.

-h[i|o][n][+c][+d][+rremark][+rtitle] (more ...)
Skip or produce header record(s).

-icols[l][sscale][ooffset][,...] (more ...)
Select input columns (0 is first column).

-r (more ...)
Set pixel node registration [gridline]. (Only valid with -G).

-:[i|o] (more ...)
Swap 1st and 2nd column on input and/or output.

-^ 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

Print GMT version and exit.

Print full path to GMT share directory and exit.


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, whereas other
values are formatted according to FORMAT_FLOAT_OUT. Be aware that the format in effect can
lead to loss of precision in the 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 setting.


Regardless of the precision of the input data, GMT programs that create grid files will
internally hold the grids in 4-byte floating point arrays. This is done to conserve memory
and furthermore most if not all real data can be stored using 4-byte floating point
values. Data with higher precision (i.e., double precision values) will lose that
precision once GMT operates on the grid or writes out new grids. To limit loss of
precision when processing data you should always consider normalizing the data prior to


To triangulate the points in the file samples.xyz, store the triangle information in a
binary file, and make a grid for the given area and spacing, use

gmt triangulate samples.xyz -bo -R0/30/0/30 -I2 -Gsurf.nc > samples.ijk

To draw the optimal Delaunay triangulation network based on the same file using a
15-cm-wide Mercator map, use

gmt triangulate samples.xyz -M -R-100/-90/30/34 -JM15c | gmt psxy \
-R-100/-90/30/34 -JM15c -W0.5p -B1 > network.ps

To instead plot the Voronoi cell outlines, try

gmt triangulate samples.xyz -M -Q -R-100/-90/30/34 -JM15c | \
gmt psxy -R-100/-90/30/34 -JM15c -W0.5p -B1 > cells.ps

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