triangulate(1) GMT triangulate(1)
NAME
triangulate - Do optimal (Delaunay) triangulation and gridding of
Cartesian table data [method]
SYNOPSIS
triangulate [ table ] [ -Cslpfile ] [ -Dx|y ] [ -Eempty ] [ -Ggrd-
file ] [ -Iincrement ] [ -Jparameters ] [ -M ] [ -N ] [ -Q[n] ] [
-Rregion ] [ -S ] [ -V[level] ] [ -Z ] [ -bbinary ] [ -dnodata ] [
-eregexp ] [ -fflags ] [ -hheaders ] [ -iflags ] [ -r ] [ -:[i|o] ]
Note: No space is allowed between the option flag and the associated
arguments.
DESCRIPTION
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. Furthermore, if the
Shewchuk algorithm is installed then you can also perform the calcula-
tion of Voronoi polygons and optionally grid your data via the natural
nearest neighbor algorithm.
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.
-Cslpfile
Read a slope grid (in radians) and compute the propagated uncer-
tainty in the
bathymetry using the CURVE algorithm [Zambo et al, 20xx].
Requires the -G option to specify the output grid. Note
that the slpgrid sets the domain for the output grid so
-R, -I, [-r] are not required. Cannot be used in con-
junction with -D, -F, -M, -N, -Q, -S and -T.
-Dx|y Take either the x- or y-derivatives of surface represented by
the planar facets (only used when -G is set).
-Eempty
Set the value assigned to empty nodes when -G is set [NaN].
-Ggrdfile
Use triangulation to grid the data onto an even grid (specified
with -R -I). Append the name of the output grid file. The inter-
polation 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) or instead select sph-
triangulate. For natural nearest neighbor gridding you must add
-Qn.
-Ixinc[unit][+e|n][/yinc[unit][+e|n]]
x_inc [and optionally y_inc] is the grid spacing. Optionally,
append a suffix modifier. Geographical (degrees) coordinates:
Append m to indicate arc minutes or s to indicate arc seconds.
If one of the units e, f, k, M, n or u is appended instead, the
increment is assumed to be given in meter, foot, km, Mile, nau-
tical mile or US survey foot, respectively, and will be con-
verted to the equivalent degrees longitude at the middle lati-
tude of the region (the conversion depends on PROJ_ELLIPSOID).
If y_inc is given but set to 0 it will be reset equal to x_inc;
otherwise it will be converted to degrees latitude. All coordi-
nates: If +e is appended then the corresponding max x (east) or
y (north) may be slightly adjusted to fit exactly the given
increment [by default the increment may be adjusted slightly to
fit the given domain]. Finally, instead of giving an increment
you may specify the number of nodes desired by appending +n to
the supplied integer argument; the increment is then recalcu-
lated from the number of nodes and the domain. The resulting
increment value depends on whether you have selected a grid-
line-registered or pixel-registered grid; see App-file-formats
for details. Note: if -Rgrdfile is used then the grid spacing
has already been initialized; use -I to override the values.
-Jparameters (more a|)
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[n] Output the edges of the Voronoi cells instead [Default is Delau-
nay triangle edges]. Requires -R and is only available if linked
with the Shewchuk [1996] library. Note that -Z is ignored on
output. Optionally, append n for combining the edges into closed
Voronoi polygons.
-Rxmin/xmax/ymin/ymax[+r][+uunit] (more a|)
Specify the region of interest.
-S Output triangles as polygon segments separated by a segment
header record. Requires Delaunay triangulation.
-T Output edges or polygons even if gridding has been selected with
the -G option [Default will not output the triangulation or
Voronoi polygons is gridding is selected].
-V[level] (more a|)
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 a|)
Select native binary input. [Default is 2 input columns].
-bo[ncols][type] (more a|)
Select native binary output. [Default is same as input]. Node
ids are stored as double triplets.
-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.
-f[i|o]colinfo (more a|)
Specify data types of input and/or output columns.
-h[i|o][n][+c][+d][+rremark][+rtitle] (more a|)
Skip or produce header record(s).
-icols[+l][+sscale][+ooffset][,^<i>a|] (more a|)
Select input columns and transformations (0 is first column).
-r (more a|)
Set pixel node registration [gridline]. (Only valid with -G).
-:[i|o] (more a|)
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 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.
GRID VALUES PRECISION
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 preci-
sion once GMT operates on the grid or writes out new grids. To limit
loss of precision when processing data you should always consider nor-
malizing the data prior to processing.
EXAMPLES
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
To combine the Voronoi outlines into polygons and paint them according
to their ID, try
gmt triangulate samples.xyz -M -Qn -R-100/-90/30/34 -JM15c | \
gmt psxy -R-100/-90/30/34 -JM15c -W0.5p+cf -L -B1 -Ccolors.cpt -L > polygons.ps
To grid the data using the natural nearest neighbor algorithm, try
gmt triangulate samples.xyz -Gnnn.nc -Qn -R-100/-90/30/34 -I0.5
NOTES
The uncertainty propagation for bathymetric grids requires both hori-
zontal and vertical uncertainties and these are weighted given the
local slope. See the references for more details.
SEE ALSO
gmt(1), greenspline(1), nearneighbor(1), pscontour(1), sphdistance(1),
sphinterpolate(1), sphtriangulate(1), surface(1)
REFERENCES
Watson, D. F., 1982, Acord: Automatic contouring of raw data, Comp. &
Geosci., 8, 97-101.
Shewchuk, J. R., 1996, Triangle: Engineering a 2D Quality Mesh Genera-
tor and Delaunay Triangulator, First Workshop on Applied Computational
Geometry (Philadelphia, PA), 124-133, ACM, May 1996.
Shewchuk^<i>as Homepage
COPYRIGHT
2017, P. Wessel, W. H. F. Smith, R. Scharroo, J. Luis, and F. Wobbe
5.4.2 Jun 24, 2017 triangulate(1)
gmt5 5.4.2 - Generated Thu Jun 29 16:45:40 CDT 2017