xenial (1) triangulate.1gmt.gz

Provided by: gmt-common_5.2.1+dfsg-3build1_all bug

NAME

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

SYNOPSIS

       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.

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.

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.

       -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  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 exits.

       --version
              Print GMT version and exit.

       --show-datadir
              Print full path to GMT share directory and exit.

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, 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.

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 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
       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

SEE ALSO

       gmt, greenspline, nearneighbor, pscontour, sphinterpolate, sphtriangulate, surface

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 Generator and Delaunay Triangulator, First
       Workshop on Applied Computational Geometry (Philadelphia, PA), 124-133, ACM, May 1996.

       Shewchuk's Homepage

       2015, P. Wessel, W. H. F. Smith, R. Scharroo, J. Luis, and F. Wobbe