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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
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