Provided by: gmt-common_5.4.5+dfsg-1_all bug

NAME

       sphtriangulate - Delaunay or Voronoi construction of spherical lon,lat data

SYNOPSIS

       sphtriangulate [ table ] [  -A ] [  -C ] [  -D ] [  -Lunit ] [  -Nnfile ] [  -Qd|v ] [  -T
       ] [  -V[level] ] [ -bbinary ] [ -dnodata ] [ -eregexp ]  [  -hheaders  ]  [  -iflags  ]  [
       -:[i|o] ]

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

DESCRIPTION

       sphtriangulate  reads  one  or more ASCII [or binary] files (or standard input) containing
       lon, lat and performs a spherical Delaunay triangulation,  i.e.,  it  determines  how  the
       points  should  be  connected  to  give the most equilateral triangulation possible on the
       sphere. Optionally, you may choose -Qv which will do  further  processing  to  obtain  the
       Voronoi  polygons.  Normally,  either  set  of polygons will be written as closed fillable
       segment output; use -T to write unique arcs instead. As an option,  compute  the  area  of
       each triangle or polygon. The algorithm used is STRIPACK.

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.

       -A     Compute the area of the spherical triangles (-Qd) or polygons (-Qv) and  write  the
              areas  (in  chosen  units;  see  -L)  in  the  output  segment  headers  [no  areas
              calculated].

       -C     For large data set you can save some memory (at the expense of more processing)  by
              only storing one form of location coordinates (geographic or Cartesian 3-D vectors)
              at any given time, translating from one form to the other when  necessary  [Default
              keeps both arrays in memory].

       -D     Used  to skip the last (repeated) input vertex at the end of a closed segment if it
              equals the first point in the segment.  [Default uses all points].

       -Lunit Specify the unit used for distance and area calculations. Choose  among  e  (m),  f
              (foot),  k  (km),  m  (mile),  n  (nautical mile), u (survey foot), or d (spherical
              degree). A spherical approximation is used  unless  PROJ_ELLIPSOID  is  set  to  an
              actual  ellipsoid,  in which case we convert latitudes to authalic latitudes before
              calculating areas. When degree is selected the areas are given in steradians.

       -Nnfile
              Write the information pertaining to each polygon.  For  Delaunay:  the  three  node
              number  and the triangle area (if -A was set); for Voronoi the unique node lon, lat
              and polygon area (if -A was set)) to a separate  file.  This  information  is  also
              encoded  in the segment headers of ASCII output files. Required if binary output is
              needed.

       -Qd|v  Append d for Delaunay triangles or v for Voronoi polygons [Delaunay].   If  -bo  is
              used  then  -N may be used to specify a separate file where the polygon information
              normally is written.

       -T     Write the unique arcs of the construction [Default  writes  fillable  triangles  or
              polygons].  When  used  with -A we store arc length in the segment header in chosen
              unit (see -L).

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

       -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].

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

       -e[~]"pattern" | -e[~]/regexp/[i] (more ...)
              Only accept data records that match the given pattern.

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

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

       -r (more ...)
              Set pixel node registration [gridline].

       -^ 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  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  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 FORMAT_DATE_OUT and FORMAT_CLOCK_OUT, whereas general floating point
       values are formatted according to FORMAT_FLOAT_OUT. Be aware that the format 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 setting.

EXAMPLES

       To  triangulate  the points in the file testdata.txt, and make a Voronoi diagram via psxy,
       use

              gmt sphtriangulate testdata.txt -Qv | psxy -Rg -JG30/30/6i -L -P -W1p -Bag | gv -

       To compute the optimal Delaunay triangulation network based on the multiple  segment  file
       globalnodes.d and save the area of each triangle in the header record, try

              gmt sphtriangulate globalnodes.d -Qd -A > global_tri.d

SEE ALSO

       gmt, triangulate, sphdistance

REFERENCES

       Renka, R, J., 1997, Algorithm 772: STRIPACK: Delaunay Triangulation and Voronoi Diagram on
       the Surface of a Sphere, AMC Trans. Math. Software, 23(3), 416-434.

COPYRIGHT

       2019, P. Wessel, W. H. F. Smith, R. Scharroo, J. Luis, and F. Wobbe