NAME

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

SYNOPSIS

       sphtriangulate  [  table  ]  [   ] [  ] [  ] [ unit ] [ nfile ] [ d|v ] [  ] [ [level] ] [
       -b<binary> ] [ -d<nodata> ] [ -h<headers> ] [ -i<flags> ] [ -:[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 find 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 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.

       -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
              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.

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 -B0g30 | 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

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