xenial (1) sphtriangulate.1gmt.gz

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