NAME

       c_csvoro - calculate Voronoi polygons for points on a sphere.

FUNCTION PROTOTYPE

       void   c_csvoro(int, float [], float [],
                       int, int, float [], float [], float [],
                       int *, int *, int [], int *);

SYNOPSIS

       void *c_csvoro (n, rlat, rlon, ni, nf, plat, plon, rc,
                       nca, numv, nv, ier);

DESCRIPTION

       n           The number of input data points, n > 2.

       rlat        An  array  containing the latitudes of the input data, expressed in degrees.  The first three
                   points must not be collinear (lie on a common great circle).

       rlon        An array containing the longitudes of the input data, expressed in degrees.

       ni          The index of the input coordinate for which you want to determine the Voronoi polygon  (0  <=
                   ni < n).

       nf          Flag  indicating  if this is the first call to c_csvoro to retrieve Voronoi polygons for this
                   dataset (1=yes, 0=no). Calls subsequent to the first call for a given dataset are much faster
                   than the first call.

       plat        The  latitudes  for the vertices of the Voronoi polygons.  These are circumcenters of circles
                   passing through the Delaunay triangles. If a coordinate is a boundary point, then the  circle
                   may  pass  through  certain  "pseudo  points" that have been added to the original dataset in
                   order to complete the Voronoi polygon.

       plon        The longitudes for the vertices of the Voronoi polygons.

       rc          Array containing circumradii (arc lengths in degrees of the angle between a circumcenter  and
                   its associated triangle vertices).

       nca         *nca  is  the  actual  number  of circumcenters returned in plat and plon. This number may be
                   larger than n if the input dataset has boundary points, since  certain  "pseudo  points"  may
                   have been added to the original dataset in order to complete the Voronoi polygon set.

       numv        *numv   is   the  number  of  vertices  in  the  Voronoi  polygon  enclosing  the  coordinate
                   (rlat[ni],rlon[ni]).

       nv          An  array  containing  numv  indices  for  the  Voronoi  polygon  enclosing  the   coordinate
                   (rlat[ni],rlon[ni]).  The indices returned in this array refer to the coordinates returned in
                   plat and plon.  For example, if the  integer  "j"  is  an  element  of  the  nv  array,  then
                   (plat[j],plon[j])  is  a  vertex  of  the  Voronoi polygon enclosing (rlat[ni],rlon[ni]). The
                   indices in nv list out the vertices of the Voronoi polygon in counter-clockwise order.

       ier         An error return value. If *ier is returned as 0, then no errors were  detected.  If  *ier  is
                   non-zero, then refer to the error list in the error table for details.

USAGE

       c_csvoro  is  called  if  you  want  to  determine the Voronoi polygons for data randomly positioned on a
       sphere. Each call to c_csvoro calculates the vertices for the Voronoi  polygon  surrounding  a  specified
       input point.

ACCESS

       To use c_csvoro, load the NCAR Graphics library ngmath.

SEE ALSO

       css_overview, c_cssgrid, cssgrid_errors

       Complete documentation for Cssgrid is available at URL
       http://ngwww.ucar.edu/ngdoc/ng/ngmath/cssgrid/csshome.html

COPYRIGHT

       Copyright (C) 2000
       University Corporation for Atmospheric Research

       The use of this Software is governed by a License Agreement.