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.