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.

UNIX                                                May 2000                                    c_csvoro(3NCARG)