NAME

       CSVOROD - calculate Voronoi polygons for data on a sphere.

SYNOPSIS

       CALL CSVOROD (NPTS, RLATI, RLONI, NI, NF, IWK, RWK,
                    NC, RLATO, RLONO, RC,
                    NCA, NUMV, NV, IER)

DESCRIPTION

       NPTS        (integer,input) The number of input data points (NPTS > 3).

       RLATI       (double precision, input) 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).

       RLONI       (double  precision,  input)  An  array  containing the longitudes of the input
                   data, expressed in degrees.

       NI          (integer, input) The index of the input  coordinate  for  which  you  want  to
                   determine the Voronoi polygon (1 .LE. NI .LE. NPTS).

       NF          (integer,  input)  Flag  indicating  if  this  is the first call to CSVOROD 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.

       IWK         (integer, input) Integer work space dimensioned for 27*NPTS.

       RWK         (double  precision, input) A work space dimensioned for 9*NPTS.  Note that RWK
                   must be typed DOUBLE PRECISION.

       NC          (integer, input) The maximum size of the output arrays RLATO, RLONO,  and  RC.
                   NC should be 2*NPTS.

       RLATO       (double  precision,  output)  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.

       RLONO       (double  precision,  output)  The  longitudes  for the vertices of the Voronoi
                   polygons.

       RC          (double precision,  output)  Array  containing  circumradii  (arc  lengths  in
                   degrees  of  the  angle  between  a  circumcenter  and its associated triangle
                   vertices).

       NCA         (integer, output) The actual number of circumcenters  returned  in  RLATO  and
                   RLONO.  This  number may be larger than NPTS 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        (integer,  output) The number of vertices in the Voronoi polygon enclosing the
                   coordinate (RLATI(NI),RLONI(NI)).

       NV          (integer, output) An array (dimensioned for NPTS) containing NUMV indices  for
                   the  Voronoi  polygon  enclosing  the  coordinate  (RLATI(NI),RLONI(NI)).  The
                   indices returned in this array refer to the  coordinates  returned  in  RLATO,
                   RLONO,  and RC. For example, if the integer "J" is an element of the NV array,
                   then  (RLATO(J),RLONO(J))  is  a  vertex  of  the  Voronoi  polygon  enclosing
                   (RLATI(NI),RLONI(NI)).  The indices in NV list out the vertices of the Voronoi
                   polygon in counter-clockwise order.

       IER         (integer, output) An error return value.  If IER is returned  as  0,  then  no
                   errors  were  detected.  If  IER  is  non-zero, then refer to the man page for
                   cssgrid_errors for details.

USAGE

       CSVOROD is called if you  want  to  determine  the  Voronoi  polygons  for  data  randomly
       positioned  on  a  sphere.  Each  call  to CSVOROD calculates the vertices for the Voronoi
       polygon surrounding a specified input point.  CSVOROD is a  double  precision  version  of
       CSVORO.

ACCESS

       To use CSVOROD, load the NCAR Graphics library ngmath.

SEE ALSO

       css_overview, csstrid, cssgridd.

       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.