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.

UNIX                                                May 2000                                     CSVOROD(3NCARG)