NAME

       CSVORO - calculate Voronoi polygons for data on a sphere.

SYNOPSIS

       CALL CSVORO (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       (real, 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       (real, 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  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.

       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       (real,  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       (real, output) The longitudes for the vertices of the Voronoi polygons.

       RC          (real, 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

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

ACCESS

       To use CSVORO, load the NCAR Graphics library ngmath.

SEE ALSO

       css_overview, csstri, cssgrid.

       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                                      CSVORO(3NCARG)