1c_csvoro(3NCARG)                 NCAR GRAPHICS                c_csvoro(3NCARG)
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NAME

6       c_csvoro - calculate Voronoi polygons for points on a sphere.
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FUNCTION PROTOTYPE

9       void   c_csvoro(int, float [], float [],
10                       int, int, float [], float [], float [],
11                       int *, int *, int [], int *);
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SYNOPSIS

15       void *c_csvoro (n, rlat, rlon, ni, nf, plat, plon, rc,
16                       nca, numv, nv, ier);
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DESCRIPTION

20       n           The number of input data points, n > 2.
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22       rlat        An  array  containing  the  latitudes  of  the  input data,
23                   expressed in degrees.  The first three points must  not  be
24                   collinear (lie on a common great circle).
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26       rlon        An  array  containing  the  longitudes  of  the input data,
27                   expressed in degrees.
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29       ni          The index of the input coordinate for  which  you  want  to
30                   determine the Voronoi polygon (0 <= ni < n).
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32       nf          Flag  indicating  if  this is the first call to c_csvoro to
33                   retrieve Voronoi polygons for this dataset  (1=yes,  0=no).
34                   Calls  subsequent to the first call for a given dataset are
35                   much faster than the first call.
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37       plat        The latitudes for the vertices  of  the  Voronoi  polygons.
38                   These  are  circumcenters  of  circles  passing through the
39                   Delaunay triangles. If a coordinate is  a  boundary  point,
40                   then  the  circle  may pass through certain "pseudo points"
41                   that have been added to the original dataset  in  order  to
42                   complete the Voronoi polygon.
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44       plon        The longitudes for the vertices of the Voronoi polygons.
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46       rc          Array containing circumradii (arc lengths in degrees of the
47                   angle between a circumcenter and  its  associated  triangle
48                   vertices).
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50       nca         *nca is the actual number of circumcenters returned in plat
51                   and plon. This number may be larger than  n  if  the  input
52                   dataset  has boundary points, since certain "pseudo points"
53                   may have been added to the original  dataset  in  order  to
54                   complete the Voronoi polygon set.
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56       numv        *numv  is  the  number  of  vertices in the Voronoi polygon
57                   enclosing the coordinate (rlat[ni],rlon[ni]).
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59       nv          An array containing numv indices for  the  Voronoi  polygon
60                   enclosing  the  coordinate (rlat[ni],rlon[ni]). The indices
61                   returned in this array refer to the coordinates returned in
62                   plat  and plon.  For example, if the integer "j" is an ele‐
63                   ment of the nv array, then (plat[j],plon[j]) is a vertex of
64                   the  Voronoi  polygon  enclosing  (rlat[ni],rlon[ni]).  The
65                   indices in nv list out the vertices of the Voronoi  polygon
66                   in counter-clockwise order.
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68       ier         An  error  return  value. If *ier is returned as 0, then no
69                   errors were detected. If *ier is non-zero,  then  refer  to
70                   the error list in the error table for details.
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USAGE

73       c_csvoro  is  called  if you want to determine the Voronoi polygons for
74       data randomly positioned on a sphere. Each call to c_csvoro  calculates
75       the  vertices  for  the  Voronoi  polygon surrounding a specified input
76       point.
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ACCESS

79       To use c_csvoro, load the NCAR Graphics library ngmath.
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SEE ALSO

82       css_overview, c_cssgrid, cssgrid_errors
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84       Complete documentation for Cssgrid is available at URL
85       http://ngwww.ucar.edu/ngdoc/ng/ngmath/cssgrid/csshome.html
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88       Copyright (C) 2000
89       University Corporation for Atmospheric Research
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91       The use of this Software is governed by a License Agreement.
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95UNIX                               May 2000                   c_csvoro(3NCARG)
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