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

6       c_csstrid - calculates a Delaunay triangulation for data on a sphere
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FUNCTION PROTOTYPE

9           int *c_csstrid(int, double [], double [], int *, int *);
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SYNOPSIS

13           int *c_csstrid(n, rlat, rlon, nt, ier);
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DESCRIPTION

17       n           The number of input data points, n > 2.
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19       rlat        An  array  containing  the  latitudes  of  the  input data,
20                   expressed in degrees.  The first three points must  not  be
21                   collinear (lie on a common great circle).
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23       rlon        An  array  containing  the  longitudes  of  the input data,
24                   expressed in degrees.
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26       nt          *nt is the number of triangles in the triangulation, unless
27                   *ier  is  non-zero, in which case *nt = 0.  Where nb is the
28                   number of boundary points on the convex hull of  the  data,
29                   if  nb is greater than 3, then *nt = 2n-nb-2, otherwise *nt
30                   = 2n-4.  The input data are considered  to  be  bounded  if
31                   they all lie in one hemisphere.
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33       ier         An  error  return  value. If *ier is returned as 0, then no
34                   errors were detected. If *ier is non-zero,  then  refer  to
35                   the error list in cssgrid_errors for details.
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USAGE

38       c_csstrid  is  called to find a Delaunay triangulation of data randomly
39       positioned on the surface of a sphere. c_csstrid is a double  precision
40       version of c_csstri.
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RETURN VALUE

43       c_csstrid  returns a pointer to a linear array that contains a sequence
44       of integer triples. The elements of a triple are indices of vertices of
45       a  triangle.  Each index references an original data point as it occurs
46       in sequence in the input data set (numbering starts at 0). For example,
47       if   the   triple   <5,0,2>   were   in   the  list  of  triples,  then
48       (rlat[5],rlon[5]), (rlat[0],rlon[0]), and  (rlat[2],rlon[2])  would  be
49       vertices of a triangle in the Delaunay triangulation.
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ACCESS

52       To use c_csstrid, load the NCAR Graphics library ngmath.
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SEE ALSO

55       css_overview, c_cssgrid, c_csstri, cssgrid_errors
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57       Complete documentation for Cssgrid is available at URL
58       http://ngwww.ucar.edu/ngdoc/ng/ngmath/cssgrid/csshome.html
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61       Copyright (C) 2000
62       University Corporation for Atmospheric Research
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64       The use of this Software is governed by a License Agreement.
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68UNIX                               May 2000                  c_csstrid(3NCARG)
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