c_csstrid(3NCARG) NCAR GRAPHICS c_csstrid(3NCARG)

# NAME¶

c_csstrid - calculates a Delaunay triangulation for data on a sphere

# FUNCTION PROTOTYPE¶

```
int *c_csstrid(int, double [], double [], int *, int *);```

# SYNOPSIS¶

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

# DESCRIPTION¶

The number of input data points, n > 2.
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).
An array containing the longitudes of the input data, expressed in degrees.
*nt is the number of triangles in the triangulation, unless *ier is non-zero, in which case *nt = 0. Where nb is the number of boundary points on the convex hull of the data, if nb is greater than 3, then *nt = 2n-nb-2, otherwise *nt = 2n-4. The input data are considered to be bounded if they all lie in one hemisphere.
An error return value. If *ier is returned as 0, then no errors were detected. If *ier is non-zero, then refer to the error list in cssgrid_errors for details.

# USAGE¶

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

# RETURN VALUE¶

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

# ACCESS¶

To use c_csstrid, load the NCAR Graphics library ngmath.