# ncl_c_csstrid - Man Page

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

n

The number of input data points, n > 2.

rlat

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).

rlon

An array containing the longitudes of the input data, expressed in degrees.

nt

*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.

ier

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,rlon), (rlat,rlon), and (rlat,rlon) would be vertices of  a triangle in the Delaunay triangulation.

## Access

To use c_csstrid, load the NCAR Graphics library ngmath.