# ncl_csstrid - Man Page

calculates a Delaunay triangulation for data on a sphere

## Synopsis

CALL CSSTRID (N, RLAT, RLON, NT, NTRI, IWK, RWK, IER)

## Description

- N
(integer,input) The number of input data points (N > 2).

- RLAT
(double precision, 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).

- RLON
(double precision, input) An array containing the longitudes of the input data, expressed in degrees.

- NT
(integer, output) The number of triangles in the triangulation, unless IER .NE. 0, in which case NT = 0. Where NB is the number of boundary points on the convex hull of the data, if NB .GE. 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. Dimensioning NT for 2*N will always work.

- NTRI
(integer, output) A two-dimensional integer array dimensioned for 3 x NT where NT is the number of triangles in the triangulation (NT is at most 2*N). NTRI contains the triangulation data. The vertices of the Kth triangle are: (PLAT(NTRI((1,K)),PLON(NTRI(1,K)), (PLAT(NTRI((2,K)),PLON(NTRI(2,K)), (PLAT(NTRI((3,K)),PLON(NTRI(3,K))

- IWK
(integer, input) An integer workspace of length 27*N.

- RWK
(double precision, input) A work array dimensioned for 13*N. Note that this work array must be typed DOUBLE PRECISION.

- 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

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

## Access

To use CSSTRID, load the NCAR Graphics library ngmath.

## See Also

css_overview, cssgrid, csstri, csvoro.

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.