ncl_nggcog - Man Page

Returns the latitudes and longitudes of a set of points approximating a circle at a given point on the surface of the globe.

Synopsis

CALL NGGCOG (CLAT,CLON,CRAD,ALAT,ALON,NPTS)

C-Binding Synopsis

#include <ncarg/ncargC.h>

void c_nggcog(float clat, float clon, float crad, float *alat,
float *alon, int npts)

Description

CLAT: (an input expression of type REAL) is the latitude, in degrees, of a point on the globe defining the center of the circle.
CLON: (an input expression of type REAL) is the longitude, in degrees, of a point on the globe defining the center of the circle.
CRAD: (an input expression of type REAL) specifies the radius of the circle. This is given as a great-circle distance, in degrees.
ALAT: (an output array, of type REAL, dimensioned NPTS) is an array in which the latitudes of points on the circle are to be returned.
ALON: (an output array, of type REAL, dimensioned NPTS) is an array in which the longitudes of points on the circle are to be returned.
NPTS: (an input expression, of type INTEGER) is the desired number of points to be used to represent the circle. Its value determines how accurately the circle will be represented.

C-Binding Description

The C binding argument descriptions are the same as the FORTRAN argument descriptions.

Usage

Let C represent (CLAT,CLON) and let O represent the center of the globe. The circle is the set of all points P on the globe such that the angle POC is of the size specified by CRAD.

SIN and COS are used to generate points representing a circle having the desired radius and centered at the North Pole. These points are then subjected to two rotations - one that brings the circle down to the desired latitude, and another that carries it to the desired longitude.