NAME

NGGCOG - 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.

EXAMPLES

Use the ncargex command to see the following relevant example: cpex10.

ACCESS

To use NGGCOG or c_nggcog, load the NCAR Graphics libraries ncarg, ncarg_gks, and ncarg_c, preferably in that order.

MESSAGES

None.

SEE ALSO

Online: nggsog(3NCARG), ngritd(3NCARG).

COPYRIGHT

Copyright (C) 1987-2009
University Corporation for Atmospheric Research
The use of this Software is governed by a License Agreement.