NGGCOG - Returns the latitudes and longitudes of a set of points approximating a circle at a given point on the surface of the globe.
CALL NGGCOG (CLAT,CLON,CRAD,ALAT,ALON,NPTS)
void c_nggcog(float clat, float clon, float crad, float *alat,
float *alon, int npts)
- (an input expression of type REAL) is the latitude, in degrees, of a point on the globe defining the center of the circle.
- (an input expression of type REAL) is the longitude, in degrees, of a point on the globe defining the center of the circle.
- (an input expression of type REAL) specifies the radius of the circle. This is given as a great-circle distance, in degrees.
- (an output array, of type REAL, dimensioned NPTS) is an array in which the latitudes of points on the circle are to be returned.
- (an output array, of type REAL, dimensioned NPTS) is an array in which the longitudes of points on the circle are to be returned.
- (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.
The C binding argument descriptions are the same as the FORTRAN argument descriptions.
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.
Use the ncargex command to see the following relevant example: cpex10.
To use NGGCOG or c_nggcog, load the NCAR Graphics libraries ncarg, ncarg_gks, and ncarg_c, preferably in that order.
Online: nggsog(3NCARG), ngritd(3NCARG).
Copyright (C) 1987-2009
University Corporation for Atmospheric Research
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