Function healpixRingIndex( k, lon, lat )

Description:
Gives the pixel index for a given sky position in the HEALPix RING scheme.
Parameters:
k (integer)
HEALPix order (0..29)
lon (floating point)
longitude in degrees
lat (floating point)
latitude in degrees
Return Value (long integer):
pixel index
See Also:
HEALPix web site
Signature:
long healpixRingIndex(int, double, double)