healpixRingLon( k, index )Note: the index parameter is 0-based,
unlike the table row index special token $index
(a.k.a. $0), which is 1-based.
So if the HEALpix index is implicitly determined by the table row,
the value $index-1 should be used.
k (integer)index (long integer)double healpixRingLon(int, long)