neighbours

astropy_healpix.neighbours(healpix_index, nside, order='ring')

Find all the HEALPix pixels that are the neighbours of a HEALPix pixel

Parameters:

healpix_indexndarray

Array of HEALPix pixels

nsideint

Number of pixels along the side of each of the 12 top-level HEALPix tiles

order{ ‘nested’ | ‘ring’ }

Order of HEALPix pixels

Returns:

neighndarray

Array giving the neighbours starting SW and rotating clockwise. This has one extra dimension compared to healpix_index - the first dimension - which is set to 8. For example if healpix_index has shape (2, 3), neigh has shape (8, 2, 3).

Notes

Some HEALPix pixels do not have all 8 neighbours. In these cases, the corresponding entry in the returned array has the value of -1 and Numpy may print an invalid value warning. To suppress the warning, use numpy.errstate.