spherematch

cosmo_utils.mock_catalogues.spherematch.spherematch(ra1, dec1, ra2, dec2, tol=None, nnearest=1, nthreads=1)[source] [edit on github]

Determines the matches between two catalogues of sources with <ra, dec> coordinates.

Parameters:

ra1, dec1 : array_like

Right ascension and declination of the 1st catalogue. Units are in degrees.

ra2, dec2 : array_like

Right ascension and declination of the 2nd catalogue. Units are in degrees.

tol : float or None, optional

How close (in degrees) a match has to be to count as a match. If None, all nearest neighbors for the 1st catalogue will be returned.

nnearest : int, optional

The nth neighbor to find. E.g. 1 for the nearest nearby, 2 for the second nearest neighbor, etc. Partcularly useful if you want to get the nearest non-self neighbor of a catalogue. To do this use:

``spherematch(ra, dec, ra, dec, nnearest=2)``

if nnearest == 0, all matches are returned.

nthreads : int, optional

Number of threads to use for calculation. This variable is set to 1 by default. Must be larger than 1.

Returns:

idx1 : int numpy.ndarray

Indices of the 1st catalogue of the matches. Will never be larger than ra1/dec1.

idx2 : int numpy.ndarray

Indices of the 2nd catalogue of the matches. Will never be larger than ra1/dec1.

ds : float numpy.ndarray

Distance (in degrees) between the matches.