match_coordinates_3d

astropy.coordinates.match_coordinates_3d(matchcoord, catalogcoord, nthneighbor=1, storekdtree='kdtree_3d')

Finds the nearest 3-dimensional matches of a coordinate or coordinates in a set of catalog coordinates.

This finds the 3-dimensional closest neighbor, which is only different from the on-sky distance if distance is set in either matchcoord or catalogcoord.

Parameters:

matchcoord : BaseCoordinateFrame or SkyCoord

The coordinate(s) to match to the catalog.

catalogcoord : BaseCoordinateFrame or SkyCoord

The base catalog in which to search for matches. Typically this will be a coordinate object that is an array (i.e., catalogcoord.isscalar == False)

nthneighbor : int, optional

Which closest neighbor to search for. Typically 1 is desired here, as that is correct for matching one set of coordinates to another. The next likely use case is 2, for matching a coordinate catalog against itself (1 is inappropriate because each point will find itself as the closest match).

storekdtree : bool or str, optional

If a string, will store the KD-Tree used for the computation in the catalogcoord, as in catalogcoord.cache with the provided name. This dramatically speeds up subsequent calls with the same catalog. If False, the KD-Tree is discarded after use.

Returns:

idx : integer array

Indices into catalogcoord to get the matched points for each matchcoord. Shape matches matchcoord.

sep2d : Angle

The on-sky separation between the closest match for each matchcoord and the matchcoord. Shape matches matchcoord.

dist3d : Quantity

The 3D distance between the closest match for each matchcoord and the matchcoord. Shape matches matchcoord.

Notes

This function requires SciPy to be installed or it will fail.