spheregroup¶
-
pydl.pydlutils.spheregroup.
spheregroup
(ra, dec, linklength, chunksize=None)[source]¶ Perform friends-of-friends grouping given ra/dec coordinates.
Parameters: ra, dec :
numpy.ndarray
Arrays of coordinates to group in decimal degrees.
linklength :
float
Linking length for the groups in decimal degrees.
chunksize :
float
, optionalBreak up the sphere into chunks of this size in decimal degrees.
Returns: A tuple containing the group number of each object, the multiplicity of each group, the first member of each group, and the next member of the group for each object.
Raises: PydlutilsException
If the array of coordinates only contains one point.
Notes
It is important that
chunksize
>= 4 *linklength
. This is enforced.Warning
Behavior at the poles is not well tested.