def make_kdtree(ra, decl):
<EOL>cosdecl = np.cos(np.radians(decl))<EOL>sindecl = np.sin(np.radians(decl))<EOL>cosra = np.cos(np.radians(ra))<EOL>sinra = np.sin(np.radians(ra))<EOL>xyz = np.column_stack((cosra*cosdecl,sinra*cosdecl, sindecl))<EOL>kdt = sps.cKDTree(xyz,copy_data=True)<EOL>return kdt<EOL>
This makes a `scipy.spatial.CKDTree` on (`ra`, `decl`).

    Parameters
    ----------

    ra,decl : array-like
        The right ascension and declination coordinate pairs in decimal degrees.

    Returns
    -------

    `scipy.spatial.CKDTree`
        The cKDTRee object generated by this function is returned and can be
        used to run various spatial queries.