tmatchn: Crossmatches multiple tables using flexible criteria
tmatchn performs efficient and flexible crossmatching
between multiple tables.
It can match rows on the basis of their relative position in the sky,
or alternatively using many other criteria such as separation in
in some isotropic or anisotropic Cartesian space,
identity of a key value, or some combination of these;
the full range of match criteria is dicussed in Section 7.1.
Since the match criteria define what counts as a match between two
objects, it is not immediately obvious what is meant by a multi-table
match. In fact the command can work in one of two distinct modes,
controlled by the multimode parameter.
In pairs mode, one table (by default the first input table)
is designated the reference table, and pair matches between each of the
other tables and that one are identified.
In group mode groups of objects from all the input tables are
identified, as discussed in Section 7.2.
Currently, in both cases an output matched row cannot contain more
than one object from each input table.
Options for output of multiple rows per input table per match may be
forthcoming in future releases if there is demand.
tmatchn is intended for use with more than two input tables -
see tmatch1
and tmatch2
for 1- and 2-table crossmatching respectively.