DM-33012 Update faro base class refcat loader to return single DataFrame

[psferguson]

Previously the _getReferenceCatalog returned the loaded refcat and a corrected refcat.
The corrected refcat had color trasformations applied, but had a nested list containing these magnitudes.
This caused downstream problems in using the matchter_probablistic task.

The _getReferenceCatalog has been updated to return a single data frame that is a hstack of the refCat, and refCatCorrected.

[bechtol]

The returns have changed such that refCat and refCatCorrected are no longer being returned. In that case, these should be removed from the list of returns in the documentation. I think it is still useful to have the documentation that describes what is included in the merged reference catalog DataFrame, but maybe this information goes in the docstring after the one-line description and before the listing of Parameters.

[psferguson]

Agreed this docstring has been changed with a longer description at the beginning and the following returns

Returns
-------
refCat: pandas.dataframe
a reference catalog with original columns and corrected
coordinates (ra,dec) and reference magnitudes (refMag-/refMagErr)

[bechtol]

Would it make sense to change refCatFrame -> refCat since downstream users of the reference catalog will simply expect a DataFrame?

[psferguson]

It also occurs to me that we may want to make sure there are no duplicate columns, and if there are probably supersede the catalog columns with the corrected columns.
This sort of occurs with coord_ra/dec which gets converted from radians to degrees.
But I could also imagine the magnitudes having the same column names in the refcat and filterList.

[bechtol]

Yes, it would be a good idea to check for any duplicated columns. However, doesn't the refMag- prefix make it unlikely to have a conflict of the column names for magnitudes? I think also the ra dec is unlikely to create a conflict because the reference catalog uses coord_ra and coord_dec as the standard coordinate column names -- is that correct?

[psferguson]

Ah your are right, I had misremembered about adding the refMag prefix in. This should not not be an issue.
Do we want to return both coord_ra and ra or just the corrected version?

[bechtol]

Ah your are right, I had misremembered about adding the refMag prefix in. This should not not be an issue. Do we want to return both coord_ra and ra or just the corrected version?

My inclination is return both at least for now (partly as a check that proper motions have been applied). In that case, we will need to be clear in the documentation about the meaning of (and distinction between) the two columns.

[bechtol]

Suggest (refMag-/refMagErr-) and also below just for consistency.

The doc string might want to use the words "color terms" when referring to the reference magnitudes to make clear that the fluxes of reference objects have been converted to the photometric system of the data that is being analyzed.

[psferguson]

Updated:

Loads the lsst.afw.table.SimpleCatalog reference catalog, computes ra and dec
(optionally) applying a proper motion correction. Also, color terms
are (optionally) applied to the reference magnitudes in order to transform
them to the data's photometric system.

returns a refCat with both the original loaded reference catalog and
the coorected coordinates (ra,dec) and transformed reference magnitudes
(refMag-/refMagErr-)

[bechtol]

Thanks. Looks great. Two very minor comments.

[edennihy]

No additional comments, nice work on clarifying the docstring

[psferguson]

Jenkins job -> https://ci.lsst.codes/blue/organizations/jenkins/stack-os-matrix/detail/stack-os-matrix/35671/pipeline