I'm guessing this originates in DM-8210, where, on 448121a4, the copyColumns config which included coord_ra and coord_dec was removed as a duplicate. We do still have a copyColumns in ForcedMeasurementConfig, but it doesn't mention these fields.

Reading DM-8210, I'm confused about what's actually supposed to be going on here. Jim Bosch, maybe you could clarify the intention?

I think I was assuming that the forced photometry tasks would explicitly set the coord fields from the reference catalog, but it appears that's not the case - reference catalog centroids are now added to the forced catalogs via the base_TransformedCentroid plugins in meas_base, which basically act like a centroiding algorithm that just looks up the coord fields from the reference catalog and copies it into the centroid fields in the forced catalog. It appears that in the past we were actually relying on copyColumns to do that.

So, one way to fix this would be to just add these to copyColumns in the ForcedMeasurementTask config defaults. Another would be to add a forced-measurement version of the base_SkyCoord algorithm in meas_base, which is what we use in single-frame measurement to fill the coord fields. Or it might be best to have base_TransformedCentroid do that itself; I can't think of a reason why it shouldn't. I think any of these is fine - they're all a bit ugly, IMO, and maybe copyColumns is worst just because it can lead to the kinds of problems we saw in DM-8210 if we use it to overwrite existing columns - but the ultimate reason this is difficutl is because I think it's intrinsically tricky (but of course incredibly useful) to have the coord columns at all in what is otherwise a table containing only raw, uncalibrated quantities.

Thanks Jim!

Do we care about deblend_nchild? It looks to have been dropped in the same commit as the RA/dec.

I think that was correctly dropped - there is no deblending on CCD-level forced photometry right now, so I think that field would be more misleading than helpful.

Ummm...I care! I've been reading it in from the meas catalogs. They also have a few other fields I've been using that don't get persisted/copied to the forced cats, so I may not be able to avoid reading in both for my current use case, but it would be nice to have (assuming there's no fundamental reason to leave it out that I'm missing).

Please make sure that Lauren MacArthur agrees with the decision not to restore deblend_nchild before you merge.

I would really like it in the coadd forced catalogs (where deblending is done, correct?)

Revised:

-price@pap-laptop:~/LSST/meas_base (tickets/DM-9556=) $ git sub-patch

commit 94f876db450f3494ff1ef8d737c696a4586f7836

Author: Paul Price <price@astro.princeton.edu>

Date:   Fri Mar 31 11:48:21 2017 -0400

    forcedMeasurement: copy coordinates, deblend_nChild

    Forced measurement catalogs currently have no RA,Dec or

    deblend_nChild. These used to be copied from the reference

    catalog, but commit 448121a4 removed this behaviour.

    Restoring it.

diff --git a/python/lsst/meas/base/forcedMeasurement.py b/python/lsst/meas/base/forcedMeasurement.py

index 52dcbb3..1c97858 100644

--- a/python/lsst/meas/base/forcedMeasurement.py

+++ b/python/lsst/meas/base/forcedMeasurement.py

@@ -163,7 +163,8 @@ class ForcedMeasurementConfig(BaseMeasurementConfig):

     copyColumns = lsst.pex.config.DictField(

         keytype=str, itemtype=str, doc="Mapping of reference columns to source columns",

-        default={"id": "objectId", "parent": "parentObjectId"}

+        default={"id": "objectId", "parent": "parentObjectId", "deblend_nChild": "deblend_nChild",

+                 "coord_ra": "coord_ra", "coord_dec": "coord_dec"}

     )

     checkUnitsParseStrict = lsst.pex.config.Field(

Also need:

price@pap-laptop:~/LSST/meas_modelfit (tickets/DM-9556=) $ git sub

commit f2c37e1e4543ce5b5ffe670d2c149d8c426ca6b9

Author: Paul Price <price@astro.princeton.edu>

Date:   Fri Mar 31 13:35:24 2017 -0400

    tests: adapt to ForcedMeasurementConfig changes

    ForcedMeasurementConfig now by default copies fields that aren't

    present in our basic test catalogs, so set the list of columns

    to copy to what we do have (the same setting as was default previously).

 tests/testDoubleShapeletPsfApprox.py         | 1 +

 tests/testGeneralShapeletPsfApproxPlugins.py | 1 +

 2 files changed, 2 insertions(+)

Plus similar changes in meas_extensions_photometryKron.

Jim Bosch, there are four new changes to review, required in tests of forced measurement because we changed the defaults to require a field which isn't present without some extra effort. Changes are in meas_modelfit, meas_extensions_photometryKron, meas_extensions_convolved and pipe_tasks. They're pretty simple, but please have a quick look at them before I merge.

Looks fine. Too bad it's so fragile, but I don't see a simple way to fix that, and it's certainly out of scope here.

Thanks Jim.

Merged to master.