DESI target labelling: did some bits change?

[dstndstn]

From Eddie Schlafly:

Re viewer updates... here's the viewer and the viewer-dev for a patch of the sky:
http://legacysurvey.org/viewer-dev?ra=178.1051&dec=20.6939&zoom=16&layer=decals-dr7&targets-dr67
http://legacysurvey.org/viewer?ra=178.1051&dec=20.6939&zoom=16&layer=decals-dr7&targets-dr67
does the center source lose its label for some reason?

[dstndstn]

Hey @geordie666 , were there any changes to the targeting bits that might cause this?

"viewer" is using dr7.1-0.23.0
"viewer-dev" is using dr7.1-0.29.0

[dstndstn]

I think the changes that @ziyaointl made were purely CSS, so wouldn't affect whether a target had a label...?

[geordie666]

This is caused by how desitarget resolves targets with a view towards DR8. The default is now to resolve targets (RESOLVE = T in the header of the target files).

For resolved targets, the primary bits ELG, LRG, QSO... are only set, for objects from DECaLS photometry, if they pass the "southern" (DECaLS-appropriate) targeting algorithms. The particular target you highlight passes the "northern" cuts but its provenance is from the "southern" imaging. It therefore has ELG_NORTH set but not ELG.

At some point (I'm guessing) displaying the NORTH/SOUTH labels in the viewer was deprecated to avoid label-clutter, so no label is included for this object.

Python dump:

from desitarget.io import read_targets_in_cap
from desitarget.targetmask import desi_mask
targ = read_targets_in_cap("0.29.0/main", [178.1049, 20.6961, 1./3600], columns=["DESI_TARGET"])
desi_mask.names(targ["DESI_TARGET"])
Out[]: ['ELG_NORTH']

Lots of context in desihub/desitarget#426 with more discussion in desihub/fiberassign#193. Mark (working with @sbailey) also recently independently discovered this (see [decam-data 3396]).

[dstndstn]

Thanks, @geordie666 !

@ziyaointl , would you be willing to change the server-side code that does the labeling -- in map/cats.py function desitarget_color_names? I think what we want is to only set ELG_NORTH, ELG_SOUTH, etc, if ELG is not set? Otherwise, every ELG will be labelled "ELG, ELG_NORTH", which is going to clutter things.

[ziyaointl]

@dstndstn Sure! I will get started this week