incorporate some kind of mask to account for bad/unusable regions for target selection

[moustakas]

Pasting from the thread [desi-targets 1068]:

@djschlegel suggests:

We may want to start a list someplace of regions of potential problems to be
looking at with each imaging data release.

We’ll likely need an object-based formalism to deal with some objects,
and pixel-based for others.  For example, for the large NGC galaxies
we may end up with a mask (circular or elliptical?) down to R25 for each.
Within that, we’ll want fiber locations chosen by some algorithm, perhaps
along the major + minor axes.  Anything within the SDSS footprint has
had its coordinates + other parameters fixed up by Mike Blanton for the
NASA-Sloan Atlas.  Or.. someone may argue that we should keep QSO selection
in NGC galaxies to use as backlights.

Could we start putting together a representative list of flavors of problem
areas and a specific example for each (hopefully already in our observed footprint).
— Bright stars
— Really, really bright stars like Vega
— L/T dwarfs that are bright in WISE and not in the optical images
— Andromeda — it’s in our footprint!
— NGC/UGC elliptical galaxies
— NGC/UGC spiral galaxies
— NGC/UGC irregular galaxies
— Abell clusters — for ex, what happens to Abell 370 and Abell 665
— Globular clusters (often in NGC/UGC)
— High stellar density near the Galactic plane; we get as close as |b| ~ 14 deg
— Cirrus emission, optical and/or infrared — Eddie or Aaron would have some suggestions
— Planetary nebulae — depending on our sky modeling, these can be particularly problematic
     (These are *also* a problem for the spectroscopy, as we’ve discovered in SDSS where
     we’ll get a bunch of best-fit redshifts at z=0 from the PN emission lines)
— Jupiter, Saturn, Uranus — we may want to just avoid this in the observing strategy, as we do for DECaLS

What other fun + wonderful regions am I missing?

[geordie666]

I'm planning on looking at this near-term (at least for bright stars)

[moustakas]

@geordie666 Can you briefly summarize what has been incorporated in terms of the bright-star mask (or point to where this was discussed previously -- I can't seem to find it)?

Related: The BGS WG is finding a large excess of sources in the small-scale angular correlation function (at 17<r<20) that we've tracked down to Messier/NGC-sized contaminants. See here, for example -- with many thanks to @ekitanidis for producing these. If we could incorporate even a basic Messier/NGC/UGC mask into our target selection code (or, alternatively, imaginglss), that would be very helpful.

[geordie666]

I think you're conflating two different bright star masks. The bright star mask to deal with large-scale structure is off-project. It would be a product of the science working groups. The bright star mask being built on-project (in the brightstar branch on desitarget https://github.com/desihub/desitarget/tree/brightstar) is to prevent saturation of adjacent fibers. If the goal of a mask is to remove potential LSS contaminants, then that would be a product of the science working groups. I believe Ashley Ross and the image validation working group or doing some work in that direction.

Note that there's no particular reason to apply masks for the purpose of science analyses a priori, other than to save some fibers in drastic cases. Such masks could be applied to targets after spectra have been taken in order to conduct science analyses. Such masks could, also, be applied in targeting, but then they'd have to be consistently applied again when studying, e.g., LSS. Whether to apply "science/LSS" masks during targeting or not is a decision for the science working groups.

On Fri, Jan 27, 2017 at 8:32 AM, John Moustakas notifications@github.com wrote:

@geordie666 https://github.com/geordie666 Can you briefly summarize what has been incorporated in terms of the bright-star mask (or point to where this was discussed previously -- I can't seem to find it)?

Related: The BGS WG is finding a large excess of sources in the small-scale angular correlation function (at 17<r<20) that we've tracked down to Messier/NGC-sized contaminants. See here https://desi.lbl.gov/trac/wiki/BrightGalaxyWG/TeleconNotes, for example -- with many thanks to @ekitanidis https://github.com/ekitanidis for producing these. If we could incorporate even a basic Messier/NGC/UGC mask into our target selection code (or, alternatively, imaginglss), that would be very helpful.

— You are receiving this because you were mentioned. Reply to this email directly, view it on GitHub https://github.com/desihub/desitarget/issues/41#issuecomment-275692828, or mute the thread https://github.com/notifications/unsubscribe-auth/ANTmRZiSc_j-XP_t1rNHDgrTn9HztLKvks5rWg39gaJpZM4H-ifb .

[moustakas]

A lot of progress has been made on this issue both on the imaging and the target selection side and I think we have a solid plan going forward. Closing this issue, which was more focused on discussion rather than a particular coding request.