Heads up for DC2

[humnaawan]

As the analysis for DC1 begins and efforts for DC2 ramp up, I wanted to report a few results. We tried finding the DC1 chip list using a different method as a cross-check; thanks to @danielsf. Comparing the numbers, we find that the other method produces 8434 more chips overall (~4.5% of the simulated DC1 science sensors) but misses some that are produced in the current list. Looking at the exact positions, the chips that are missing in one dataset and present in the other either lie at the boundary of the DC1 region or are (almost) outside the nominal circular FOV, e.g., see this short simulation for some examples:

It isn’t clear if there’s a quick solution to the problem as the high HEALPix resolution to find the chips causes some pixels near the boundaries (FOV’s or DC1 region) to be deemed outside the visit, hence missing some chips (that are on the relevant raft and/or are in the region). While the impacts of these missing visits should be negligible for DC1**, we might need to think about a clever way to find all the chips that need to be simulated for DC2. Of course, a metric to estimate the expected number of chips (as was suggested in one of the SSim telecons) would help check whether the chip-finding technique is effective.

**If the missing chips were uniformly within the FOV region (which they are not and hence are not that critical), the 4.5% missing sensors would translate to a loss of about 0.02mag in differential depth.

[cwwalter]

Thanks @humnaawan! It seems to me that, a certain point, doing the chip removal won't be really justified since the number of chips on the edges of the region will become fractionally non-important and won't really change the CPU/storage requirements substantially.

At 300sq we would have ~31 undithered visit locations. Would there still be a substantial effect in this case?

[cwwalter]

@humnaawan and @egawiser Just following up/triaging some old issues: Would it be straightforward to make an estimate for the question I asked in the last comment? Specifically, is it worth doing this sort of trimming for DC2 or is that already large enough that the extra sensor simulation is fractionally unimportant?

[cwwalter]

This issue was moved to LSSTDESC/DC2_Repo#5