We have been developing an obs package to process VISTA imaging with the LSST stack. A big question for us has been whether to ingest the community 6 exposure stacks (ISR already performed, deep enough to get good photocal matches and measure ‘PSF’) or the direct exposures (harder to measure PSF because of depth but measurement done as expected by the stack on single exposures, requires a lot of effort to rewrite ISR etc). We have been told that if we use the stacks then we need to ingest the variance images made by the VISTA (Cambridge Astronomical Survey Unit - CASU) pipeline. I have therefore been looking at the ‘instcal’ ingestion and nullISR task in obs_decam.
I can see how the variance and masks are being ingested but as far as I can see the nullIsr task simply puts the ISR ‘instcal’ images after the ISR stage. I don’t see how it is propagating the ‘wtmap’ which has been ingested. What our obs package is currently doing is simply pretending the stacks are exposures and letting it estimate the variance image. Is there a different processCcd task developed somewhere other than the main GitHub repo?
What has been the general experience with the obs_decam and instcal images? Would those with experience recommend using the community pipeline images or is it always better to use the LSST exactly as designed on raw images. Could I see a full example of running the pipeline with instcal images?
Many thanks for everyone’s help over various questions,