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• jointcal shall be runnable as a command-line Task that takes the src and ref_cat datasets as input and produces (at least) a wcs and photoCalib dataset as outputs, which provide updated astrometric and photometric calibrations.
• jointcal shall perform a different fit for each tract, and allow multiple tracts to be run in single invocation (at least in serial, which is all meas_mosaic does).  Some visits may thus be processed with multiple tracts.   RHL:  Is the "different fit for each tract" a comment on how meas_mosaic does things?  It's not the correct behaviour for jointcal as many things (e.g. the camera model, the atmospheric models) will be continuous across tract boundaries.   Some things won't be, of course, including the PSF models and thus the centroids.
• jointcal shall fit models that have a level of sophistication similar to those in meas_mosaic (if it fits simpler models, it will be because the tests below demonstrate that they are sufficient to generate similar-quality results).  That involves:
  • astrometry: a full-focal-plane polynomial transform for each visit composed with a rotation and translation for each CCD (which is the same for all visits in the fit).
  • photometry: a full-focal-plane polynomial scaling for each visit multiplied by a constant scaling for each CCD (which is the same for all visits in the fit) and the determinant of the Jacobian of the astrometric model.

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• AM1, AF1 (astrometric accuracy and outlier fraction on 5 arcmin scales).
• AM2, AF2 (astrometric accuracy and outlier fraction on 20 arcmin scales).
• Median astrometric RMS (left plot of validate_drp's check_astrometry plot).
• PA1 (astrometric accuracy).
• Median photometric RMS for SNR>100 (upper-left plot of validate_drp's check_photometry plot).

RHL: why are we computing metrics rather than directly comparing the solutions and calculating metrics on the differences?  I'm worried that these KPMs are rather a blunt instrument to find regressions – in fact, any regressions that we find will indicate new metrics to calculate. 

No significant difference is a bit tricky to define here because most of these metrics are not accompanied by uncertainty estimates; to estimate them we'll use the RMS of the meas_mosaic metric (henceforth σ) results over different tracts of HSC Wide.  Differences less than 0.1 mmag for photometry or 0.1 mas for astrometry (even if larger than the cross-tract RMS, though I doubt the RMS across tracts will be that small) can also be ignored.

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