Nearly all many-visit HSC datasets that I've tried to process fail to fit photometry because the chi2 starts out as NaN, resulting in all stars being rejected as outliers and (after a long time) Eigen blowing up. We can't proceed with the photometric part of the meas_mosaic comparison until I can produce a fit.
Some steps to try:
- make jointcal fail immediately if chi2 is NaN (write a testcase for this)
- fit the SimplePhotometryModel instead, to see if that doesn't produce NaN
- print various input values to look for NaNs
- Is it worth writing the astrometry output before starting the photometry fit, so we at least have it in case of failure?