Fix Version/s: None
Sprint:Alert Production S17 - 3, Alert Production S17 - 4, Alert Production S17 - 5, Alert Production S17 - 6
The new matchPessimisticB matcher of
DM-8113 and DM-9750 has be tested on HSC visit 3358, an ultra dense stellar field, needs to be run on other visits from other cameras to verify that it works as intended in a wider variety of observing conditions and instruments. We will first run on a smaller test dataset from DECam and CFHT.
Validation of the final verified configuration will be carried out on separate tickets.
DM-10396 Run dataset for matcher validation
Visually verified the shift and rotation as measured by matchPessimisticB on visits from 3 different instruments: HSC (3358), DECam (406285, 410827), CFHT (793169, 896070, 980526). The matcher discovers the initial shift and rotation correctly for all ccds in these visits which represent a large range of density and distortion amounts.
With this ticket comes some minor improvements to the matching. A side effect of these updates is the code now passes unittests as they were written for matchOptimisticB without modification:
Use a iterative sigma clipped distance to cut matches and send them to the WCS fitter.
Use a least squares fit to the matched pattern between reference and sources with the shift/rotation implied by the first spoke of the pattern used as a the initial guess. The shift/rotation is forced to be approximately unitary in the fit so no requirement on the rotation matrix determinant is needed.
Small changes to match and fit loop. Now always tries to use pessimistic mode for first blind match. Once a match is found from a previous match/fit iteration it then uses optimistic mode.
Some ccds in the CFHT and DECam find the correct shift/rotation but end up with poor fits. This is usually caused by a star being matched to the incorrect star in a close pair of stars and is mainly a problem in fields were the source density is low (<100 per ccd). This can be solved by decreasing the signal to noise cut on sources and thus increasing their number. It could also be rectified by better outlier rejection in the fitter or by allowing for slight distortions in the shift/rotation matrix. These are left for future tickets.
Some changes requested.
One general question (also asked on github, but probably better answered here) is whether the new MatcherPessimisticSourceSelectorTask is really needed, or if the old MatcherSourceSelectorTask could use your updates instead. These look like useful improvements! I realize you may not want to risk breaking our existing code, but if it helps our current WCS fitting it might be worth the risk.
Responded to first round of comments on pull request meas_astrom/72 and meas_algorithms/80. Most changes adopted. Some questions asked in pull requests that may help direct the discussion.
Started running on DECam and CFHT visits.