Details
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Type:
Bug
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Status: Done
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Resolution: Done
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Fix Version/s: None
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Component/s: meas_astrom
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Labels:None
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Story Points:4
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Epic Link:
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Sprint:Science Pipelines DM-S15-3
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Team:Alert Production
Description
The optimistic pattern matcher in meas_astrom, adapted from hscAstrom, does not check if reference objects have been used before when finding the reference object nearest to each source. As a result the same reference object may be matched to more than one source. This should not happen.
Attachments
Issue Links
- is contained by
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DM-2702 The new astrometry task gives poor results on CFHT data
- Done
Activity
I had a careful look at the code and I don't see any coding problem.
Regarding the algorithm itself ; if you have one reference object that could be matched to several sources, you seem to retain the fist match found and mark the reference as "used". Is it always the best choice ? Can we imagine that based on "some" criteria, the first match could be dropped and replaced by another one ?
Note that the algorithm is complicated and I may have missed something.
Dominique Boutigny
added a comment - I had a careful look at the code and I don't see any coding problem.
Regarding the algorithm itself ; if you have one reference object that could be matched to several sources, you seem to retain the fist match found and mark the reference as "used". Is it always the best choice ? Can we imagine that based on "some" criteria, the first match could be dropped and replaced by another one ?
Note that the algorithm is complicated and I may have missed something. Regarding picking the first match: I think it makes sense because sources and reference objects are sorted by decreasing brightness, so the brightest reference object is picked first to go with the brightest source. This is how the algorithm is described in "Fast algorithms for matching CCD images to a stellar catalogue" by Vello Tabur. It may be possible to be more clever, but I think it will suffice.
Note: I found errors in the doc strings in matchOptimisticB.cc suggesting that the catalogs were sorted by increasing brightness. I will correct those before merging.
Ok, it makes sense. So it's ok for me.
Dominique Boutigny
added a comment - Ok, it makes sense. So it's ok for me.
The work is in meas_astrom on tickets/
DM-2735I fixed the matching bug and updated the unit test accordingly.
I also took the liberty of making some cleanups in matchOptimisticB.