calc_error_radius is an overly complex and unnecessary calculation

askap-vast / vast-pipeline

This repository holds the code of the Radio Transient detection pipeline for the VAST project.

https://vast-survey.org/vast-pipeline/

MIT License

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calc_error_radius is an overly complex and unnecessary calculation #790

Open ddobie opened 4 days ago

ddobie commented 4 days ago

https://github.com/askap-vast/vast-pipeline/blob/328e7a5419e12eb13cb302b2cb92b96e1895dca2/vast_pipeline/image/utils.py#L43

From a discussion with @mauch: The function seems to be doing calculations that make sense if your uncertainties are in image coordinates, not celestial. The numbers it produces are not correct for celestial coordinates in general. The correct calculation should be much simpler - just take the max of the ra and dec errors

mauch commented 4 days ago

Actually, upon further thought after our discussion - I realised the equivalent calculation would be to take sqrt(ra_err^2 + dec_err^2) since the calc_error_radius function is computing the vertices of a box surrounding the error ellipse rather than the edges.