Fix how coordinates handles negative or nan parallaxes/distances #7988
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Hi there @adrn 👋 - thanks for the pull request! I'm just a friendly 🤖 that checks for issues related to the changelog and making sure that this pull request is milestoned and labeled correctly. This is mainly intended for the maintainers, so if you are not a maintainer you can ignore this, and a maintainer will let you know if any action is required on your part 😃. Everything looks good from my point of view! 👍 If there are any issues with this message, please report them here. |
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Failures are real! Apparently, in master, you can do: >>> rep = coord.SphericalRepresentation(160*u.deg, 10*u.deg, 10*u.pc)
>>> -rep
<SphericalRepresentation (lon, lat, distance) in (deg, deg, pc)
( 160., 10., -10.)>Because of this change, that no longer works: >>> rep = coord.SphericalRepresentation(160*u.deg, 10*u.deg, 10*u.pc)
>>> -rep
NotImplementedI actually feel like the behavior in this PR is more "correct", in the sense that a negative distance doesn't mean anything, so we might want to either not allow this operation (i.e. raise a |
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I think I prefer the "special-casing" option, @adrn. That's actually more consistent with what representations do anyway, right? |
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Well, kind of. For any Representation object, it uses |
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I think we need to keep |
| "distances even when `allow_negative=True`, " | ||
| "because negative parallaxes cannot be transformed " | ||
| "into distances. See discussion in this paper: " | ||
| "https://arxiv.org/abs/1507.02105", AstropyWarning) |
astropy/coordinates/distances.py
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| "https://arxiv.org/abs/1507.02105", AstropyWarning) | ||
| else: | ||
| raise ValueError("Negative parallaxes are not " | ||
| "interpretable as distances. If you " |
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Add the citation to the paper here too, perhaps?
| self._distance = self._distance.view(Distance) | ||
| try: | ||
| self._distance = Distance(self._distance, copy=False) | ||
| except ValueError: |
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There may be other sources of ValueError here. Easiest thing to do is just check that the message mentions the distance being >=0...?
This addresses a few issues related to how negative parallaxes / distances are handled in coordinates.
with master:
with this PR:
Fixes #7408