Allow Ellipse2D and Sersic2D theta to be a quantity

[larrybradley]

Description

This PR allows the Ellipse2D and Sersic2D theta parameter to be input as an angular quantity. I'm calling this a new "feature" instead of a "bugfix" (but I can change that). Technically, there was nothing preventing quantity theta inputs, but the theta docstrings for Ellipse2D and Sersic2D only mention "float as radian". Also, for Ellipse2D a quantity theta would give the incorrect bounding_box (there was actually an Ellipse2D unit test for quantity theta, but it gives the wrong result). Sersic2D does not define a bounding_box, so angular theta works as expected, but was not documented.

Checklist for package maintainer(s)

This checklist is meant to remind the package maintainer(s) who will review this pull request of some common things to look for. This list is not exhaustive.

• Do the proposed changes actually accomplish desired goals?
• Do the proposed changes follow the Astropy coding guidelines?
• Are tests added/updated as required? If so, do they follow the Astropy testing guidelines?
• Are docs added/updated as required? If so, do they follow the Astropy documentation guidelines?
• Is rebase and/or squash necessary? If so, please provide the author with appropriate instructions. Also see "When to rebase and squash commits".
• Did the CI pass? If no, are the failures related? If you need to run daily and weekly cron jobs as part of the PR, please apply the Extra CI label.
• Is a change log needed? If yes, did the change log check pass? If no, add the no-changelog-entry-needed label. If this is a manual backport, use the skip-changelog-checks label unless special changelog handling is necessary.
• Is this a big PR that makes a "What's new?" entry worthwhile and if so, is (1) a "what's new" entry included in this PR and (2) the "whatsnew-needed" label applied?
• Is a milestone set? Milestone must be set but astropy-bot check might be missing; do not let the green checkmark fool you.
• At the time of adding the milestone, if the milestone set requires a backport to release branch(es), apply the appropriate backport-X.Y.x label(s) before merge.

[github-actions]

I'm the one who knocks!

(A special day message.)

[WilliamJamieson]

I only see one small changed to the tests (the fix for the bounding box test on Ellipse2D).

Can you add tests for Ellipse2D and Sersic2D with theta acting both as a "float as radian" and as a "angle quality"?

[larrybradley]

I've added unit tests.

[WilliamJamieson]

The tests look good for the most part. My final request is to add an evaluation comparison to each one (as I have suggested my comments). This way we know they models are consistent with each other and that they properly evaluate using both theta formulations.

[larrybradley]

Yes, that sounds good. I've added the model evaluation tests. Thanks!

[larrybradley]

The CI failures are unrelated and are coming from VOTable.

[pllim]

Looks related to me. You forgot to mark skipif?

        if cls._gammaincinv is None:
>           from scipy.special import gammaincinv
E           ModuleNotFoundError: No module named 'scipy'

.../astropy/modeling/functional_models.py:3087: ModuleNotFoundError

[larrybradley]

Thanks, @pllim . Indeed, Sersic2D requires scipy. I fixed the test.