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Move position_angle() from SkyCoord to BaseCoordinateFrame #15737

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merged 2 commits into from Dec 15, 2023
Merged

Move position_angle() from SkyCoord to BaseCoordinateFrame #15737

merged 2 commits into from Dec 15, 2023

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eerovaher
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Description

The first commit implements a new private method in BaseCoordinateFrame that simplifies the implementation of separation() and position_angle() methods.

The second commit moves position_angle() from SkyCoord to BaseCoordinateFrame. The method remains accessible for SkyCoord instances because they have access to methods defined both in SkyCoord and in their underlying frame.

I felt it appropriate to create a new file for testing methods that are implemented in BaseCoordinateFrame, but are exposed also by SkyCoord instances. That file should also include tests for separation() and separation_3d(), but moving those tests over would be beyond the scope of this pull request, which is large enough as it is.

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@eerovaher
Simplify computing coordinate differences on sky
00fd187 
`BaseCoordinateFrame.separation()` and `SkyCoord.position_angle()`
perform many analogous computations, which are now implemented in
`BaseCoordinateFrame._prepare_unit_sphere_coords()`. This seems to lose
some error handling in `SkyCoord.position_angle()`, but the errors that
were meant to be caught there cannot be triggered.
@eerovaher eerovaher added this to the v6.1.0 milestone Dec 14, 2023
@eerovaher eerovaher requested a review from mhvk December 14, 2023 19:52
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pllim
pllim reviewed Dec 14, 2023
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docs/changes/coordinates/15737.feature.rst Outdated
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Isn't this more like api?

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Previously BaseCoordinateFrame had no position_angle() method, but now it does. That looks like a new feature to me.

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But... you are moving it from another class. @mhvk , what say you?

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I think from the user-perspective, there is no change of API for SkyCoord -- it is more like a refactoring -- while there now is a new feature on BaseFrame, so I think "enhancement" is most appropriate.

mhvk
mhvk approved these changes Dec 14, 2023
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Thanks! A nice little improvement, making things more logical.

I also like the new test file. Will you be doing a follow-up PR to move the separation methods?

astropy/coordinates/baseframe.py Outdated
-------
`~astropy.coordinates.Angle`
The (positive) position angle of the vector pointing from ``self``
to ``other``. If either ``self`` or ``other`` contain arrays, this
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let's add ", measured East from North" to give people new to position angles a clue as to what to expect (though the examples help!)

astropy/coordinates/baseframe.py Outdated
>>> c2.position_angle(c1).degree
270.0
"""
from .angles import position_angle
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Can this be on top? Or does it cause a circular import?

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There's a few functions here that import things locally and it would be good to have a separate pull request to clean them up. I thought this line could be included in that, but this line does not exist in this file before this pull request, so we can indeed avoid some code churn by having a module level import in this pull request already.

astropy/coordinates/baseframe.py Show resolved Hide resolved
@eerovaher
Implement BaseCoordinateFrame.position_angle()
421a476 
The `position_angle()` method has been moved form `SkyCoord` to
`BaseCoordinateFrame`. The method is still accesible to `SkyCoord`
instances because they expose methods of their underlying frames.
@eerovaher
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@mhvk asked:

I also like the new test file. Will you be doing a follow-up PR to move the separation methods?

I am planning to look at the relevant tests, and not just for the separation methods but for position angle too. For example, it is not clear to me if the tests in test_sky_coord_velocities.py are worth keeping:

astropy/astropy/coordinates/tests/test_sky_coord_velocities.py

Lines 236 to 237 in f87e75d

def test_position_angle(sc, sc_for_sep):
sc.position_angle(sc_for_sep)

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mhvk commented Dec 15, 2023

Thanks! Let's get it in.

@mhvk mhvk merged commit 586a144 into astropy:main Dec 15, 2023
29 of 32 checks passed
@eerovaher eerovaher deleted the unify-sep-pos-angle branch December 15, 2023 16:09
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@mhvk mhvk mhvk approved these changes

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@eerovaher @mhvk @pllim