Refactor wcsmod module into individual modules for each wrapper

[ejeschke]

• puts each WCS wrapper in a separate module
• for easier administration and editing

[pllim]

I think __init__.py needs some extra imports into the ginga.util.wcsmod namespace to make it backward-compatible.

[ejeschke]

I was wondering about that. But I didn't find any grepping through the Ginga source code or testing so far. Are there some STScI plugins that are importing things that are not present in this version?

[pllim]

Are there some STScI plugins that are importing things that are not present in this version?

Not that I can grep but STScI is not the only user of Ginga. What about SunPy etc?

[ejeschke]

@pllim, from what I can tell, the only "interesting" imports from wcsmod were "WCS", "display_types", "coord_types" and "use". These are all preserved. The only other thing of interest might be if someone wanted to import one of the WCS wrapper classes directly. But there is no place in Ginga that does that, and we don't in any of our Subaru plugins. Sounds like STScI doesn't either. I don't think that would be likely for any end users either--they would be using the native WCS, not the wrapper. So I think we are ok here, actually, so long as these four are preserved.

[pllim]

I briefly did import one of the wrapper classes directly for #495 but then undid it as part of your reviews. Therefore, I am satisfied by your explanation above.

[ejeschke]

Ginga has unit tests for wcsmod, and these pass with the PR.

[ejeschke]

One thing I am thinking about (and I guess I will leave it for a future PR) is to refactor pixtoradec, radectopix and pixtosystem to just be wrappers around the vectorized versions that you created.

[ejeschke]

Another thing that this PR does is open the door for using different WCS packages with different images. So for example, you could have a "gwcs" wrapper for some images and "astropy" for some others. You can imagine other possibilities. Pretty straightforward with the changes made here.

[ejeschke]

Merging.

[ejeschke]

Oh, you might need to remove wcsmod.pyc or other cached versions in order to avoid accidentally importing the old module.

[pllim]

Yes, this would be useful for #327 and #434.