Add warning when less than 2 data have WCS

[javerbukh]

Description

This pull request adds a warning message in the Links Control plugin when less than 2 no data in data collection has valid WCS.

EDIT:

I tried to support data deletion as well but noticed some bugs when deleting data in this PR. Please let me know if that is just on my end.

Change log entry

• Is a change log needed? If yes, is it added to CHANGES.rst? If you want to avoid merge conflicts,
  list the proposed change log here for review and add to CHANGES.rst before merge. If no, maintainer
  should add a no-changelog-entry-needed label.
• Add warning to Links Control plugin when less than 2 data have WCS.

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.

• Are two approvals required? Branch protection rule does not check for the second approval. If a second approval is not necessary, please apply the trivial label.
• Do the proposed changes actually accomplish desired goals? Also manually run the affected example notebooks, if necessary.
• Do the proposed changes follow the STScI Style Guides?
• Are tests added/updated as required? If so, do they follow the STScI Style Guides?
• Are docs added/updated as required? If so, do they follow the STScI Style Guides?
• Did the CI pass? If not, are the failures related?
• Is a milestone set? Set this to bugfix milestone if this is a bug fix and needs to be released ASAP; otherwise, set this to the next major release milestone.
• After merge, any internal documentations need updating (e.g., JIRA, Innerspace)?

[kecnry]

just a small performance-suggestion, otherwise looks good to me. We might want to tweak the language a bit if anyone finds it confusing, but that can be done as we review the larger PR.

[bmorris3]

Leaving some changes for future ease of reading/maintaining, and one point where I'm confused if it works.

[bmorris3]

Shouldn't this be

Suggested change

	if num_data_with_wcs:
	if num_data_with_wcs > 1:

[kecnry]

I don't think so, the increment happens below this line, so this is just saying if there was already one with WCS, making this the second entry, then enable linking and stop looping. But let's definitely add a comment that clears this up, I can see how it is confusing to read 😬

[javerbukh]

I added a comment explaining what is happening at this step, please let me know if that is sufficient!

[kecnry]

We should test this for the case of original rotation of a single image layer (which might be another motivation for eventually changing the name of the plugin... but that's out of scope here)

[javerbukh]

@kecnry Rotating a single image worked for me. Hopefully you both see the same thing!

[kecnry]

Nope, I'm seeing this with a single image layer in the app with WCS. It might be as simple as only requiring one (and then don't need the counter at all).

[javerbukh]

@kecnry So canvas rotation still works with only 1 data loaded into the viewer and if you try to link by wcs with 1 data, it looks like nothing happens. Should I revert the last commit?

[kecnry]

Canvas rotation will be removed soon (see #9)

I do see though that the linking itself fails and fallsback on pixel linking, but we need a way to still use the image rotation logic with only a single layer (that has valid WCS). @bmorris3 - can some logic be moved around so the default orientation is created immediately when requesting WCS-linking so that it can then link against that?

[bmorris3]

To make the single-data with WCS case work, we need to change this line:

jdaviz/jdaviz/configs/imviz/helper.py

Line 520 in 842c5d0

]) > 1

to be > 0 rather than > 1.