Ugrid save

[pp-mo]

🚀 Pull Request

Description

Support for saving cubes with meshes.
(No "save_mesh" yet, easy to add that later)

Current status :

Good for review.

Some additional questions to consider ..

• should we minimise the number of small/bounds dimensions created ? See this comment
• should we be augmenting the global 'Conventions' attribute See this comment
• should the cube-summary changes be pulled out into a separate PR ?

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Consult Iris pull request check list

[pp-mo]

General question : should we be adding some kind of UGRID reference to the global 'Conventions' attribute ?

• Iris currently just uses Conventions = "CF=1.7" : see here and here
• LFRic/XIOS output files currently have Conventions = "UGRID" : see here
• in pure netcdf terms, we can apparently have "CF UGRID", but there is no special mention of of meaning for versions : See here
• there is no particular agreement within either CF or UGRID for how to do this, or refer to the other
  • i.e. does "UGRID" imply CF ? That doesn't seem to work as the versions are explicitly connected (at least yet)
  • there is discussion here but no clear winning solution yet

[bjlittle]

@pp-mo Over to you. It's looking good, considering what you inherited 😉

A few review comments to service, but nothing major. I've still to sweep through the tests, so I'll do that in the meantime.

[pp-mo]

Ok, that was a useful stage to review both the existing code + my changes.
Some more tweaks, now feeling more confident.
@bjlittle I hope this addressed everything raised so far (but I pushed back on a couple) : please re-review

[bjlittle]

@pp-mo Truly super stuff, thanks 🎉

[trexfeathers]

I have 105 email notifications about this - you two must have worked really hard! 🏆🏆