Bugfix shape masking

[hsteptoe]

🚀 Pull Request

Description

Fixes #6126 by exposing the shape geometry to the user. Adds to docs and docstrings to make it clearer how to use this.

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[pp-mo]

From @SciTools/peloton : discussed what we are seeing here and in #6126.
We think this is looking useful, but the two of you seem to have it covered @hsteptoe @acchamber ?
Please shout if you need help.

[hsteptoe]

Discussion with @acchamber notes:

• Don't move imports out of functions as this creates circular import errors
• Check target_crs assignment for occasion when cube doesn't have a CRS
• Re-write conversion of 0-360 -> -180-180 coords in case of degree based CRSs

[hsteptoe]

What are @SciTools/peloton (@pp-mo) thoughts about adding rasterio as a Iris dependency?

This would facilitate better handling of shapes to rasters (which is essentially the problem we're solving) with the added bonus that we could also mask to other shape types, like lines, to extract a trajectory from a Cube, for example.

[acchamber]

I've had a few other discussions with other users now where they can't use this function with OSGB shapefiles which this PR would fix. Where are we on being able to include it in the next release?

@hsteptoe @pp-mo

[hsteptoe]

I've had a few other discussions with other users now where they can't use this function with OSGB shapefiles which this PR would fix. Where are we on being able to include it in the next release?

@hsteptoe @pp-mo

I was planning on going to the AVD surgery this week to discuss some changes and/or make the case for rasterio

[trexfeathers]

Thanks for your patience everyone. It's sometimes a struggle to balance everything and we just haven't had an opportunity to discuss this. Coming to the Surgery (UK Met Office) is an ideal next step.

[stephenworsley]

@pp-mo, @trexfeathers and @stephenworsley have discussed this at the Surgery and agree in principle that we could consider adding rasterio as an optional dependency.