Proof of concept: MeshIndexSet

[stephenworsley]

🚀 Pull Request

Description

Implements a possible way to subset a Mesh while retaining a reference to the original Mesh. A MeshIndexSet would be effectively an implementation of the UGRID concept of a location index set. This particular implementation has the benefit of appearing like a regular mesh for most opperations and is capable of functioning with iris-esmf-regrid, for example. The benefit of such a set over a strictly smaller Mesh is that it opens the option for introducing sophisticated functions which can "stitch" a collection of MeshIndexSets back together into their original Mesh. One use case which this may be useful in is when calling expensive functions, like in iris-esmf-regrid, which a full Mesh would be too large to process as a whole so it must be processed as a series of submeshes. It may well be that such cases are specific enough that it is better to solve each on their own terms, but if such problems are general enough, there may be a case to introduce a class like this one.

[codecov]

Codecov Report

Attention: Patch coverage is 25.47771% with 117 lines in your changes missing coverage. Please review.

Project coverage is 89.35%. Comparing base (e92e36a) to head (7c05019).
Report is 5 commits behind head on main.

Files	Patch %	Lines
lib/iris/experimental/ugrid/mesh.py	25.47%	117 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #6014      +/-   ##
==========================================
- Coverage   89.75%   89.35%   -0.41%     
==========================================
  Files          90       90              
  Lines       22929    23102     +173     
  Branches     5020     5062      +42     
==========================================
+ Hits        20580    20642      +62     
- Misses       1618     1729     +111     
  Partials      731      731              

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.