Allow full customisation of mapping spline interpolation

[ortk95]

307

Pull request checklist

• [x] Add a clear description of the change
• [x] Add any new tests needed
• [x] Run spell check on new text visible to user (documentation, GUI etc.)
• [ ] Check any changes to requirements.txt are reflected in setup.py
• [ ] Check code passes CI checks (run run_ci.sh or check GitHub Actions)

See CONTRIBUTING.md for more details.

[coveralls]

Pull Request Test Coverage Report for Build 6932262047

• 13 of 13 (100.0%) changed or added relevant lines in 2 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage increased (+0.002%) to 99.506%

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Totals
Change from base Build 6931068708:	0.002%
Covered Lines:	2785
Relevant Lines:	2799

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💛 - Coveralls