Add a `relate` API?

[bretttully]

Summary

iOverlay provides some really cool stuff and I have been playing around with using it for some robust geometric ops. One thing that is missing, that would be awesome, is a relate API that returns the DE-9IM relationships.

Is this something you have thought about?

[NailxSharipov]

Full DE-9IM support is too complex.
However, some practical scenarios make sense like touches, within, and contains.

And perhaps add more flexible control over the overlay graph.
This way, anyone can implement the desired functionality.

[bretttully]

I had a little play around yesterday, I'll put up a pr with my idea.

[michaelkirk]

If you are looking for test cases, JTS has a great test suite of topological edge cases.

Look for "Relate" in https://github.com/locationtech/jts/tree/master/modules/tests/src/test/resources/testxml/general

We use many of these test cases to validate geo::Relate, but we use robust floating point calculations, so some of the answers likely diverge from iOverlay's expected output due to precision collapse.

Some of the JTS tests are annotated with precisionModel scale="1.0" rather than FLOATING, I think those might be more analogous to how iOverlay works, but I really don't know.