Implement Polygon.Intersection

[ctessum]

Since it seems acceptable to use this space to indicate interest in specific features, I would like to request polygon intersections. The Go language currently lacks a high quality library for boolean operations on geographic features, and having one would help me out greatly. (I am one of the maintainers of a low-to-medium quality library.) I greatly appreciate all the work that has happened so far to port this library to Go.

[dsymonds]

Yep, it is totally acceptable. ;-)

e7cfa0c added Polygon.Contains and Polygon.Intersects. To clarify, you're after the equivalent of C++'s S2Polygon::InitToIntersection?

[ctessum]

Yes, I mean the equivalent of S2Polygon::InitToIntersection. Thanks!

[brendanashworth]

I'm interested in contributing a PR for this — are there any thoughts on using Martinez-Rueda for the boolean operation algorithm? Or would it be best to port the C++ version accordingly?

[ctessum]

There is a port of (one of) the Martinez-Rueda algorithms here. However, that one is for planar geometry, not sure that it would work here?

[brendanashworth]

@ctessum I'm not sure myself. The projection onto a plane would conserve intersection points but not lengths.. is it naive to assume the lengths are proportional and thus area is conserved after we project back to the sphere?

[alphairys]

any update on this? Curious if anyone is actively working on this piece?

[brendanashworth]

@alphairys I don't have an update/I haven't been working on it. If you're looking for a workaround, I've been using CellUnions (after covering the polygon with cells) as a workaround, and they implement simple binary operations like CellUnionFromIntersection.

[rsned]

There is still work being done on this

[ipipdotnet]

I think someone has already done that https://github.com/davidreynolds/gos2/blob/master/s2/polygon_test.go