[geos-devel] Intersection result ordering change between 3.7.1 and 3.9.0

Paul Ramsey pramsey at cleverelephant.ca
Wed Jan 6 17:36:13 PST 2021

> On Jan 6, 2021, at 5:31 PM, Andrew Hershberger <andrew.d.hershberger at gmail.com> wrote:
> A GEOSwift consumer noticed some differences in intersection behavior between geos 3.7.1 and 3.9.0. I'm guessing this is related to OverlayNG? https://github.com/GEOSwift/GEOSwift/issues/212

Yes, component ordering in collections, ring start/end points, interior ring ordering, it's all potentially changed in 3.9 with the NG overlay. You can retain tests that work across new/old versions by applying the GEOSNormalize() function to everything, to get a deterministic ordering of rings/components/start points etc.

> I'm looking for guidance on how to advise them w.r.t. their statement that they're relying on "the order of the intersection points". Is that part of the contract such that changes should be considered breaking?

Not sure what that means, maybe they are intersecting lines and getting points? Would need to know the precise use case to know if it's something we used to try and preserve.


> Andrew
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