Consider this example:

A is the outer ring. B and C are inner rings. With your Polygon Area algorithm, we'll calculate Area(A) - Area(B) - Area(C), which is different than calculating the green area in the image.

I wonder if there are other libraries that handle this scenario.

A natural response would be "this is an invalid Polygon since the inner rings fall outside the outer ring". I think this is a valid response for the time being unless someone knows of an easy way to do the correct calculation above.

@zarch What do you think? I think your changes are an improvement and I'm 👍 on merging them. Just want to pass this by you. Thanks for the pull request!

Your polygons are invalid according to the "Simple Features" specification from the OGC.

Also according to the GeoJSON spec, although that's much less rigorously defined: http://geojson.org/geojson-spec.html#polygon

Thanks for your input @waywardmonkeys, much appreciated!

This pull request looks good to me. @zarch Feel free to merge and deploy a new version (0.2.1). Otherwise I can do it myself sometime tomorrow. 🎊

Thank you @frewsxcv, in these days I was think that would be nice to add a trait like: IsValid (is_valid) that check if a geometry is valid or not.
I'm wondering if this check should be implemented in the rust-geo library or in an external one (rust-geo-validation? where is the right place to raise question on the georust ecosystem and structure?).
I think the validation should use different validation-driver (e.g. geos, grass gis, etc), and would be nice to have also function to fix the input (e.g. converting your example into a multipolygon).

in these days I was think that would be nice to add a trait like: IsValid (is_valid) that check if a geometry is valid or not. I'm wondering if this check should be implemented in the rust-geo library or in an external one (rust-geo-validation? where is the right place to raise question on the georust ecosystem and structure?).

For now, I think opening a new issue in this repository (rust-geo) should be fine for now.

I also just created https://github.com/georust/meta/ as a place to discuss GeoRust projects and the organization.