Move GeoJSON normalization logic into core C lib about h3 HOT 6 CLOSED

@alexkokorin2 The basic algorithm looks like:

• Loop through all polygons
  • If the polygon winds counter-clockwise, it's an outer loop, put it into an array of outer loops
  • If the polygon winds clockwise, it's an inner loop (hole). Put it in a temp array of inner loops
• Loop through all inner loops
  • Take the first point.
  • Loop through all outer loops. If the point is inside the outer loop, allocate the hole to that polygon.
• Return the array of outer loops.

This doesn't deal with nested donuts, but otherwise should work. I'm going to be releasing a JavaScript GeoJSON lib shortly, and will probably include a JS version of this algorithm in that lib until this issue is resolved in the core library.

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@isaacbrodsky any update on this?

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Hi @alexkokorin2, the Javascript bindings that contain this logic have been released at uber/h3-js, but nobody's yet gotten to make a PR to include that logic here.

@nrabinowitz Now that I take another look at the h3-js sources, I actually don't see any hole detection code associated with h3SetToLinkedGeo / readMultiPolygon. Am I missing something, or could you point us towards the hole-detection logic?

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@isaacbrodsky Unfortunately the hole-detection logic is still in a closed-source library, as it was required for both the current H3 and the internal legacy version. I'd rather try to get it into C than to bring the JS version into the JS bindings. I expect to be able to work on this in the next 3-4 weeks, probably no sooner.

Implementation would be a lot easier if I could figure out a way to reuse the existing point-in-poly code. One option here is to convert GeoPolygon to LinkedGeoPolygon before running the algo, but this would sacrifice performance and memory usage for the code benefit. 😞

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@nrabinowitz Could you give me a hint/source how to create (at least) temporary fix for this? It appears my consumer isn't OK with your current format. I'd like to convert it to GeoJSON.

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@nrabinowitz @isaacbrodsky ping about temporary fix.

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