Switch to martinez clipper

[bhousel]

Ok, so this is promising. It's fast and small, but I am running into some of the unioning issues reported in the martinez repo:

JSTS/Turf

Martinez

I have a feeling w8r/martinez#115 might fix this, so I'm going to leave this work on a branch and wait for martinez to get an update. It's great to see that there is active work being done!

[quincylvania]

Simply the best feeling:

[bhousel]

I updated this branch to have the latest code from master as well as updating martinez-polygon-clipping to 0.7.0, but still seeing some artifacts. I'm not surprised, as there are open issues upstream for things like this..

[quincylvania]

@bhousel Are there tweaks we could make to the data to work around the martinez bugs? Things to avoid? I'd be happy to sacrifice some space efficiency in order to drop JSTS.

[bhousel]

@bhousel Are there tweaks we could make to the data to work around the martinez bugs? Things to avoid? I'd be happy to sacrifice some space efficiency in order to drop JSTS.

I don't think so.. We can probably always invent situations where the country coder geometries will intersect this way.

It looks like w8r/martinez#115 didn't actually merge yet, and there are some related issues in the comment thread that it would also fix, so I wonder if I could spend time on that to finish it up..

[bhousel]

I dug in a bit more today and learned a few things.

The clipping might be ok. The rendering artifacts are probably caused by a mapbox-gl / earcut issue

• GeoJSON polygon rendering is unreliable (master ticket) mapbox/mapbox-gl-js#7023

The locationSet that I'm testing is:
{ include: ['039', '015'] }

This is the "Southern Europe + Northern Africa" example:
https://ideditor.github.io/location-conflation/?locationSet=%7B%20include%3A%20%5B%27039%27%2C%20%27015%27%5D%20%7D

The region around the Canary Islands does this:

But it looks fine on https://geojson.io:

So I reduced it to this simpler test case:

{
  "type": "Feature",
  "properties": {},
  "geometry": {
    "type": "MultiPolygon",
    "coordinates": [
      [
        [
          [-15, 40],
          [-15.92339, 29.50503],
          [-8, 32],
          [-7.37282, 36.96896],
          [-15.92339, 29.50503],
          [-25.3475, 27.87574],
          [-17.27295, 21.93519],
          [5.14112, 40],
          [-15, 40]
        ]
      ]
    ]
  }
}

Geojson.io:

Mapbox GL 1.8:

Some more things I want to try

• Run the result through geojson-rewind ?
• Do the clipping with integers only (no floating point). I wrote this code today and it's working ok. It's kind of hacky but if it helps I'll leave it in, if not I'll throw it out.

[bhousel]

ok it's definitely a bad clipping result and not the result of improper winding.

Going to also check out this other alternative library: https://github.com/mfogel/polygon-clipping

[bhousel]

superseded by #20