h3.h3SetToMultiPolygon - Confusing return values about h3-js

[nrabinowitz]

The issue here has nothing to do with H3, but rather the way you are constructing the polygons for Google maps. Is there no way to simply use GeoJSON input?

If I understand your code correctly, you are assuming all polygon loops are outer loops. They are not - only the first polygon loop is an outer loop. Subsequent loops are holes (this is following the GeoJSON spec). So what you're seeing is that holes in your polygon are being shown as filled polygons, rather than being excluded. I don't know how to exclude holes in the Google maps framework you're using - I'll leave it as an exercise for the reader :).

[chris-eaton]

Thanks for your pointers - I have it working now.

If it always returns a GeoJSON object why allow a flag to be passed into the function?

[chris-eaton]

To help anyone else who finds this question here is the code to make this work:

        var megaPolygon = h3.h3SetToMultiPolygon(h3StringArray, true);

        var data = {
            type: "FeatureCollection",
            features: [{
                "type": "Feature",
                geometry: {
                    "type": "MultiPolygon",
                    "coordinates": megaPolygon
                }
            }]
        };

        this.mapObject.data.addGeoJson(data);```

[nrabinowitz]

If it always returns a GeoJSON object why allow a flag to be passed into the function?

By default, the C library returns polygons with lat,lng points and without repeating the first point as the last point. The flag switches this to lng,lat points and closes loops by repeating the first point at the end, per the GeoJSON spec.