Add filter support for $id keys

[jfirebaugh]

mapbox/mapbox-gl-style-spec#391

Before merging, we need to following upstream changes to be integrated and released:

• geojson-vt: Add id feature property to tiles
• vector-tile-js: id should be a public property

[jfirebaugh]

@mcwhittemore brought to my attention the fact that once mapbox/geojson-vt#60 is integrated, we'll face an additional issue. For GeoJSON features that use string IDs, there's a GeoJSON/VT compatibility issue similar to #2434. GeoJSON allows string or numeric IDs, while VTs support only unsigned integer IDs. String values in GeoJSON feature IDs will not survive the round trip through a Vector Tile PBF which we use to transfer data from the worker to main thread.

[mourner]

@jfirebaugh could we replace the use of vt-pbf with geobuf? It supports the full GeoJSON spec and roundtrips exactly.

[jfirebaugh]

@mourner For GeoJSON sources, yes, we could use geobuf rather than vt-pbf.

Then the question is what do we do with vector tile sources?

1. Continue to use VT PBF format for transferring vector tile source data. Receiving end needs to deserialize in a different way depending on the source type.
2. Transfer vector tile source data with geobuf, and figure out some way to represent the necessary layer structure. (A VT is collection of layers, each containing a collection of features. GeoJSON itself -- and thus by extension geobuf, currently -- doesn't have a way to represent this, because FeatureCollections can't be nested.)

[mourner]

@jfirebaugh maybe transfer a flat feature collection, but also send a JSON of the structure? Maybe like this: {offsets: [0, 235, 1243124], layers: ['foo', 'bar', baz']}

[lucaswoj]

I am closing this PR because it has been inactive for a long time. The branch isn't going anywhere so please keep working on this feature and re-open the PR when it is ready!

Let me know if you have any questions.

[mourner]

I'm picking this up tomorrow.

[mourner]

@lucaswoj good to merge?

[lucaswoj]

@mourner Looks good to me!

[lucaswoj]

Related PRs / commits

• Add feature id support geojson-vt#70
• Make VectorTileFeature#id a public property vector-tile-js#46
• mapbox/feature-filter@019f1a0

[jfirebaugh]

Did #2888 (comment) (supporting non-numeric IDs) get solved, or is there an issue for the tail work there?

[jfirebaugh]

Ah, #2716 tracks the tail work.