Support geobuf (geojson protobuf)

[jeroen]

See https://github.com/mapbox/geobuf

[sckott]

• good place if you want to make any geojson on a map http://geojson.io/
• geojson spec http://geojson.org/geojson-spec.html
• you can simply copy paste from the spec examples here http://geojson.org/geojson-spec.html#appendix-a-geometry-examples for small examples of each type
• us states as geojson https://github.com/glynnbird/usstatesgeojson
• there's an awesome geojson list https://github.com/tmcw/awesome-geojson

[jeroen]

Starting a new branch: https://github.com/jeroenooms/protolite/tree/geobuf

[jeroen]

Some notes from analyzing the @mourner JavaScript implementation:

• The uint32 dimensions = 2 field sets the size of a single point. Default is 2 (e.g lat+lon).
• Coordinate numbers are stored as (int64) y = x * 10^e where e is stored in precision. Hence 0.123 with default precision of 6 gets stored as 123000.
• The coords array contains the deltas of the coordinates by dimension. So [[100,20], [110, 5]] becomes 100,2,10,-15.
• Property keys are stored globally in repeated string keys and are referred by their index in custom_properties.
• Propery values are stored inside message Value: {oneof value_type}.
• For 3 deep structures, lengths stores size of each line. So [[[1,2], [3,4]], [[5,6],[3,3], [1,2]]] is stored as dimensions = 2 and lengths = 2,3 and coords = 1,2,2,2,2,2,-2,-3,-2,-1.

[jeroen]

@sckott I implemented the parser. Could you give this a try? To test, take an arbitrary geojson file and use the npm module to convert it to a proto buffer:

npm install geobuf
json2geobuf geojson.json > geobuf.pb

You can read geobuf.pb in R using protolite::unserialize_geobuf or protolite::geobuf2json.

[jeroen]

This is now fully implemented in protolite 1.4/