Concatenate pbf tiles and TileJSONs

[petrsloup]

We need to be able to process following requests:

• /vector/{mbtiles_name},{mbtiles_name}/{z}/{x}/{y}.pbf
  • the pbfs need to be concatenated (we already do this for fonts)
  • the issue is with concatenating pbfs from different zoom levels
    • e.g. /vector/a,b/8/19/21.pbf when b has maxzoom 6
      • combine a/8/19/21.pbf and part of b/6/4/5.pbf (the tile needs to be unpacked, scaled, repacked)
• /vector/{mbtiles_name},{mbtiles_name}.json
  • solve name, maxzoom, bbox, center, ...

[klokan]

It seems to be done by Mapnik usually (see klokantech/tileserver-mapnik#13), but we may prefer an implementation without Mapnik dependency here.

[klokan]

The speed of the PBF JavaScript-native library https://github.com/mapbox/pbf has improved recently - if we decide to parse and reencode the PBFs for overzooming (scale + shift) at some point.

The https://github.com/mapbox/vector-tile-js is using it already.

In case we decide to go for mapnik C/C++ implementation, here is a node-js wrapper example:
https://github.com/naturalatlas/tilestrata-vtile-composite/blob/master/index.js
and the official documentation:
http://mapnik.org/documentation/node-mapnik/3.5/#VectorTile.composite

It would be practical to compare the speed of the two implementations, once finished.

[jingsam]

I would suggest not to implement this feature, as this feature is not only unnecessary but hard to properly implemented. One problem is how do you solve vector layer id conflict? What if I composite too much pbf s and exceed 500K limits?

Simple codes are easy to test and maintenance. Omit the unnecessary feature and keep the code clean, I suggest.