Post Processing With Multiple Profiles?

[youngpm]

Hello! I was curious if it is possible to "post-process" multiple Profiles together before they are written to an MVT; in other words consider all the features in all layers that are going into the MVT. For example, if I had "buildings" and "roads" Profiles and wanted to tag a building with the closest road to it in the tile. Is such a thing possible?

I've seen the post-processing in the Profile interface but it wasn't obvious to me how to do any cross-Profile interaction.

Thanks!

[msbarry]

The API doesn't currently support this but it wouldn't be too hard to add. What do you think the right API for this would look like? something like (zoom, map<layer, list of features>) -> new map<layer, list of features>) ? or (zoom, list of features that include layer) -> new list of features that include layer or something different?

[msbarry]

I also wonder if there's a way to model dependencies between layers that are merged/created/dropped from other layers for classes in forwarding profile? Right now when you run with --only-layers=water,building it only loads the class for water and building but if they depended on transportation for post-processing then ideally we'd want it to automatically load transportation class too but omit the layer from the output.

[bdon]

Most of the Tilezen operations should work on the "visual" end-state output of the layer, after all merging/simplification, so expressing a dependency between layers would be better than doing redundant work by loading the features twice like I did above.

[msbarry]

I put out a prototype for this in #802. It adds a new method to Profile you can override to post-process features across layers.

  default Map<String, List<VectorTile.Feature>> postProcessTileFeatures(TileCoord tileCoord,
    Map<String, List<VectorTile.Feature>> layers) throws GeometryException {
    return layers; // default: do nothing
  }

Thoughts? If this looks good, we can hook it into ForwardingProfile to let complex profiles stack the transformation functions.

[youngpm]

Awesome, looks good to me!

[msbarry]

👍 just merged #802 so it should be possible now, will think some more about how to best handle splitting logic between classes in ForwardingProfile...