Support for multi-layer tiles

[robert-claypool]

I would like your thoughts on how to generate multi-layer tiles.

My idea is to allow requests like /{schema_name}.{table_name},{schema_name}.{table_name}/{z}/{x}/{y}.pbf and use binary concatenation of ST_AsMVT statements to produce the tile, see https://postgis.net/docs/ST_AsMVT.html

I believe the only way to do this now is via function source, for example:

CREATE OR REPLACE FUNCTION
  public.assets(z integer, x integer, y integer, query_params json)
RETURNS bytea
AS
$$
-- Prefer z,x,y inputs over z,x,y table columns.
#variable_conflict use_variable
DECLARE
  poles_mvt bytea;
  meters_mvt bytea;
BEGIN
  SELECT INTO poles_mvt
    ST_AsMVT(tile, 'public.poles', 4096, 'geom')
    FROM (
      SELECT
        ST_AsMVTGeom(shape, TileBBox(z, x, y, 3857), 4096, 64, true) AS geom
        ,"pole_number"
      FROM public.switches
      WHERE shape && TileBBox(z, x, y, 3857)
    ) AS tile
    WHERE geom IS NOT NULL;

  SELECT INTO meters_mvt
    ST_AsMVT(tile, 'public.meters', 4096, 'geom')
    FROM (
      SELECT
        ST_AsMVTGeom(shape, TileBBox(z, x, y, 3857), 4096, 64, true) AS geom
        ,"meter_number"
      FROM public.meters
      WHERE shape && TileBBox(z, x, y, 3857)
    ) AS tile
    WHERE geom IS NOT NULL;

  RETURN poles_mvt || meters_mvt;
END
$$
LANGUAGE plpgsql IMMUTABLE STRICT PARALLEL SAFE;

I have never developed in Rust, but Martin's codebase is so clean I could probably make these changes and issue a decent PR. What do you think?

[stepankuzmin]

Thanks for posting this, @robert-claypool!

It's planned to support multi-layered table sources and that's exactly the way I imagined that! I would gladly review PR for this.

[robert-claypool]

Priorities at work have changed, and so it looks like I won't be working on this for the foreseeable future.

[stepankuzmin]

No problem, I'll keep this issue open and implement this in future releases.

[robert-claypool]

I need this feature for an August deadline. @fielda will sponsor the work and open source it, please contact me if interested (email address is in my GitHub profile).

[stepankuzmin]

Hi @robert-claypool! Thanks for your patience. I've made experimental support for composite sources in #107

You can now compose table sources by listing the tables separated by a comma:

http://0.0.0.0:3000/public.red_points,public.blue_points.json
http://0.0.0.0:3000/public.red_points,public.blue_points/0/0/0.pbf

Could you please try this docker image with composite sources support and give any feedback on this?

docker pull urbica/martin:pr-107-merge

[sabman]

Just tried it locally with two rather large layers (lines+polygons) works really well!! 🥳

Will do some more testing tomorrow.

[dechristopher]

This looks like it can be closed now. Thanks for the work, everyone.