could not register providers: error fetching geometry type for layer (polygon): layer (polygon) returned unsupported geometry type (<nil>)

[valodo]

Hello,

I'm trying to create two layers (polygon and line) using mvt_postgis as provider type, but Tegola shows the following error:

Error: could not register providers: error fetching geometry type for layer (polygon): layer (polygon) returned unsupported geometry type (<nil>) if custom parameters are used, remember to set geometry_type for the provider could not register providers: error fetching geometry type for layer (polygon): layer (polygon) returned unsupported geometry type (<nil>) if custom parameters are used, remember to set geometry_type for the provider

I run Tegola using TEGOLA_SQL_DEBUG=LAYER_SQL:EXECUTE_SQL environment variable and --log-level TRACE in order to understand the problem. However, there was not any detailed information and it stops.

Tegola is configured as follow:

...

[[providers]]
name = "geometries"
type = "mvt_postgis"
uri = "postgres://admin:admin@pgsql-1:5432/geometries" 
srid = 3857 

    [[providers.layers]]
    name = "polygon" 
    sql = "SELECT id, ST_AsMVTGeom(web_mercator_geometry, !BBOX!) AS geom FROM public.polygon WHERE web_mercator_geometry && !BBOX!"

    [[providers.layers]]
    name = "line" 
    sql = "SELECT id, ST_AsMVTGeom(web_mercator_geometry, !BBOX!) AS geom FROM public.line WHERE web_mercator_geometry && !BBOX!"

...

The polygon table contains the following geometry with SRID 3857: POLYGON((1413593.3073259895 5144415.67802485,1413593.3073259895 5144416.077882397,1413593.5072557947 5144416.077882397,1413593.5072557947 5144415.67802485,1413593.3073259895 5144415.67802485))

Instead, the line table contains the following geometry with SRID 3857: LINESTRING(1408373.086449311 5130567.4123749705,1408371.0812513235 5130565.82138195,1408370.770669944 5130565.292494416,1408370.3621274128 5130564.5972656775)

Is there a way to understand what is the problem and how the geometries are null?

[ARolek]

@valodo this is a long standing wart in tegola, but essentially tegola is trying to infer your geometry type by forming up some SQL and then making a roundtrip to the database. This works when the SQL is simple, but can break in other situations. The work around is to set the geometry_type attribute on the provider.layer config:

[[providers]]
name = "geometries"
type = "mvt_postgis"
uri = "postgres://admin:admin@pgsql-1:5432/geometries" 
srid = 3857 

    [[providers.layers]]
    name = "polygon" 
    geometry_type = "polygon"
    sql = "SELECT id, ST_AsMVTGeom(web_mercator_geometry, !BBOX!) AS geom FROM public.polygon WHERE web_mercator_geometry && !BBOX!"

    [[providers.layers]]
    name = "line" 
    geometry_type = "linestring"
    sql = "SELECT id, ST_AsMVTGeom(web_mercator_geometry, !BBOX!) AS geom FROM public.line WHERE web_mercator_geometry && !BBOX!"

This is documented here and here

[valodo]

Thank you for your answer. The configuration with geometry_type solves the problem.

[ARolek]

Great!