openmaptiles/layers/transportation_name/merge_highways.sql

-- Instead of using relations to find out the road names we
-- stitch together the touching ways with the same name
-- to allow for nice label rendering
-- Because this works well for roads that do not have relations as well

-- etldoc: osm_highway_linestring ->  osm_transportation_name_linestring
CREATE MATERIALIZED VIEW osm_transportation_name_linestring AS (
	SELECT
		(ST_Dump(geometry)).geom AS geometry,
        -- NOTE: The osm_id is no longer the original one which can make it difficult
        -- to lookup road names by OSM ID
		member_osm_ids[0] AS osm_id,
		member_osm_ids,
		name,
        ref,
		highway,
		z_order
	FROM (
		SELECT
			ST_LineMerge(ST_Union(geometry)) AS geometry,
			name,
            ref,
			highway,
			min(z_order) AS z_order,
			array_agg(DISTINCT osm_id) AS member_osm_ids
	    FROM osm_highway_linestring
        -- We only care about highways (not railways) for labeling
	    WHERE (name <> '' OR ref <> '') AND NULLIF(highway, '') IS NOT NULL
	    GROUP BY name, highway, ref
	) AS highway_union
);
CREATE INDEX IF NOT EXISTS osm_transportation_name_linestring_geometry_idx ON osm_transportation_name_linestring USING gist(geometry);

-- etldoc: osm_transportation_name_linestring -> osm_transportation_name_linestring_gen1
CREATE MATERIALIZED VIEW osm_transportation_name_linestring_gen1 AS (
    SELECT ST_Simplify(geometry, 50) AS geometry, osm_id, member_osm_ids, name, ref, highway, z_order
    FROM osm_transportation_name_linestring
    WHERE highway IN ('motorway','trunk')  AND ST_Length(geometry) > 8000
);
CREATE INDEX IF NOT EXISTS osm_transportation_name_linestring_gen1_geometry_idx ON osm_transportation_name_linestring_gen1 USING gist(geometry);

-- etldoc: osm_transportation_name_linestring_gen1 -> osm_transportation_name_linestring_gen2
CREATE MATERIALIZED VIEW osm_transportation_name_linestring_gen2 AS (
    SELECT ST_Simplify(geometry, 120) AS geometry, osm_id, member_osm_ids, name, ref, highway, z_order
    FROM osm_transportation_name_linestring_gen1
    WHERE highway IN ('motorway','trunk')  AND ST_Length(geometry) > 14000
);
CREATE INDEX IF NOT EXISTS osm_transportation_name_linestring_gen2_geometry_idx ON osm_transportation_name_linestring_gen2 USING gist(geometry);

-- etldoc: osm_transportation_name_linestring_gen2 -> osm_transportation_name_linestring_gen3
CREATE MATERIALIZED VIEW osm_transportation_name_linestring_gen3 AS (
    SELECT ST_Simplify(geometry, 120) AS geometry, osm_id, member_osm_ids, name, ref, highway, z_order
    FROM osm_transportation_name_linestring_gen2
    WHERE highway = 'motorway' AND ST_Length(geometry) > 20000
);
CREATE INDEX IF NOT EXISTS osm_transportation_name_linestring_gen3_geometry_idx ON osm_transportation_name_linestring_gen3 USING gist(geometry);

--- Triggers

CREATE OR REPLACE FUNCTION refresh_osm_transportation_name_linestring() RETURNS trigger AS
  $BODY$
  BEGIN
    REFRESH MATERIALIZED VIEW osm_transportation_name_linestring CONCURRENTLY;
    REFRESH MATERIALIZED VIEW osm_transportation_name_linestring_gen1 CONCURRENTLY;
    REFRESH MATERIALIZED VIEW osm_transportation_name_linestring_gen2 CONCURRENTLY;
    REFRESH MATERIALIZED VIEW osm_transportation_name_linestring_gen3 CONCURRENTLY;
      RETURN null;
  END;
  $BODY$
language plpgsql

CREATE TRIGGER trigger_refresh_osm_transportation_name_linestring
    AFTER INSERT OR UPDATE OR DELETE ON osm_highway_linestring
    FOR EACH STATEMENT
    EXECUTE PROCEDURE refresh_osm_transportation_name_linestring;