Generalize roads more at zoom levels 4 -- 6

layers/transportation/layer.sql

@@ -20,25 +20,25 @@ RETURNS TABLE(osm_id bigint, geometry geometry, class text, ramp int, oneway int
         brunnel(is_bridge, is_tunnel, is_ford) AS brunnel,
         NULLIF(service, '') AS service
     FROM (
-        -- etldoc: osm_highway_linestring_gen6 -> layer_transportation:z4
+        -- etldoc: osm_transportation_merge_linestring_gen6 -> layer_transportation:z4
         SELECT
             osm_id, geometry, highway, NULL AS railway, NULL AS service,
             NULL::boolean AS is_bridge, NULL::boolean AS is_tunnel,
             NULL::boolean AS is_ford,
             NULL::boolean AS is_ramp, NULL::boolean AS is_oneway,
             z_order
-        FROM osm_highway_linestring_gen6
+        FROM osm_transportation_merge_linestring_gen6
         WHERE zoom_level = 4
         UNION ALL
 
-        -- etldoc: osm_highway_linestring_gen5 -> layer_transportation:z5z6
+        -- etldoc: osm_transportation_merge_linestring_gen5 -> layer_transportation:z5z6
         SELECT
             osm_id, geometry, highway, NULL AS railway, NULL AS service,
             NULL::boolean AS is_bridge, NULL::boolean AS is_tunnel,
             NULL::boolean AS is_ford,
             NULL::boolean AS is_ramp, NULL::boolean AS is_oneway,
             z_order
-        FROM osm_highway_linestring_gen5
+        FROM osm_transportation_merge_linestring_gen5
         WHERE zoom_level BETWEEN 5 AND 6
         UNION ALL
 

layers/transportation/merge_highways.sql

@@ -0,0 +1,89 @@
+DROP MATERIALIZED VIEW IF EXISTS osm_transportation_merge_linestring CASCADE;
+DROP MATERIALIZED VIEW IF EXISTS osm_transportation_merge_linestring_gen5 CASCADE;
+DROP MATERIALIZED VIEW IF EXISTS osm_transportation_merge_linestring_gen6 CASCADE;
+
+
+DROP TRIGGER IF EXISTS trigger_flag2 ON osm_highway_linestring;
+DROP TRIGGER IF EXISTS trigger_refresh ON transportation.updates;
+
+-- 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_merge_linestring
+CREATE MATERIALIZED VIEW osm_transportation_merge_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[1] AS osm_id,
+        member_osm_ids,
+        highway,
+        z_order
+    FROM (
+      SELECT
+          ST_LineMerge(ST_Collect(geometry)) AS geometry,
+          highway,
+          min(z_order) AS z_order,
+          array_agg(DISTINCT osm_id) AS member_osm_ids
+      FROM osm_highway_linestring
+      WHERE highway IN ('motorway','trunk')
+      group by highway
+    ) AS highway_union
+);
+CREATE INDEX IF NOT EXISTS osm_transportation_merge_linestring_geometry_idx ON osm_transportation_merge_linestring USING gist(geometry);
+
+-- etldoc: osm_transportation_merge_linestring -> osm_transportation_merge_linestring_gen5
+CREATE MATERIALIZED VIEW osm_transportation_merge_linestring_gen5 AS (
+    SELECT ST_Simplify(geometry, 500) AS geometry, osm_id, member_osm_ids, highway, z_order
+    FROM osm_transportation_merge_linestring
+    WHERE highway IN ('motorway','trunk')  AND ST_Length(geometry) > 20000
+);
+CREATE INDEX IF NOT EXISTS osm_transportation_merge_linestring_gen5_geometry_idx ON osm_transportation_merge_linestring_gen5 USING gist(geometry);
+
+-- etldoc: osm_transportation_merge_linestring_gen5 -> osm_transportation_merge_linestring_gen6
+CREATE MATERIALIZED VIEW osm_transportation_merge_linestring_gen6 AS (
+    SELECT ST_Simplify(geometry, 2000) AS geometry, osm_id, member_osm_ids, highway, z_order
+    FROM osm_transportation_merge_linestring_gen5
+    WHERE highway IN ('motorway') AND ST_Length(geometry) > 20000
+);
+CREATE INDEX IF NOT EXISTS osm_transportation_merge_linestring_gen6_geometry_idx ON osm_transportation_merge_linestring_gen6 USING gist(geometry);
+
+
+-- Handle updates
+
+CREATE SCHEMA IF NOT EXISTS transportation;
+
+CREATE TABLE IF NOT EXISTS transportation.updates(id serial primary key, t text, unique (t));
+CREATE OR REPLACE FUNCTION transportation.flag() RETURNS trigger AS $$
+BEGIN
+    INSERT INTO transportation.updates(t) VALUES ('y')  ON CONFLICT(t) DO NOTHING;
+    RETURN null;
+END;
+$$ language plpgsql;
+
+CREATE OR REPLACE FUNCTION transportation.refresh() RETURNS trigger AS
+  $BODY$
+  BEGIN
+    RAISE LOG 'Refresh transportation';
+    REFRESH MATERIALIZED VIEW osm_transportation_merge_linestring;
+    REFRESH MATERIALIZED VIEW osm_transportation_merge_linestring_gen5;
+    REFRESH MATERIALIZED VIEW osm_transportation_merge_linestring_gen6;
+    DELETE FROM transportation.updates;
+    RETURN null;
+  END;
+  $BODY$
+language plpgsql;
+
+CREATE TRIGGER trigger_flag2
+    AFTER INSERT OR UPDATE OR DELETE ON osm_highway_linestring
+    FOR EACH STATEMENT
+    EXECUTE PROCEDURE transportation.flag();
+
+CREATE CONSTRAINT TRIGGER trigger_refresh
+    AFTER INSERT ON transportation.updates
+    INITIALLY DEFERRED
+    FOR EACH ROW
+    EXECUTE PROCEDURE transportation.refresh();

layers/transportation/transportation.yaml

@@ -64,6 +64,7 @@ layer:
     query: (SELECT geometry, class, oneway, ramp, brunnel, service FROM layer_transportation(!bbox!, z(!scale_denominator!))) AS t
 schema:
   - ./class.sql
+  - ./merge_highways.sql
   - ./layer.sql
 datasources:
   - type: imposm3