Build aggregation on zoom level 13 (#936)

* Building aggregation at zoom 13

layers/building/building.sql

@@ -82,7 +82,7 @@ SELECT geometry,
        CASE WHEN hide_3d THEN TRUE END AS hide_3d
 FROM (
          SELECT
-             -- etldoc: osm_building_polygon_gen1 -> layer_building:z13
+             -- etldoc: osm_building_block_gen1 -> layer_building:z13
              osm_id,
              geometry,
              NULL::int  AS render_height,
@@ -90,7 +90,7 @@ FROM (
              NULL::text AS material,
              NULL::text AS colour,
              FALSE      AS hide_3d
-         FROM osm_building_polygon_gen1
+         FROM osm_building_block_gen1
          WHERE zoom_level = 13
            AND geometry && bbox
          UNION ALL

layers/building/building.yaml

@@ -20,6 +20,7 @@ layer:
     hide_3d: |
         If True, building (part) should not be rendered in 3D. Currently, [building outlines](https://wiki.openstreetmap.org/wiki/Simple_3D_buildings) are marked as hide_3d.
 schema:
+  - ./update_building.sql
   - ./building.sql
 datasources:
   - type: imposm3

layers/building/mapping.yaml

@@ -1,9 +1,9 @@
-generalized_tables:
+#generalized_tables:
-  # etldoc: imposm3 -> osm_building_polygon_gen1
+#  # etldoc: imposm3 -> osm_building_polygon_gen1
-  building_polygon_gen1:
+#  building_polygon_gen1:
-    source: building_polygon
+#    source: building_polygon
-    sql_filter: area>power(ZRES12,2) AND ST_IsValid(geometry)
+#    sql_filter: area>power(ZRES12,2) AND ST_IsValid(geometry)
-    tolerance: ZRES14
+#    tolerance: ZRES14
 
 tables:
   # etldoc: imposm3 -> osm_building_polygon

layers/building/update_building.sql

@@ -0,0 +1,125 @@
+DROP TRIGGER IF EXISTS trigger_refresh ON buildings.updates;
+DROP TRIGGER IF EXISTS trigger_flag ON osm_building_polygon;
+
+--creating aggregated building blocks with removed small polygons and small
+--holes. Aggregated polygons are simplified.
+
+--function returning recordset for matview
+--returning recordset of buildings aggregates by zres 14, with removed small
+--holes and with removed small buildings/blocks
+--
+
+CREATE OR REPLACE FUNCTION osm_building_block_gen1()
+    RETURNS table
+            (
+                osm_id   bigint,
+                geometry geometry
+            )
+AS
+$$
+DECLARE
+    zres14 float := Zres(14);
+    zres12 float := Zres(12);
+BEGIN
+    FOR osm_id, geometry IN
+        WITH dta AS ( -- CTE is used because of optimization
+            SELECT o.osm_id, o.geometry, ST_ClusterDBSCAN(o.geometry, eps := zres14, minpoints := 1) OVER () cid
+            FROM osm_building_polygon o
+        )
+        SELECT (array_agg(dta.osm_id))[1]                                                                   osm_id,
+               ST_Buffer(ST_MemUnion(ST_Buffer(dta.geometry, zres14, 'join=mitre')), -zres14, 'join=mitre') geometry
+        FROM dta
+        GROUP BY cid
+
+        LOOP
+            -- removing holes smaller than
+            IF ST_NumInteriorRings(geometry) > 0 THEN -- only from geometries wih holes
+                geometry := (
+                    -- there are some multi-geometries in this layer
+                    SELECT ST_Collect(gn)
+                    FROM (
+                             -- in some cases are "holes" NULL, because all holes are smaller than
+                             SELECT COALESCE(
+                                        -- exterior ring
+                                            ST_MakePolygon(ST_ExteriorRing(dmp.geom), holes),
+                                            ST_MakePolygon(ST_ExteriorRing(dmp.geom))
+                                        ) gn
+
+                             FROM ST_Dump(geometry) dmp, -- 1 dump polygons
+                                  LATERAL (
+                                      SELECT array_agg(ST_Boundary(rg.geom)) holes -- 2 create array
+                                      FROM ST_DumpRings(dmp.geom) rg -- 3 from rings
+                                      WHERE rg.path[1] > 0 -- 5 except inner ring
+                                        AND ST_Area(rg.geom) >= power(zres12, 2) -- 4 bigger than
+                                      ) holes
+                         ) new_geom
+                );
+            END IF;
+
+            IF ST_Area(geometry) < power(zres12, 2) THEN
+                CONTINUE;
+            END IF;
+
+            -- simplify
+            geometry := ST_SimplifyPreserveTopology(geometry, zres14::float);
+
+            RETURN NEXT;
+        END LOOP;
+END;
+$$ LANGUAGE plpgsql STABLE
+                    STRICT
+                    PARALLEL SAFE;
+
+
+DROP MATERIALIZED VIEW IF EXISTS osm_building_block_gen1;
+
+CREATE MATERIALIZED VIEW osm_building_block_gen1 AS
+SELECT *
+FROM osm_building_block_gen1();
+
+CREATE INDEX ON osm_building_block_gen1 USING gist (geometry);
+CREATE UNIQUE INDEX ON osm_building_block_gen1 USING btree (osm_id);
+
+
+-- Handle updates
+
+CREATE SCHEMA IF NOT EXISTS buildings;
+
+CREATE TABLE IF NOT EXISTS buildings.updates
+(
+    id serial PRIMARY KEY,
+    t  text,
+    UNIQUE (t)
+);
+
+CREATE OR REPLACE FUNCTION buildings.flag() RETURNS trigger AS
+$$
+BEGIN
+    INSERT INTO buildings.updates(t) VALUES ('y') ON CONFLICT(t) DO NOTHING;
+    RETURN NULL;
+END;
+$$ LANGUAGE plpgsql;
+
+CREATE OR REPLACE FUNCTION buildings.refresh() RETURNS trigger AS
+$$
+BEGIN
+    RAISE LOG 'Refresh buildings block';
+    REFRESH MATERIALIZED VIEW osm_building_block_gen1;
+    -- noinspection SqlWithoutWhere
+    DELETE FROM buildings.updates;
+    RETURN NULL;
+END;
+$$ LANGUAGE plpgsql;
+
+CREATE TRIGGER trigger_flag
+    AFTER INSERT OR UPDATE OR DELETE
+    ON osm_building_polygon
+    FOR EACH STATEMENT
+EXECUTE PROCEDURE buildings.flag();
+
+CREATE CONSTRAINT TRIGGER trigger_refresh
+    AFTER INSERT
+    ON buildings.updates
+    INITIALLY DEFERRED
+    FOR EACH ROW
+EXECUTE PROCEDURE buildings.refresh();