Major breakthrough, just some artifacting to resolve

layers/housenumber/housenumber_centroid.sql

@@ -1,4 +1,45 @@
+DROP TRIGGER IF EXISTS trigger_flag ON osm_housenumber_point;
+DROP TRIGGER IF EXISTS trigger_refresh ON housenumber.updates;
 
 -- etldoc: osm_housenumber_point -> osm_housenumber_point
-UPDATE osm_housenumber_point SET geometry=topoint(geometry)
-WHERE ST_GeometryType(geometry) <> 'ST_Point';
+CREATE OR REPLACE FUNCTION convert_housenumber_point() RETURNS VOID AS $$
+BEGIN
+  UPDATE osm_housenumber_point SET geometry=ST_PointOnSurface(geometry) WHERE ST_GeometryType(geometry) <> 'ST_Point';
+END;
+$$ LANGUAGE plpgsql;
+
+SELECT convert_housenumber_point();
+
+-- Handle updates
+
+CREATE SCHEMA IF NOT EXISTS housenumber;
+
+CREATE TABLE IF NOT EXISTS housenumber.updates(id serial primary key, t text, unique (t));
+CREATE OR REPLACE FUNCTION housenumber.flag() RETURNS trigger AS $$
+BEGIN
+    INSERT INTO housenumber.updates(t) VALUES ('y')  ON CONFLICT(t) DO NOTHING;
+    RETURN null;
+END;    
+$$ language plpgsql;
+
+CREATE OR REPLACE FUNCTION housenumber.refresh() RETURNS trigger AS
+  $BODY$
+  BEGIN
+    RAISE LOG 'Refresh housenumber';
+    PERFORM convert_housenumber_point();
+    DELETE FROM housenumber.updates;
+    RETURN null;
+  END;
+  $BODY$
+language plpgsql;
+
+CREATE TRIGGER trigger_flag
+    AFTER INSERT OR UPDATE OR DELETE ON osm_housenumber_point
+    FOR EACH STATEMENT
+    EXECUTE PROCEDURE housenumber.flag();
+
+CREATE CONSTRAINT TRIGGER trigger_refresh
+    AFTER INSERT ON housenumber.updates
+    INITIALLY DEFERRED
+    FOR EACH ROW
+    EXECUTE PROCEDURE housenumber.refresh();