split_polygon

split_polygon.sql

CREATE OR REPLACE FUNCTION osm.split_polygon(polygon geometry, level integer)
  RETURNS SETOF geometry AS
$BODY$
DECLARE
  num_points int;
  mid double precision;
  envelope geometry;
  b1 geometry;
  b2 geometry;
  geom1 geometry;
  geom2 geometry;
BEGIN
  num_points = ST_NumPoints(ST_ExteriorRing(polygon));
  IF num_points < 1000 THEN
    RETURN NEXT polygon;
    RETURN;
  END IF;
  envelope = ST_Envelope(polygon);
  IF ST_XMax(envelope) - ST_XMin(envelope) < ST_YMax(envelope) - ST_YMin(envelope) THEN
    mid = (ST_YMax(envelope) + ST_YMin(envelope)) / 2;
    b1 = ST_MakeEnvelope(ST_XMin(envelope), ST_YMin(envelope), ST_XMax(envelope), mid);
    b2 = ST_MakeEnvelope(ST_XMin(envelope), mid, ST_XMax(envelope), ST_YMax(envelope));
  ELSE
    mid = (ST_XMax(envelope) + ST_XMin(envelope)) / 2;
    b1 = ST_MakeEnvelope(ST_XMin(envelope), ST_YMin(envelope), mid, ST_YMax(envelope));
    b2 = ST_MakeEnvelope(mid, ST_YMin(envelope), ST_XMax(envelope), ST_YMax(envelope));
  END IF;
 
  geom1 = ST_ClipByBox2D(polygon, b1);
  geom2 = ST_ClipByBox2D(polygon, b2);
 
  IF (GeometryType(geom1) = 'POLYGON' OR GeometryType(geom1) = 'MULTIPOLYGON') AND
     (GeometryType(geom2) = 'POLYGON') OR (GeometryType(geom2) = 'MULTIPOLYGON') THEN
    FOR i IN 1..ST_NumGeometries(geom1) LOOP
      RETURN QUERY SELECT osm.split_polygon(ST_GeometryN(geom1,i), level+1);
    END LOOP;
    FOR i IN 1..ST_NumGeometries(geom2) LOOP
      RETURN QUERY SELECT osm.split_polygon(ST_GeometryN(geom2,i), level+1);
    END LOOP;
    RETURN;
  END IF;
  
  RETURN NEXT polygon;
END;
$BODY$

The above PL/pgSQL is ported from osmcoastline C++. No support for expand to overlap and destination should be a parameter but perhaps this might be useful for some since it works directly in postgis. Also some hardcoded SRS 3006 here and there...

Replacing ST_Intersects with ST_ClipByBox2D still give good output for me :) Was 5x faster than ST_Subdivide before this and now it's something like 50x faster. :)

Refactored to return SETOF geometry and removed hardcoded SRS.