gistfile1.sql

CREATE OR REPLACE FUNCTION gis.split_polygon(poly geometry, expand double precision DEFAULT 0.0001, srid integer DEFAULT 3857, level integer DEFAULT 0)
  RETURNS SETOF geometry AS
$BODY$
declare
num_points integer;
env geometry;
p1 geometry;
p2 geometry;
b1 geometry;
b2 geometry;
mid double precision;
diffx double precision;
diffy double precision;
tmp geometry;
begin
if geometrytype(poly) != 'POLYGON' then
	raise notice 'not a polygon! %', st_geometrytype(poly);
	return;
end if;

num_points := ST_NumPoints(ST_ExteriorRing(poly));
if num_points < 500 or level > 1000 then
	return next poly;
	return;
	--raise notice 'end %', level;
else
	env := ST_Envelope(poly);
	diffx := st_xmax(env) - st_xmin(env);
	diffy := st_ymax(env) - st_ymin(env); 
	
	if diffx < st_ymax(env) - st_ymin(env) then
		if expand * 4 >= diffy then
			return next poly;
			return;
		end if;
		mid := diffy / 2.0;
		b1 := ST_MakeEnvelope(st_xmin(env), st_ymin(env), st_xmax(env), st_ymin(env)+mid,       srid);
		b2 := ST_MakeEnvelope(st_xmin(env), st_ymin(env)+mid,       st_xmax(env), st_ymax(env), srid);
	else
		if expand * 4 >= diffx then
			return next poly;
			return;
		end if;
		mid := diffx / 2.0;
		b1 := ST_MakeEnvelope(st_xmin(env), st_ymin(env), st_xmin(env)+mid,       st_ymax(env), srid);
		b2 := ST_MakeEnvelope(st_xmin(env)+mid,       st_ymin(env), st_xmax(env), st_ymax(env), srid);
	end if;

	b1 := ST_SnapToGrid(ST_Expand(b1, expand), expand/2);
	b2 := ST_SnapToGrid(ST_Expand(b2, expand), expand/2);

	--raise notice 'split %d', level;
 	begin
		p1 := ST_Intersection(poly, b1);
		p2 := ST_Intersection(poly, b2);
	exception when others then begin
		raise notice 'buffer poly' ;
		tmp := st_buffer(poly,0);
		p1 := ST_Intersection(tmp, b1);
		p2 := ST_Intersection(tmp, b2);
	exception when others then
		return next poly;
		return;
	end; end;

	return query select gis.split_polygon(p.geom, expand, srid, level + 1) from 
		(select (ST_Dump(p1)).geom as geom) p where st_dimension(p.geom) = 2;
	return query select gis.split_polygon(p.geom, expand, srid, level + 1) from 
		(select (ST_Dump(p2)).geom as geom) p where st_dimension(p.geom) = 2;

end if;
end;
$BODY$
  LANGUAGE plpgsql IMMUTABLE;