Changes between Version 3 and Version 4 of UsersWikiSplitPolygonWithLineString

Timestamp:

04/06/15 17:27:32 (10 years ago)

Author:

Mike Taves

Comment:

handle holes better, and better example

UsersWikiSplitPolygonWithLineString

@@ -148 +148 @@
 Yo!Zik
 
-== Function: ST_SplitPolygon ==
-For versions of PostGIS before 2.0, a custom function can be used to split polygons using a linestring.
+== Function: `ST_SplitPolygon` ==
+A custom function can be used to split a `[Multi]Polygon` with a `[Multi]LineString` blade.
 {{{
-CREATE OR REPLACE FUNCTION ST_SplitPolygon(poly geometry, blade geometry)
-  RETURNS geometry AS
-'SELECT ST_Polygonize(ST_Union(ST_Boundary($1), $2))' LANGUAGE sql IMMUTABLE STRICT COST 100;
+CREATE OR REPLACE FUNCTION ST_SplitPolygon(poly geometry, blade geometry) RETURNS geometry AS
+'SELECT ST_Collect((d).geom)
+FROM (SELECT ST_Dump(ST_Polygonize(ST_Union(ST_Boundary($1), $2))) AS d) f
+WHERE ST_Area(ST_Intersection($1, (d).geom)) / ST_Area((d).geom) >= 1 - 1e-10;' LANGUAGE sql IMMUTABLE STRICT COST 100;
 }}}
 For example:
 {{{
-SELECT ST_AsText(ST_SplitPolygon(circle, line)) result
-FROM (SELECT 
-    ST_MakeLine(ST_MakePoint(10, 10),ST_MakePoint(190, 190)) line,
-    ST_Buffer(ST_GeomFromText('POINT(100 90)'), 50) circle) f;
+SELECT ST_AsText(ST_SplitPolygon(poly, blade)) AS result
+FROM (
+  SELECT 'POLYGON ((20 30, 100 180, 160 20, 20 30), (70 70, 92 105, 110 50, 70 70))'::geometry AS poly,
+    'MULTILINESTRING ((150 90, 90 70, 60 20), (50 140, 90 70))'::geometry AS blade
+) f;
 
            result
 -----------------------------------------
-GEOMETRYCOLLECTION(
-  POLYGON((150 90,...,150 90)),
-  POLYGON((60.1371179574584 60.1371179574584,...,60.1371179574584 60.1371179574584)))
+MULTIPOLYGON(((20 30,64.8275862068966 114.051724137931,80.4761904761905 86.6666666666667,
+  70 70,85.3846153846154 62.3076923076923,64.1095890410959 26.8493150684932,20 30)),
+((64.8275862068966 114.051724137931,100 180,135.555555555556 85.1851851851852,
+  102.131147540984 74.0437158469945,92 105,80.4761904761905 86.6666666666667,
+  64.8275862068966 114.051724137931)),
+((135.555555555556 85.1851851851852,160 20,64.1095890410959 26.8493150684932,
+  85.3846153846154 62.3076923076923,110 50,102.131147540984 74.0437158469945,
+  135.555555555556 85.1851851851852)))
 }}}