Changes between Version 4 and Version 5 of UsersWikiBuildPolygonsWithLines

Timestamp:

Apr 9, 2015, 10:29:55 PM (9 years ago)

Author:

Mike Taves

Comment:

also ST_PolygonizeLinework

UsersWikiBuildPolygonsWithLines

@@ -6 +6 @@
 #!sql
 CREATE OR REPLACE FUNCTION ST_BuildAreaLinework(linework geometry) RETURNS geometry AS
-'WITH data AS (SELECT * FROM ST_Dump(ST_UnaryUnion($1)))
+$BODY$WITH data AS (SELECT * FROM ST_Dump(ST_UnaryUnion($1)))
 SELECT ST_SetSRID(ST_BuildArea(ST_Collect(geom)), ST_SRID($1))
 FROM
-(
+( -- This is the noded linework, broken up where they cross each other
   SELECT (ST_Dump(ST_Union(geom))).geom FROM data
 ) t1,
-(
+( -- This is a [MULTI]POINT of any crossings or closures
   SELECT ST_Union(geom) AS pt
   FROM (
@@ -21 +21 @@
   ) s
 ) t2
-WHERE ST_Intersects(ST_StartPoint(geom), pt) AND ST_Intersects(ST_EndPoint(geom), pt);' LANGUAGE sql IMMUTABLE;
+WHERE ST_Intersects(ST_StartPoint(geom), pt) AND ST_Intersects(ST_EndPoint(geom), pt);$BODY$ LANGUAGE sql IMMUTABLE;
 }}}
 
@@ -30 +30 @@
 }}}
 
-Where the yellow lines are the input linework, and the yellow polygon with a hole is the result.
+Where the blue lines are the input linework, and the yellow polygon with a hole is the result.
 
 [[Image(BuildAreaLinework_example.png)]]
+
+----
+
+A similar function could be used with ST_Polygonize
+{{{
+#!sql
+CREATE OR REPLACE FUNCTION ST_PolygonizeLinework(linework geometry) RETURNS geometry AS
+$BODY$WITH data AS (SELECT * FROM ST_Dump(ST_UnaryUnion($1)))
+SELECT ST_SetSRID(ST_Polygonize(geom), ST_SRID($1))
+FROM
+( -- This is the noded linework, broken up where they cross each other
+  SELECT (ST_Dump(ST_Union(geom))).geom FROM data
+) t1,
+( -- This is a [MULTI]POINT of any crossings or closures
+  SELECT ST_Union(geom) AS pt
+  FROM (
+    SELECT ST_Intersection(A.geom, B.geom) AS geom
+    FROM data A, data B
+    WHERE A.path[1] < B.path[1] AND ST_Intersects(A.geom, B.geom)
+    UNION SELECT ST_StartPoint(geom) FROM data WHERE ST_IsClosed(geom)
+  ) s
+) t2
+WHERE ST_Intersects(ST_StartPoint(geom), pt) AND ST_Intersects(ST_EndPoint(geom), pt);$BODY$ LANGUAGE sql IMMUTABLE;
+}}}
+
+For example:
+{{{
+#!sql
+SELECT ST_PolygonizeLinework('MULTILINESTRING((50 40,50 230,300 230,270 60,40 60),(150 30,130 240),(191 155,240 190,250 150,190 170))');
+}}}
+
+Where the blue lines are the input linework, and the yellow polygons (`GEOMETRYCOLLECTION(POLYGON((...)))`) are the result.
+
+[[Image(PolygonizeLinework_example.png)]]
 
 == External links ==