Name
ST_ExteriorRing — Returns the exteriorRing of a Polygon
Synopsis
geometry ST_ExteriorRing(bytea
Polygon);
Description
Returns the exteriorRing of a Polygon as LineString. It also works with Polygon or Multipolygon or GeometryCollection (containing Polygons). If the incoming geometry is a MULTIPOLYGON, it will return a MULTILINESTRING.
Coordinate Dimensions
| 2D | 3D | M |
|---|---|---|
 | | |
Spatial Standards Support
| OGC SFS for SQL. 1.1 (1999) | OGC SFS for SQL. 1.1.0 (2005) | OGC SFS for SQL. 1.2.0 (2006) | SQL-MM Part 3 |
|---|---|---|---|
| 2.1.10.1 | 7.2.15.1 | 7.2.13.1 | 8.2.3 |
Examples
--4D Polygon
SELECT ST_AsEWKT(ST_ExteriorRing(ST_GeomFromText('POLYGON ((20 20 10 10, 50 30 10 10, 20 50 -4 2, 20 20 4 2))')));
--Result
LINESTRING (20 20 10 10, 50 30 10 10, 20 50 -4 2, 20 20 4 2)
--Multipolygon
SELECT ST_AsEWKT(ST_ExteriorRing(ST_GeomFromText('MULTIPOLYGON (((0 0, 0 150, 150 150, 150 0, 0 0)),
((350 0, 230 0, 230 120, 350 120, 350 0)))')));
--Result
MULTILINESTRING ((0 0, 0 150, 150 150, 150 0, 0 0), (350 0, 230 0, 230 120, 350 120, 350 0))
--Polygon with a hole
SELECT ST_AsEWKT(ST_ExteriorRing(ST_GeomFromText('POLYGON ((20 20, 50 20, 50 50, 20 50, 20 20),
(30 40, 30 30, 40 30, 40 40, 30 40))')));
--Result
LINESTRING (20 20, 50 20, 50 50, 20 50, 20 20)
--LineString
SELECT ST_ExteriorRing(ST_GeomFromText('LINESTRING(10 50 50,10 20 55,10 0 50)'));
--Result
ERROR: es.upv.jaspa.exceptions.JASPAException: The geometry must be a Polygon, a MultiPolygon or a GeometryCollection
(made of some polygonal element/s): found LineString