Name
ST_Boundary — Returns the closure of the combinatorial boundary of a Geometry
Synopsis
geometry (bytea
Geometry);
Description
Returns the closure of the combinatorial boundary of this Geometry. The elements of a boundary shall be smaller in dimension than the original element, exactly the next lower dimension.
The boundary of a node is the empty set.
The boundary of a line is the empty set if it's closed, otherwise it's the set containing the start and end points.
The boundary of a surface is the set of lines that delineate the edge of the surface, including interior and exterior rings.
![[Caution]](images/caution.png) | |
If the input geometry is a GEOMETRYCOLLECTION, it throws an error |
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 |
|---|---|---|---|
| 2.1.1.1 | 7.2.10.1 | 7.2.8.1 | 5.1.14 |
Examples
--Polygon
SELECT ST_AsText(ST_Boundary(ST_GeomFromText('POLYGON ((20 20, 50 20, 50 50, 20 50, 20 20))')));
--Result
LINESTRING (20 20, 50 20, 50 50, 20 50, 20 20)
--LineString
SELECT ST_AsText(ST_Boundary(ST_GeomFromText('MULTILINESTRING((10 48,10 21,10 0),(16 0,16 23,16 48))')));
--Result
MULTIPOINT (10 0, 10 48, 16 0, 16 48)
--4D LineString
SELECT ST_AsText(ST_Boundary(ST_GeomFromText('LINESTRING(0 0 2 -4,5 0 8 -4,10 0 6 -2)')));
--Result
MULTIPOINT (0 0 2 -4, 10 0 6 -2)
--Multipoint
SELECT ST_AsText(ST_Boundary(ST_GeomFromText('MULTIPOINT (0 0, 1 1, 2 2)')));
--Result
null