Name
ST_Boundary — Returns the boundary of a geometry.
Synopsis
geometry ST_Boundary(geometry geomA);
Description
Returns the closure of the combinatorial boundary of this Geometry. The combinatorial boundary is defined as described in section 3.12.3.2 of the OGC SPEC. Because the result of this function is a closure, and hence topologically closed, the resulting boundary can be represented using representational geometry primitives as discussed in the OGC SPEC, section 3.12.2.
Performed by the GEOS module
![[Note]](../images/note.png)
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Prior to 2.0.0, this function throws an exception if used with |
This method implements the OGC Simple Features
Implementation Specification for SQL 1.1.
OGC SPEC s2.1.1.1
This method implements the SQL/MM specification.
SQL-MM IEC 13249-3: 5.1.17
This function supports 3d and will not drop the z-index.
Enhanced: 2.1.0 support for Triangle was introduced
Changed: 3.2.0 support for TIN, does not use geos, does not linearize curves
Examples
LineString with boundary points overlaid.
SELECT ST_Boundary(geom)
FROM (SELECT 'LINESTRING(100 150,50 60,70 80,160 170)'::geometry As geom) As f;
MULTIPOINT((100 150),(160 170))
Polygon holes with the boundary MultiLineString overlaid.
SELECT ST_Boundary(geom)
FROM (SELECT
'POLYGON (( 10 130,50 190,110 190,140 150,150 80,100 10,20 40,10 130 ),
( 70 40,100 50,120 80,80 110,50 90,70 40 ))'::geometry As geom) As f;
MULTILINESTRING((10 130,50 190,110 190,140 150,150 80,100 10,20 40,10 130),
(70 40,100 50,120 80,80 110,50 90,70 40))
SELECT ST_Boundary('LINESTRING(1 1,0 0,-1 1)');
MULTIPOINT((1 1),(-1 1))
SELECT ST_Boundary('POLYGON((1 1,0 0,-1 1,1 1))');
LINESTRING(1 1,0 0,-1 1,1 1)
This example uses a 3D polygon.
SELECT ST_Boundary('POLYGON((1 1 1,0 0 1,-1 1 1,1 1 1))');
LINESTRING(1 1 1,0 0 1,-1 1 1,1 1 1)
This example uses a 3D MultiLineString.
SELECT ST_Boundary('MULTILINESTRING((1 1 1,0 0 0.5,-1 1 1),(1 1 0.5,0 0 0.5,-1 1 0.5,1 1 0.5) )');
MULTIPOINT(1 1 1,-1 1 1)