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ST_BOUNDARY

Returns the combinatorial boundary of a geometry. For a Polygon, this is the line string defining the boundary.

Syntax

ST_BOUNDARY(g)
BOUNDARY(g)

Description

Returns a geometry that is the closure of the combinatorial boundary of the geometry value g.

BOUNDARY() is a synonym.

Examples

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SELECT ST_AsText(ST_Boundary(ST_GeomFromText('LINESTRING(3 3,0 0, -3 3)')));
+----------------------------------------------------------------------+
| ST_AsText(ST_Boundary(ST_GeomFromText('LINESTRING(3 3,0 0, -3 3)'))) |
+----------------------------------------------------------------------+
| MULTIPOINT(3 3,-3 3)                                                 |
+----------------------------------------------------------------------+

SELECT ST_AsText(ST_Boundary(ST_GeomFromText('POLYGON((3 3,0 0, -3 3, 3 3))')));
+--------------------------------------------------------------------------+
| ST_AsText(ST_Boundary(ST_GeomFromText('POLYGON((3 3,0 0, -3 3, 3 3))'))) |
+--------------------------------------------------------------------------+
| LINESTRING(3 3,0 0,-3 3,3 3)                                             |
+--------------------------------------------------------------------------+