ST_Boundary

Syntax

geometry ST_Boundary(geometry geomA);

Parameters

Usage notes

• ST_Boundary supports 3D geometries and preserves Z coordinates in the output.

Examples

Point input — returns an empty GeometryCollection:

SELECT ST_AsText(ST_Boundary('POINT(1 0)'::geometry));

      st_astext
------------------------
 GEOMETRYCOLLECTION EMPTY
(1 row)

LineString input — returns a MultiPoint containing the endpoints:

SELECT ST_AsText(ST_Boundary('LINESTRINGM(1 0 1, 2 0 2)'::geometry));

    st_astext
---------------------
 MULTIPOINT(1 0,2 0)
(1 row)

Polygon input — returns a LineString representing the exterior ring:

SELECT ST_AsText(ST_Boundary('POLYGON((1 0, 2 0,0 2,1 0))'::geometry));

        st_astext
-----------------------------
 LINESTRING(1 0,2 0,0 2,1 0)
(1 row)

Polygon with holes — returns a MultiLineString containing the exterior and interior rings:

SELECT ST_AsText(ST_Boundary('POLYGON((1 0,3 0,0 3,1 0),(1 0 ,2 0, 0 2 ,1 0))'::geometry));

                      st_astext
------------------------------------------------------
 MULTILINESTRING((1 0,3 0,0 3,1 0),(1 0,2 0,0 2,1 0))
(1 row)

See also

• ST_AsText

• ST_ExteriorRing

• ST_MakePolygon