PolarDB:ST_Boundary

Syntax

geometry  ST_Boundary(geometry  geomA);

Parameters

Description

This function supports 3D objects and does not delete z coordinates.

Examples

• If you specify a point object, the function returns an empty GeometryCollection object.

  SELECT ST_AsText(ST_Boundary('POINT(1 0)'::geometry));
          st_astext
  --------------------------
   GEOMETRYCOLLECTION EMPTY
  (1 row)
                      

• If you specify a LineString object, the function returns a MultiPoint object.

  SELECT ST_AsText(ST_Boundary('LINESTRINGM(1 0 1, 2 0 2)'::geometry));
        st_astext
  ---------------------
   MULTIPOINT(1 0,2 0)
  (1 row)
                      

• If you specify a polygon object, the function returns a LineString object.

  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)
                      

• If you specify a polygon object containing holes, the function returns a MultiLineString object.

  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)