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ST_ExteriorRing Prev 8.5. Geometry Accessors Next ST_ExteriorRing — Returns a line string representing the exterior ring of the POLYGON geometry. Return NULL if the geometry is not a polygon. Will not work with MULTIPOLYGON geometry ST_ExteriorRing ( geometry a_polygon ) ; Returns a line string representing the exterior ring of the POLYGON geometry. Return NULL if the geometry is not a polygon. Only works with POLYGON geometry types This method implements the OpenGIS Simple Features Implementation Specification for SQL 1.1. 2.1.5.1 This method implements the SQL/MM specification. SQL-MM 3: 8.2.3, 8.3.3 This function supports 3d and will not drop the z-index. --If you have a table of polygons SELECT gid, ST_ExteriorRing(the_geom) AS ering FROM sometable; --If you have a table of MULTIPOLYGONs --and want to return a MULTILINESTRING composed of the exterior rings of each polyg...

ST_Boundary Prev 8.5. Geometry Accessors Next ST_Boundary — Returns the closure of the combinatorial boundary of this Geometry. geometry ST_Boundary ( geometry geomA ) ; 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 Prior to 2.0.0, this function throws an exception if used with GEOMETRYCOLLECTION . From 2.0.0 up it will return NULL instead (unsupported input). This method implements the OpenGIS Simple Features Implementation Specification for SQL 1.1. OGC SPEC s2.1.1.1 This method implements the SQL/MM specification. ...

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