Functions that reveal whether a geometry is closed, empty, or simple

ST_IsClosed takes a linestring or multilinestring as an input parameter and returns 1 if the given linestring or multilinestring is closed. Otherwise, 0 (zero) is returned.

A linestring is closed if the start point and end point are equal. If the linestring has Z coordinates, the Z coordinates of the start point and end point must be equal. Otherwise, the points are not considered equal, and the linestring is not closed. A multilinestring is closed if each of its linestrings are closed.

ST_IsEmpty takes a geometry as an input parameter and returns 1 if the given geometry is empty. Otherwise 0 (zero) is returned.

A geometry is empty if it does not have any points that define it.

ST_IsSimple takes a geometry as an input parameter and returns 1 if the given geometry is simple. Otherwise, 0 (zero) is returned.

Points, polygons, and multipolygons are always simple. A linestring is simple if it does not pass through the same point twice. A multipoint is simple if it does not contain two equal points, and a multilinestring is simple if all of its linestrings are simple and the only intersections occur at points that are on the boundary of the linestrings in the multilinestring.