STIsRing (geometry Data Type)
Returns 1 if a geometry instance fulfills the following requirements:
It is a LineString instance.
It is closed.
It is simple.
Returns 0 if the LineString instance does not meet the requirements.
For a geometry instance to be closed and simple, both STIsClosed() and STIsSimple() must return 1 when invoked on the instance. To determine the instance type of a geometry, use STGeometryType().