Removes any small rings from a geometry.
One or more of the following criteria may be used to determine if a ring is to be considered small:
the length of the diagonal of the ring's MBR
the area of the ring
the ratio of the ring's area to the square of its perimeter. This is always less than pi/4 and is actually independent of the size of the ring but will be small if its shape is irregular.
If any of these parameters is negative it is ignored.
Parameter 1 - any geometry.
Parameter 2 - the maximum MBR diagonal length.
Parameter 3 (Optional) - the maximum ring area.
Parameter 4 (Optional) - the maximum area to square perimeter ratio.
Returns: the resulting geometry with small rings removed, or null if all of the rings are too small.
Note: This function does not fully support 3D geometries. Any 3D geometries will be projected down to 2 dimensions.