The ST_WithinFilter method provides an efficient test to determine if one geometry might be within the other.
Returns 1 if the geometry-expression might be within geo2, otherwise 0.
This test is cheaper than ST_Within, but may return 1 in some cases where
the geometry-expression is not actually spatially within geo2.
Therefore, this method can be useful as a primary filter when further processing will determine if geometries
interact in the desired way.
The implementation of ST_WithinFilter relies upon meta-data associated with the stored geometries.
Because the available meta-data may change between server versions, depending upon how the data is loaded, or
where ST_WithinFilter is used within a query,
the expression geometry-expression.ST_WithinFilter(geo2)
can return different results when geometry-expression is not within
Whenever geometry-expression is within geo2,
ST_WithinFilter will always return 1.
This method can not be used with geometries in round-Earth spatial reference system.