  A flat Universe model supported by recent observations has 18 possible
choices for its overall topology. To detect or exclude these possibilities is
one of the most important tasks in modern cosmology, but it has been very
difficult for globally inhomogeneous ones because of a long-time calculation.
In this brief paper we provide an object-based 3D method to overcome the
problem, as an extension of Fujii & Yoshii (2011a). Though the test depends on
the observer's location in the universe, this method drastically reduces
calculation times to constrain inhomogeneous topologies, and will be useful in
exhaustively constraining the size of the Universe.
