Reasoning with Topological and Directional Spatial Information
  Current research on qualitative spatial representation and reasoning mainly
focuses on one single aspect of space. In real world applications, however,
multiple spatial aspects are often involved simultaneously.
  This paper investigates problems arising in reasoning with combined
topological and directional information. We use the RCC8 algebra and the
Rectangle Algebra (RA) for expressing topological and directional information
respectively. We give examples to show that the bipath-consistency algorithm
BIPATH is incomplete for solving even basic RCC8 and RA constraints. If
topological constraints are taken from some maximal tractable subclasses of
RCC8, and directional constraints are taken from a subalgebra, termed DIR49, of
RA, then we show that BIPATH is able to separate topological constraints from
directional ones. This means, given a set of hybrid topological and directional
constraints from the above subclasses of RCC8 and RA, we can transfer the joint
satisfaction problem in polynomial time to two independent satisfaction
problems in RCC8 and RA. For general RA constraints, we give a method to
compute solutions that satisfy all topological constraints and approximately
satisfy each RA constraint to any prescribed precision.
