  An important issue in Qualitative Spatial Reasoning is the representation of
relative direction. In this paper we present simple geometric rules that enable
reasoning about relative direction between oriented points. This framework, the
Oriented Point Algebra OPRA_m, has a scalable granularity m. We develop a
simple algorithm for computing the OPRA_m composition tables and prove its
correctness. Using a composition table, algebraic closure for a set of OPRA
statements is sufficient to solve spatial navigation tasks. And it turns out
that scalable granularity is useful in these navigation tasks.
