Shekhar, ShashiLiu, XuanChawla, Sanjay2020-09-022020-09-021999-07-21https://hdl.handle.net/11299/215382Direction is an important spatial relationship that is used in many fields such as geographic information systems (GIS) and image interpretation. It is also frequently used as a selection condition in spatial queries. In our recent work we have described a novel viewpoint to model direction as a `spatial object' based upon the concepts of vectors, points and angles. This was a departure from the conventional approach of treating direction as a spatial relationship between objects. In this paper, based upon `direction objects', we partition the directional space into a set of equivalence classes. By defining an algebra on equivalence classes we provide a framework to model semantics of direction predicates for qualitative spatial reasoning. We then proceed to extrapolate the definition of direction equivalence classes to define `path' equivalence classes with an application to the landmark-based route description problem. Keywords: Directional relationships, Direction objects, Equivalence Classes, Landmark-based routing.en-USReport