A qualitative trajectory calculus as a basis for representing moving objects in Geographical Information Systems

Qualitative formalisms, suited to express qualitative temporal or spatial relationships between entities, have gained wide acceptance as a useful way of abstracting from the real world. The question remains how to describe spatio-temporal concepts, such as the interaction between disconnected moving objects, adequately within a qualitative calculus and more specifically how to use this in geographical information systems. In this paper, the Basic Qualitative Trajectory Calculus (QTCB) for representing and reasoning about moving objects is presented. QTCB enables comparisons between positions of objects at different time points to be made. The calculus is based on few primitives (i.e., distance and speed constraints), making it elegant and theoretically simple. To clarify the way in which trajectories are represented within QTCB, specific cases of movements (e.g. circular movement) are presented. To illustrate the naturalness of QTC, a ‘predator–prey’ example is studied.