Current spatial database systems offer limited querying capabilities beyond topological relations. This paper introduces a model for projective relations between regions to support other qualitative spatial queries. The relations are ternary because they are based on the collinearity invariant of three points under projective geometry. The model is built on a partition of the plane in five regions that are obtained from projective properties of two reference objects: then, by considering the empty/non empty intersections of a primary object with these five regions, the model is able to distinguish between 31 different projective relations.
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