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Abstract-This paper introduces a reasoning system based on a previously developed model for ternary projective relations between spatial objects. The model applies to spatial objects of the kind point and region, is based on basic projective invariants and takes into account the size and shape of the three objects that are involved in a relation. The reasoning system proposes a set of permutation and composition rules, which allow the inference of unknown relations from given ones. I. INTRODUCTIONThe field of Qualitative Spatial Reasoning (QSR) has experienced a great interest in the spatial data handling community due to its potential applications [1]. An important topic in QSR is the definition of reasoning systems on qualitative spatial relations. For example, regarding topological relations, the 9-intersection model [2] provides formal definitions for the relations and a reasoning system based on composition tables [3] establishes a mechanism to find new relations from a set of given ones.As discussed in [4], geometric properties can be subdivided in three groups: topological, projective and metric. Most qualitative relations between spatial objects can be defined in terms of topological or projective properties [5]. Qualitative distances are a qualitative interpretation of metric distances [6].Projective relations are a category of spatial relations that can be described by projective properties of the space without resorting to metric properties [7]. Projective relations are thus qualitative in nature because they do not need exact measures to be explained. Projective relations are more specific than topological relations and can serve as a basis for describing relations that are not captured by topology. At an intermediate rank between metrics and topology, projective relations are as much varied as "right of", "before", "between", "along", "surrounded by", "in front of", "back", "north of", "east of", and so on.To have a common sense understanding of projective relations, it is helpful to think about different two-dimensional views of a three-dimensional real world scene of objects: changing the point of view, metric aspects such distances and angles among the objects appear to be different, but there are properties that are common in all the views. These common properties are projective properties.Likewise topological relations, which are defined by using the connectedness topological invariant, projective relations

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