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In geographic space, there are there main spatial relations among spatial entities, which are topological relation, direction relation and distance relation. Because spatial relation theories and researches directly influence the design, develop and application of GIS system, it attaches greatly importance to international GIS and interrelated academe. Qualitative spatial reasoning forms an important part of the commonsense reasoning required for building intelligent GIS. Because of the complexity and uncertainty inherent in spatial issues, the description and reasoning of spatial relation often use qualitative method in accordance with spatial cognition. Because direction relation is one of the most frequent qualitative spatial reasoning factors used in everyday life, the qualitative direction relation reasoning is a kind of important qualitative spatial reasoning. In this paper, we focus our efforts on the problem of reasoning the direction relation between regions that are composed of sets of polygons. According to the number of direction relation elements, direction relation can be divided into monomial direction relation (including one direction relation element only) and multinomial direction relation (including more than one direction relation elements); and the reference frame of direction relation can be divided into one reference frame and two reference frames. Previous methods always abstract regions into points or approximately equal in their size under two reference frames. In order to have meticulously reasoning results, we proposed a method of qualitative spatial reasoning for direction relation based on one reference frame under four different kinds of situations, that is monomial and monomial direction relation reasoning, multinomial and monomial direction relation reasoning, monomial and multinomial direction relation reasoning, multinomial and multinomial direction relation reasoning. In addition, a prototype system and a case study are carried out, and the future research problems and directions about qualitative spatial reasoning for direction relation are also discussed.
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