Spatial directional relation is an important content of spatial relation research, but its fundamental theories were still not perfect; most of the relevant references gave their emphasis to formal description models of directional relation but neglected the fundamental theories system based on directional relation itself. To make deeper investigation into the issue, this paper in detail proposes definition, reference frame, properties, influence factors, and classification of directional relation; these conceptual issues provide theory basis for formal description models of directional relation and applications of relevant research.
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