The triangulated irregular network (TIN) provides a versatile and widely used approach to representing terrain models in a way that retains the original sample points, adapts to variation in data density and incorporates linear features corresponding to natural or man-made phenomena. Classification of the scale-related priority of the constituent points and linear features can be used to create hierarchical, multiresolution TIN representations. A large proportion of the data items included in conventional and hierarchical TIN data structures are concerned with recording the topology of the triangulation. Although TINs typically use many fewer points than the main alternative representation of regular rectangular grids, they do not usually occupy much less data storage, due to the topological data. This paper describes a novel multiresolution storage scheme which uses an approach termed the Implicit TIN, in which storage requirements are reduced significantly by storing only the vertices and constraining features. TIN topology is reconstructed by a procedure when required. The Implicit TIN storage scheme has been demonstrated in the context of an experimental multiscale database. Variable-scale access is provided to polygonal regions of a terrain model which includes polygon, line and point objects that constrain the constructed triangulated model.
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