The Vmo-tree: a Dynamic Spatial Data Model for M a P S

This paper describes an object-oriented approach to model a set of 2D vector data, depicting points, lines, and polygons. These primitive spatial objects are embedded in the Euclidean space with the dynamic Voronoi diagram. A spatial object condensation technique is used to partition the Voronoi diagram into smaller subspaces. Each subspace defines a bounded complex object and constitutes a node of the VMO-Tree (Voronoi based Map Object Tree), a novel data model describing relationships of condensed objects. The VMO-Tree can be constructed by either top-down partition, bottom-up aggregation, or combination of the two. Features of the VMO-Tree include: representing spatial objects in different levels of detail; node containing topologically structured complex objects, some of them child nodes; being able to search vertically between nodes of the tree and to navigate horizontally in each node in a seamless fashion; loading and down-loading spatial objects contained in a node dynamically; complex objects in the tree are independent map sheets and can be operated on separately; each map sheet corresponds to a disk page and has a minimized memory occupation.