关键词: 三维建筑综合, 多尺度表达, 空间数据管理, 空间索引, GAMR树

Abstract:

With the rapid development of geographical information acquisitions methods, 3D city models are widely used now. Level of detail (LOD) is used to improve the performance of three-dimensional (3D) visualization. Management of multi-scale building data is important in 3D building generalization, and many scholars have studied the indexing model of multi-scale spatial data for 2D map. In order to satisfy the demands of massive spatial data in 3D city modeling, a new spatial indexing model named as GAMR tree (Generalization Area Multi-representation R Tree) is proposed to deal with the multi-scale model of 3D building. Based on the characteristics of 3D building generalization, impact factors for constructing the 3D building generalization areas are analyzed in this paper. Next, the generalization areas are divided into four types which are denoted as big city, city, town and village. As a result, different generalization methods are adopted for the generalization of different areas. In this research, GAMR tree is defined based on the structure of R-Tree while assigned with different node types. Two indexing trees, which are named respectively as the generalization R tree and the child tree of generalization area, are included in the new indexing model. The leaf node of the child tree is consisted of two items, one is the MBR that representing the building ground area, and the other is the corresponding 3D building model for that area. While the branch node is consist of a MBR that accounts for the total area of its child nodes, and pointers that connect to its child nodes. The children trees are generated by a bottom-up method, and the height of a tree is determined by the threshold calculated in generalization. Multi-scale querying method of GAMR tree is furthermore proposed in this paper, and the steps of a rectangle querying instance are presented. Considering the variations of projected length caused by different sight directions, the corresponding LODs of building models that organized by GAMR tree is well determined and chosen to be displayed on the screen, so that the projection of building features can be recognized by users. Generally, the experiment has proved that this spatial indexing tree works well in 3D building generalization and multi-scale representation.

Key words: 3D building generalization, multi-scale representation, spatial data management, spatial index, GAMR tree