A MIX GLOBAL DATA STRUCTURE BASED ON QTM AND VORONOI

To efficiently store, retrieve and update the global spatial data, a hierarchical and dynamic data model on a global scale is urgently needed. The QTM (Quaternary Triangular Mesh) as a hierarchical quadtree data structure on sphere is one of the most efficient methods for managing the global spatial data in many applications. But QTM structure is based on fields instead of objects. So it is efficient in multi-resolution manipulation, but difficult in local data update frequency. To efficiently manipulate multi-resolution and to update data dynamically, a mix global data structure-----Variable Tree Data Structure (VTDS) is designed. There are two different types of ‘node’s in VTDS, one is ‘O_Node’ (i.e. object-node), the other is ‘I_Node’ (i.e. index-node). At every level (except the root one), all ‘O_Node’s only consist of spatial objects represented by QTM address codes which is efficient in multi-resolutions manipulation. However, ‘I_Node’s may consist of child ‘O_Node’s and ‘I_Nnode’s which include indexing information by which the interested objects within a location scope can be retrieved easily. Meanwhile, the Voronoi diagram based on QTM of related objects at a given level will be dynamically generated to preserve adjacency relationships, which are fundamental to perform queries and updates in local addition or deletion of individual objects. Multi-resolutions manipulation and dynamic update of spherical objects in VTDS are given in details in this paper.