Representation of Geographic Terrain Surface Using Global Indexing

A global 3D geographic model and a feasible solution for its visualization and management remains a challenging vision. The existence of a reusable platform would provide an unprecedented potential for development of applications related to geography and facilitate comprehension of geographic data. Unlike cartographic maps, 3D models can capture the geometry of geographic features without flattening the environment, without cartographic projection---can avoid geometric distortion. More interestingly, however, 3D models can be composed into a single model spanning the whole world; it can be navigated visually in order to access information and data in the same geometric space as we navigate ourselves in our real environment. This article attempts to narrow down the overhead of problems in visualization of 3D geographic information and intends to identify fundamental issues common to other systems in the domain. Handling entire terrain is inherently coupled with global spatial index. This problem is overviewed and a solution is proposed. Afterwards the data representation of the essential surface in geography is introduced. The representation deals with the problem of LOD and is suitable for use with DBMS. Finally concepts about alteration of terrain data in the database are addressed. The article argues for the introduced solution and is backed with an implementation of a prototype computer system. GLOBAL TERRAIN FOR VIRTUAL GEOGRAPHY Centre for 3D GeoInformation, as well as many other research and development groups around the world, is working on a system for visualization of geographic features in 3D scene. With different proceedings, these efforts stand for an iterative approaching to a technology referred as Digital Earth (Gore, 1998). Digital Earth aims at providing better human user interface (Engelbart, 1962) made of geographic features, which allows a visual navigation in order to increase the capability of a man to approach a complex problem situation in geographic context, to gain comprehension and solution speedier with the possibility of gaining a useful degree of comprehension. Digital Earth would allow accessing the data representing the geographic interface itself as well as arbitrary attributed information---georelated information. Focusing on a method that facilitates construction and maintenance of such geographic 3D model, terrain stands for one of the most significant components. Geometry of the digital terrain provides a surface, which all other geographic features are related to. Put in other words, terrain representation provides the core component in the definition of virtual geography. Terrain is large, continuous, with complex high frequency geometry. Local mathematical approximations of terrain are extremely complex and automated global