Graphical Abstraction and Progressive Transmission in Internet-based 3D-Geoinformationsystems

In summary, the aim of this research thesis is to fill a gap left by existing 3D GIS: the generation of a meaningful, interactive, three-dimensional presentation of a selected database, especially in terms of the graphical abstraction and progressive transfer in a heterogeneous network environment. The intention here is to expand the concept of an openly distributed GIS infrastructure of the OpenGIS Consortium (OGC) [BüMc96] to three-dimensional geodata. In contrast to previous work such as [Lang99], the main goal is not to depict a virtual landscape and/or an urban region as photorealistically as possible. Rather, the visual processing of the database should strive to support the user’s information needs. In contrast to computer-graphics rendering, in which a geometric model is depicted on a two-dimensional surface in proper perspective, the goal of the visualization is to transmit information to the user [Fole92]. Apart from the actual rendering, this process also requires a selection procedure that decides which elements of a scene contribute to the information content. This kind of visualization is called graphical abstraction. In a heterogeneous network environment, the problem of resource-adaptive data transfer and visualization is second to the graphical abstraction problem. The question is not only how to suitably describe the selected data, but also how to develop an adequate data transfer that presents the viewer with an initial visual result as quickly as possible. Additional data can be transferred later. This progressive data transfer is crucial for the use of 3D data on the Internet [Ross98]. Core concepts and components of the 3D geodata server developed within this thesis are the development of a query-oriented data model for efficient analysis of topological relations in three-dimensional spatial data, and a method for evaluating the relevance of single feature based on a user specific query. Based on this, a method to generate a graphical abstraction of the query result is developed. In order to compress the resulting model, a compression technique for triangle meshes for progressive transmission is invented. These concepts are proofed by a prototypical implementation within a 3D geodata server