Analysis and Visualization Techniques for Virtual 3D City Models as Tools for Decision Support
Virtual 3D city models are essential tools for effective communication and management of complex, tree-dimensional urban information. While an increasing number of applications and systems use virtual 3D city models to integrate, process and visualize such data, their potential for decision support is still not fully exploited. In recent years geographic information systems increasingly provide basic 3D functionality, but still lack holistic support of 3D. This thesis presents concepts and techniques for the application of virtual 3D city models as a tool for decision support. Three particular areas of application are examined in detail: as a computational tool for spatial analysis, for the visualization of thematic spatial information, and for immersive visualization of urban models and scenes. First, this thesis presents the image-based analysis technique (Chapter 3) – a novel method for discrete image-based 3D analysis of virtual 3D city models. This technique is based on the detection and evaluation of properties and relationships between 3D objects (e.g., object identity, visibility, distance, and orientation) and can be efficiently implemented using the programmable rendering pipeline. The results of such an analysis facilitate, for example, a quantitative comparison of alternative proposals or a quantitative assessment of potential sites. To illustrate the manifold application fields of this technique two concrete use cases are presented: a solar potential analysis for photovoltaic systems and a visibility analysis of landmarks for assistance in pedestrian navigation systems.
The second part of this thesis (Chapter 4) surveys techniques for visualization of thematic information using virtual 3D city models. The visualization of thematic information is essential for their effective communication. This thesis focuses on surface-related spatial data, which is usually visualized using color-coded surface textures; this emphasizes the spatial relation of the data to the object surfaces. In this process, it is necessary to maintain the structural and topological information of the model in the generated images without modifying the color-coded information. For this purpose, different rendering techniques, such as edge enhancement and façade abstraction, can be utilized. A user study was conducted to evaluate the suitability of these techniques for the visualization of thematic information. The results of this study are presented and discussed.
In the third part of the thesis (Chapter 5) a system for fully immersive visualization of virtual 3D city models is presented. Fully immersive visualization enables the presentation of virtual 3D city models on a 1:1 scale, which emphasizes the communication of the model especially from every-day perspectives, e.g. pedestrian perspective. Thus, immersive visualization offers an intuitive access to and an effective way of realizing, exploring, and analyzing virtual 3D city models. Using the presented visualization system stakeholders can explore and examine different alternatives of an urban project „in situ“ and discuss and evaluate its impact. Fully-immersive visualization impose several conceptual and technical challenges, which were identified and managed during the development of the presented visualization system, including specific enhancements of the 3D rendering process, immersion-aware, assistive 3D camera system, and a synthetic, immersion-supporting soundscape.
This thesis illustrates how virtual 3D city models can be used to assist answering spatial questions. The presented concepts and techniques demonstrate the manifold potential application fields of virtual 3D city models in the decision-making process.