Interactive visualization of large-scale geographic data

Abstract

Geographic information systems progress strongly in a lot of different application domains. In addition, the gathering of geographic information is inevitable and large-scale geographic databases and server infrastructures need to handle this amount of data. Geographic data is growing in precision and complexity, so that it is necessary to explore and analyse datasets in an interactive way. Interactive visualization is key to explore geographic data sets and therefore indispensable for everyone using geographic data. In the following, new ways for interactive rendering techniques are presented to handle the challenges in nowadays large- scale geographic information systems. The thesis starts with an introduction to geographic information systems followed by an analysis of requirements and challenges for geographic visualization systems and virtual globe systems. Furthermore, an introduction to the rendering pipeline is presented. To face the challenges of today’s geographic visualization systems we introduce the GlobeEngine framework which enables a modular structure for rapid prototyping of geographic visualization applications and also contains all running prototypes of this work. The main algorithmic contribution of this thesis is new rendering techniques, namely a new version of the RASTeR terrain engine, an innovative technique for rendering vector maps for interactive terrain and map visualizations and a novel graph bundling technique using vector maps as basis for bundling paths in an interactive 3D perspective environment. Terrain visualization is the basis for an interactive 3D geographic visualization system. However, it is hard for decision-makers to clearly identify the best choice of terrain rendering algorithms. Therefore, this work provides an overview over terrain rendering requirements and existing terrain rendering solutions as well as their applicability to modern graphics systems. Furthermore, this thesis shows how RASTeR can be adapted to modern graphics hardware and a set of terrain visualization features, such as edge highlighting, ambient occlusion or terrain slope, aspect and flow visualizations to extend the capabilities of the existing terrain visualization. Often, vector map visualizations are used on top of 3D terrain rendering. In- interactive rendering of large-scale vector maps is a key challenge for high-quality geographic visualization software systems. This thesis contains a novel approach for the visualization of large-scale vector maps over detailed height-field terrains. This method uses a deferred line shading approach to render large-scale vector maps directly in a screen-space shading stage over a terrain visualization. The fact that there is no traditional geometric polygonal rendering involved allows our algorithm to outperform conventional vector map rendering algorithms for geographic information systems. A flexible clustered deferred line rendering approach allows a user to interactively customize and apply advanced vector styling methods, as well as the integration into a vector map level-of-detail system. Dense line graphs and polyline maps are challenging for interactive visualization in geographic information systems. Bundling techniques are a common approach to reduce clutter and have successfully been demonstrated for the display of complex planar graphs. Previous techniques typically applied some forms of attraction or repulsion forces to bundle edges. In geographic visualizations, it is often necessary to take the semantic information into account and constrain path bundles to follow some reference network vector map. This thesis applies a novel method which uses geographic vector map reference information to route, visualize and simplify path bundles along their network paths in a constrained environment using adaptive B-splines. The thesis is concluded by a summary and a future work section presenting future research topics.