General interest in visualizations of digital 3D city models is growing rapidly, and several applications are available that display such models realistically. Many authors have emphasized the importance of realistic illumination for computer generated images, and this applies especially to 3D city visualization. However, current 3D city visualization applications rarely implement techniques for achieving realistic illumination, in particular the effects caused by current weather. At most, some geospatial visualization systems render artificial skies – sometimes with a georeferenced determination of the sun position – to give the user the notion of a real sky.

In this chapter we present techniques to augment visualizations of digital 3D city models with real-time display of georeferenced weather effects. For this purpose we retrieve weather information from different sources, i. e., real-time images from cameras and radar data from web-based weather services. We use this knowledge in the rendering process for realistic visualization of different weather-related issues, such as clouds, rain, fog, etc. Our approach is not limited to a specific setup, and we have evaluated the results in a user study presented in this chapter.