Integrating Levels of Detail in a Web-based 3D-GIS

3D spatial data are of increasing interest in urban areas. Especially the WWW offers new applications areas for communication and interaction between planners and concerned citizens and clients. Using a data model which supports both 3D geometry and 3D topology we have developed a 3D-GIS including a web-based user interface implemented in Java and VRML. However, handling a large data amount of 3D city models is critical. Therefore we are using several levels of detail for visualization. But in a distributed environment, especially in web-based applications, not only the rendering time is critical but also the data transfer time. In our web-based approach, geo-objects are transmitted in the same level-of-detail which is used for visualization. Further details are loaded when they are needed while the user explores the scene. Additionally we have extended the transfer protocol sending the VRML scene step by step giving the user an impression of the scene as fast as possible.