Suggestions for Extending the OGC Styled Layer Descriptor ( SLD ) Specification into 3 D – Towards Visualization Rules for 3 D City Models

3D city models can be visualized on the web through OGC W3DS services. However this standard does not support a client-side definiton of visualization rules in order to have a homogeneous visualization of 3D scenes representing data from different servers. But for 2D maps on the web this goal is achieved using a specific language [specification]-the Styled Layer Descriptor (SLD) Specification. We present here an extension of the latest version of this specification into 3D as a separate profile and give first examples of implementing this 3D-SLD profile into our W3DS server implementation. 1. MOTIVATION 3D city models are becoming more and more popular. Urban data management benefits from this through a range of new possible applications. But of course this trend needs standards in order to allow interoperability between different cities. 3D visualizations of city or landscape models are being made interoperable by corresponding OGC standards. Standards are also being developed for 3d city models-CityGML seems especially promising regarding the exchange of 3D building models. Typically, within GIS there is a clean cut between raw geodata and visuali-zation properties. This is an advantage because the same data can be used and displayed in multiple ways according to specific needs within each project or of each user. We argue, that this division should also apply to 3d city models. Until recently, in almost all cases the 3d model was already considered as a type of visualization. Typically graphic formats such as DXF, DWG, VRML and other special CAD formats were being used for representing the 3d data. Ideally we believe that it would make more sense if the raw data would only describe the geometry plus the semantic object classes with their respective attributes. This raw data then is completed with visualization rules-as it is the case in 2D GIS. In order to allow this clean cut, a separate format for the visualization regulation should be defined. This then can be applied to the various spatial features in different situations in different ways. This is already the usual way, how it is done for 2d web map. The visualization rules there are being expressed through the OGC Styled Layer Descriptor (SLD) specification. SLD offers many chances in this direction and makes it possible to integrate diverse data sources into a WMS and to style them consistently. It would be great if this would also apply to 3d data representing DEMs, …