Modelling for 3d Gis: Spatial Analysis and Visualisation through the Web

The paper presents an integrative approach to 3D modelling of complex scenes of determinate objects. The key characteristics of the proposed data model are support of 3D geometry and topology for extended spatial analysis, and facilitating interactive visualisation. The model supports the four geometric abstractions of spatial objects, i.e. point, line, surface and body. The representation based on two constructive elements (nodes and faces) is sufficient for the derivation of a large number of 3D topological relationships. The restrictions imposed on faces (connectivity, convexity, ordering) as well as the supplementary information maintained per object (radiometric parameters, behaviour) ensure the correct rendering and enable the design of realistic (photo textured), dynamic 3D worlds. The user interaction with the database residing on the Web relies on standard Internet tools — CGI scripting, VRML and HTML documents. The description of our prototype system for querying, visualising, and communicating with a DMBS is supported by several examples. The designed model is successfully linked to developed procedures for data collection. Using a digital photogrammetric system we can collect semi-automatically geometric and semantic data, and automatically extract texture from aerial photographs as necessary for texture mapping of roof facets or texture draping over the ground surface. We consider the approach a good step forward to an operational urban 3D GIS.