In recent years, most virtual 3D city models have been realised as purely graphical or geometrical models, neglecting the semantic and topological aspects. Thus, these models could almost only be used for visualization purposes but not for thematic queries, analysis tasks, or spatial data mining. Since the limited reusability of models inhibits the broader use of 3D city models, a more general modeling approach had to be taken in order to satisfy the information needs of the various application fields.
CityGML is being developed since 2002 by the members of the Special Interest Group 3D (SIG 3D) of the initiative Geodata Infrastructure North-Rhine Westphalia (GDI NRW) in Germany. The SIG 3D is an open group consisting of more than 70 companies, municipalities, and research institutions working on the development and commercial exploitation of interoperable 3D models and geovisualization. Another recent working result of the SIG 3D is the proposition of the Web 3D Service (W3DS), a 3D portrayal service that is now being discussed in the Open Geospatial Consortium (OGC Doc.No. 05-002).
The aim of the development of CityGML is to reach a common definition of the basic entities, attributes, and relations that can be shared over different applications. This is especially important with respect to the cost-effective sustainable maintenance of 3D city models, allowing to sell the same data to customers from different application fields. The targeted application areas explicitly include city planning, architectural design, touristic and leisure activities, environmental simulation, mobile telecommunication, disaster management, homeland security, vehicle and pedestrian navigation, and training simulators.
To provide (only some) names of bodies working on and supporting CityGML: municipalities of Berlin, Hamburg, Cologne, Düsseldorf, Recklinghausen, Leverkusen; British Ordnance Survey, State Mapping Agency of North-Rhine Westphalia; companies T-Mobile, Rheinmetall Defence Electronics, Snowflake, CPA Geo-Information, GIStec, 3D Geo; research institutions: Universities of Bonn, Potsdam, Dortmund, Applied Sciences Stuttgart; Research Centre Karlsruhe, Fraunhofer Institute for Graphics Research.
What are the future plans?
We have started to discuss CityGML on an international level both within EuroSDR and OGC and intend to make it an OGC approved application schema for 3D city models. Further developments beyond V1.0 might address dynamic features (e.g. moving objects, water tides), time and history, inclusion of curved lines and surfaces, and possibly the incorporation of the geometric modeling principle of Constructive Solid Geometry. Also the development of a "Simple CityGML profile" (based on the GML simple features profile) was proposed to confine the requirements on software systems.