CityGML is an open data model and XML-based format for the storage and exchange of virtual 3D city models. It is realised as an application schema for the Geography Markup Language 3 (GML3), the extendible international standard for spatial data exchange issued by the Open Geospatial Consortium (OGC) and the ISO TC211. CityGML is intended to become an open standard and therefore can be used free of charge.
CityGML is specially supported by the aristoteles viewer. There is a previously learned model for its namespace available. This reduces the risk of unpropper mappings and provides a first relativly complete aristoteles schema, what will decrease the loading time for CityGML-files.
There is also a support for the CityGML specific appearance model within the TexturedSurface elements. There is a mapping within the mapping definition file appearance.xml available!
http://www.ikg.uni-bonn.de/sig3d/pilot3d/
http://www.citygml.org/ project homepage
http://www.ikg.uni-bonn.de/sig3d/ working group homepage