19^th International CODATA Conference
Category: Data Visualization

Structures for virtual cities

Hrivnak Jan, Mgr (hrivnj1@fel.cvut.cz)
Chludil Jiri, Ing (xchludil@fel.cvut.cz)
Czech Republic

Our research is focused to realistic visualization of urban structures in virtual reality. We are interested in developing data structures for effective and transparent representation of virtual cities and additional effects for more realistic visualization. Our data structure is inherited from IFC (Industry Foundation Classes) ISO standard from IAI (International Alliance for Interoperability). We choice for testing an environment of third party application named Virtual Old Prague originally developed by students of Charles University in 1999. Our current work has been aimed to the integration of influence of a sunray on buildings facade depended on time and season. The main problem of this and other similar applications is non-transparent representation of stored data. The structure of these data is optimized to fast visualization without respect to general understandability. This fact makes difficult to extract and analyze necessary information for a new functionality like weather conditions. Therefore we have reorganized inner data structure to the transparent and standard IFC model.  structure of IFC model enables to recognize meaning of every data element and to relate it with relevant meta-information. The application, suitable for supporting of IFC model, is jXpress (developed for MUMMY project IST 2001-37365) Weather conditions mainly present the playing with shadows. To compute shadows of buildings, we have implemented a method based on scene projection on polygonal face. The result is a polygonal shape representing a superposition of several shadows. The shadow area is combined with the original texture using the alpha blending. The analogical approach was used for displaying color of sunrays on the same texture. Complicated and thus lazy access to required data was the main trouble to reorganize data structure in given implementation. Presented approach solves these troubles. Our approach allows effortless and clear access to the whole information about cities without difficult analysis, and thus it facilitates simple integration of any new functionality to virtual environment.