19th 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.