3d Urban Gis on the Web: Data Structuring and Visualization

The maintenance, visualization and query of 3D urban data has always been problematic due to the complexity of geometry, diversity of attribute information, large amounts of data, demanded comprehensive analysis and queries requiring new techniques for visualization and query. The approach presented here aims visualization and query via Internet and utilizes established standards and techniques to access and retrieve remote data: Virtual Reality Modeling Language (VRML) and Hypertext Markup Language (HTML) to visualize respectively 3D geometry and text information, Javascript and Common Gateway Interface (CGI) scripts to control the interaction and query of the three dimensional Geographic Information Systems (3D GIS) on the Web. The paper focuses a couple of aspects related to the data base structure on the GIS server: clarification of data needed to create VRML and HTML documents, and data structuring according to an elaborated classification of the information stored per object, i.e. attributes, connections (relationships) and functions (behavior), considering its thematic and geometric aspect. A data structure capable to serve spatial analysis and to supply data for a VRML document creation with ability to introduce and control dynamics of objects, is presented. Issues related to fast navigation trough the 3D model, i.e. a mechanism to build LOD without storage of extra information are discussed and some results of the usage of a R-tree structure to create Levels of Detail (LOD) are reported.