Proceedings of East-West-Vision 2002, Graz, Austria, pp. 99-108, ISBN 3-85403-163-7 ON THE COMPLEXITY OF WEB-BASED PRESENTATIONS OF LARGE URBAN SCENES Jiri Zara 1 ) Abstract The paper analyses requirements on virtual urban scenes presented on the web. Basic principles and methods for data preparation and processing are introduced. Several useful and practical approaches are shown on examples taken from one real implementation of a virtual city – the Virtual Old Prague project. The paper explains why complex virtual cities are still missing on the web and shows ways how to extend already existing web sites by three-dimensional urban objects. 1. Introduction A web presentation of existing urban scenes (cities) seems to be currently a challenging task for many researchers and practical programmers. Indeed, every bigger city in the world operates its own web pages with 2D city layout (maps), photographs of important places and buildings, guides for visitors, and other useful information. Several web sites contain 3D panoramic views in QuickTime VR format. Some other offer single virtual models of selected historical or modern buildings, typically in VRML format. Only a few cities (like Paris [16]) have created larger urban areas offering a walk-through a virtual space bigger than one street or a square. Huge, web-based, interactive three-dimensional presentations of existing urban environments with high informative value are still missing. This paper presents a list of typical requirements on virtual cities. It is shown that the virtual city is not only a collection of 3D models, but it should be a complex information database matching up to a wide range of visitors’ needs. The optimal model of a virtual city should be a common framework for different kind of information, where the virtual reality (or 3D graphics) is just one part of them. We consider a virtual city as a big crossroad of hyper linked information in form of text, images, multimedia, and virtual reality. The last topic is the most promising but also the most difficult part, thus we discuss it here in more details. Presented problems and possible ways to their solutions are documented by examples taken from the Virtual Old Prague project [17]. The first version of this application has been finished in 2001 (see Fig. 1). It is considered as the first running complex virtual city presentation on the web allowing continuous walking through a model stored in a remote database. The data are progressively transferred from the server according to a visitor’s position. A model is theoretically unbounded, i.e. it is scaleable in terms of amount of data describing the city, speed of the network, and rendering performance [21]. 1 Department of Computer Science & Engineering, Czech Technical University in Prague, Karlovo nam. 13, 121 35, Prague 2, Czech Republic, <zara@fel.cvut.cz>.