2004 
STUDY ON WEB-BASED DISTRIBUTED VIRTUAL CITY ENVIRONMENT 
Jing CHEN“, Jiansi YANG”, Qingquan LI* 
"LIESMARS, Wuhan University, 129 Luoyu Road, Wuhan, 430079, P.R.China, jehen@wtusm.edu.cn 
"School of Urban Studies, Wuhan University, Wuhan, 430072 P.R.China, 
Working Group IV/2 
KEY WORDS: Web-based, Visualization, Distributed, Internet, Networks 
ABSTRACT: 
Web-based 3D GIS becomes one of the major areas of GIS research, which extend distributed virtual geographic environment when 
integrated with virtual reality. Distributed virtual city environment, one of the most important research fields, will meet the demands 
of the urban planning and urban landscape. Firstly, a CORBA-based distributed architecture is presented. Secondly, a new 3D LOD 
building model, which can be used to create multi-resolution building data, is proposed. Next, the message for managing multi-user's 
interaction and the change of virtual city scene are designed to maintain the scene's consistency Finally, a web-based virtual city 
environments system to visualize 3D city scene and create the user's avatar is developed. 
1. INTRODUCTION 
n recent years, with the development of technologies of the 
computer graphics and computer-human interface, there are 
some research works to explore the integration of 3D GIS and 
virtual reality (VR), which is called a new kind of geographical 
information systems, Virtual GIS. (Peter Berger et al 1994, 
Pajarola R B ert al 1994, Pajarola R B et a/ 1998, Faust et al 
2000, Edmund SIDES 2000,LIU Zhan-ping et al, 2002). 
In most of these researches, web-based Systems mainly use 
virtual reality modelling language (VRML) and adopt 
traditional two-tiered Browser/Server pattern in terms of 
system architecture (Siyka Zlatanova 1999). But these methods 
and systems are not efficient in dealing with multi-user 
interactive operation and browsing massive 3D city model data. 
Because of the massive 3D city data and complicate structure 
of 3D city models (Wang. X H, Gruen A, 1998+ Sun min, 
Chen June 4999+ fj Qingquan, Yang Bisheng 2000), it needs 
so many vector data and texture data to construct 3D city scene. 
So it is difficult to improve the speed of 3D roaming and to 
reduce the data volume of 3D rendering. Level-of-Detail (LOD) 
model is an efficient method, which can be used to improve the 
speed of 3D roaming and reduce the data volume of 3D 
rendering. Based on the discussions of requirement of 3D 
building model, the view-dependent LOD method is 
development to solve the problem. 
In this virtual city environment users can see the avatar of other 
users and interact with cach other. They can make operations 
on the buildings such as removes add and query . If one 
building has been removed, all users can also sce the change of 
city scene. So the message-based method is presented to 
Manage multi-users and the change of virtual city scene are 
Proposed to maintain the scene's consistency. 
The following sections are arranged as follow. Firstly, a 
distributed system architecture, which is based on CORBA, is 
Presented. Secondly, a new 3D LOD building model, which 
N be used to create multi-resolution building data, is 
1133 
proposed and a view-dependent 3D fast roaming method is 
developed. Next, the message for managing multi-users 
interaction and the change of virtual city scene are designed to 
maintain the scene’s consistency Finally, a web-based virtual 
city environments system to visualize 3D city scene and create 
the user’s avatar is developed, and several results are illustrated. 
2. WEB-BASED DISTRIBUTED ARCHITECTURE 
With the development of distributed computation, a web-based 
geographic information system (Web GIS) has been 
strengthened in system reliability, efficiency, resource sharing, 
and flexibility for incremental system growth. Compared with 
a centralized GIS, a distributed Web GIS can meet user’s 
organizational objectives better. It is possible to provide 
distributed geographical information to some application, such 
as 3D city landscape, real estate management. However, an 
important characteristic of large computer networks such as the 
Internet, the World Wide Web (WWW), and corporate 
intranets is that they are heterogeneous. In particular, the 
development of Web GIS applications and components that 
support and make efficient use of heterogeneous networked 
systems is very challenging. 
2.1 CORBA 
CORBA, developed by The Object Management Group 
(OMG), is an industry standard for distributed heterogeneous 
system. The recent new version of CORBA, Version3.0, was 
officially published in 2002. To deal with heterogeneity, 
CORBA is defined by a neutral Interface Definition Language 
(IDL), which can be used to specify a component's contractual 
interfaces with potential clients. It enables client and server 
objects to interoperate across networks and operating systems. 
The architecture of CORBA consists of four main 
components :(1) an Object Request Broker (ORB), (2) 
Common Object Services, (3) Common Facilities. and 4) 
Application Objects. The Common Object Services and 
Common Facilities are provided by a group of objects on the