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MRTspace – Multi-User 3D Environments using VRML
Dieter W. Fellner, Oliver Jucknath
Department of Computer Science, University of Bonn
fellnerjjucknath@graphics.cs.uni–bonn.de
Abstract: The paper presents an architecture for multi-user interaction in 3D worlds which is based on existing
server technology to handle the communication aspectand on VRML (and its recent extensions)as the presentation
level protocol. To implement multi-user environments we propose the use of the HTTP (Hypertext Transfer
Protocol) to share the static definition of a common room and the IRC (Internet Relay Chat Protocol) to exchange
the dynamic Information between the participants.
Enhanced realism can be achieved by providing physical continuity across WWW links (eg. geometrically seamless
passing through doors), collision detection, solid walls, intuitive movements in 3D environments including the
climbing of stairs.
Our experiences are based on a prototype implementation called MRTSpace, a stand-alone VRML browser which
was designed as a platform to implement experimental extensions to the VRML standard.
Keywords: VRML, IRC, multi user environment, MRT
1 Introduction
Two key points for bringing VRML closer towards the vision of a cyberspace are a more realistic behavior of the
VRML objects together with a multi-user support.
The major problem with most current VRML browsers is the relatively low level of navigation support either
requiring a long training period or resulting in users frequently getting lost in their 3D scene. Users very easily
loose orientation, either by stepping ‘into’ an object (e.g. diving into the ground or ending up between two sides
of a wall) thus making the reset-to-original-viewpoint button the most frequently used one or by the rather sudden
change of the environment when following WWW links.
To give a more realistic feeling of the scene MRTSpace has several levels of collision detection which directly
affect the path of the camera and thus meet the user’s intuitive expectation of solid objects. Controlling the user’s
camera path by methods of distance control and collision detection further introduces a consistent way to ‘walk’
on the ground (i.e. keeping the distance to the ground at a constant value), including the climbing of stairs of the
jumping into ditches.
Furthermore MRTSpace has several heuristics to determine whether a WWW link leads to a continuation of
the current scene, e.g. an adjacent room. In this case MRTSpace loads the new scene, merges it with the current
scene and allows the user a smooth transition from one room into the next. This way, the user can keep track of his
or her position in 3D space, which is one of most important reasons to use a 3D world for navigating the WWW.
Another quite unique feature of MRTSpace is the support of multiple users sharing a single room, with several
ways of interaction, thus leading to the original concept of cyberspace as a means of communication. Thus
MRTSpace merges two technologies: IRC [OR93] as a medium to communicate and VRML [BPP95a] as a
interface to a virtual reality. IRC was originally developed to allow people all over the world to chat with each
other. It has been used to develop a network of servers which form the backbone of a very effective and fault tolerant
multi user medium. Using the HTTP for sharing the constant data of a room where people can meet and using
IRC to exchange information between these users avoids several start up problems that arise when introducing new
specialized servers.