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Chapter 1 - Introduction

1.1 Overview

The goal of this research was to determine an intuitive and efficient approach for facilitating scalable interpersonal communication within the GreenSpace system. To accomplish this, we evaluated the existing methods for communication within large-scale virtual environments and then explored the adaptation of the most promising of those methods to GreenSpace. This thesis document presents the results of that exploration, including a discussion of existing multi-user systems and an evaluation of the prototype communication control system developed through this research.

The rest of this chapter includes background on the GreenSpace project (which this thesis is a small part of), motivation for this topic of research, and a description of the thesis document's organization.

1.2 GreenSpace

The GreenSpace project was born in April of 1993, through discussions between Human Interface Technology Laboratory (HITLab) director Dr. Thomas Furness and Fujitsu Research Institute director Dr. Masahiro Kawahata. They planned for the development and demonstration of "an immersive communication medium" to allow people on both sides of the Pacific ocean, eventually people all over the world, to share experiences in a "virtual common" [Dans94][Jone95].

An immersive computer system is one in which the user's senses are surrounded by computer-generated stimuli that enable a feeling of presence in the simulated environment. Presence is the subjective feeling of actually being in a place, whether it is real, augmented, or virtual [Pulk94]. Users are able to look, listen, navigate, and manipulate objects within the computer generated environment as if they were physically there. Immersive systems are typically called virtual reality (VR) or virtual environment systems, although not all systems that claim to be VR are immersive. Immersion can be accomplished in a number of ways, including combining head-mounted displays (HMDs), position tracking, and high-speed interactive 3D computer graphics.

Rather than have the attendees of a meeting physically travel to a common location, they can use computer networks to meet in a common computer generated immersive environment, or "virtual common".

In November of 1994, the GreenSpace team, led by Paul Danset, simutaneously demonstrated a prelimary test-bed at the NICOGRAPH Convention in Tokyo and the HITLab in Seattle. On four consecutive days, attendees of NICOGRAPH and visitors tothe HITLab participated in trans-Pacific virtual teleconferences (see Figure 1.1).

(Figure)

Figure 1.1: Danset, Kawahata, and Furness in GreenSpace

The software system was developed at the HITLab and was duplicated for the NICOGRAPH site. The hardware setup at each side of the demonstration was nearly homogeneous and included the following:

For various reasons, both in hardware and software, the demonstration was limited to a total of four users at any given time (two at each site). In the future, GreenSpace plans to support over one hundred users at a time, using heterogeneous hardware systems and broadband networks. In order to achieve this, the system software must be scalable to an arbitrary number of users.

The demonstration application was a cooperative game in which the users attempted to herd flying creatures into goals at the corners of their meeting table. Of course, this was a toy application intended to show how people in physically different parts of the world can virtually meet and work together in real-time. Actual applications of the GreenSpace system include collaborative design, virtual space teleconferencing, situational training, and entertainment.

The preliminary testbed used for the demonstration has given the GreenSpace group an opportunity to begin to identify the issues involved in creating a "immersive communication medium." Work is well underway to create a more general GreenSpace software infrastructure to achieve this goal. This thesis will focus on one aspect of that research, interpersonal communication within large-scale mutli-user virtual environments.

1.3 Motivation

During one of the HITLab Consortium meeting demonstrations of VEOS [Bric93], we observed that people in a two-user virtual environment spent more time interacting with each other, even when they had never met before, than they did with the rest of their environment. While there could be many reasons for this, adding additional users to a virtual environment certainly had a profound impact. The infrastructure required for multi-user virtual reality systems is a superset of that required for single-user systems, so it quickly became clear that more research had to be done into the unique aspects of multi-user systems. Tools which enable real-time arbitration, communication, or cooperation are unique to multi-user applications.

The Naval Postgraduate School (NPS), which is home to a premiere multi- user virtual environment research facility led by Michael Zyda, described what they believed to be the important virtual environment research topics to the Computer Science and Telecommunications Board of the National Research Council [Brut95]. Among their conclusions in that report, they claimed that "any workable solution must address scaling up to arbitrary sizes." Indeed, as we move away from single-user environments to multi-user environments, it is not enough to simply add more users. The naive approaches of centralized and distributed communication, do not scale well to an arbitrary number of users [Goss94]. Not only do the servers or networks become overloaded with data being passed between users, but the user's machines can become overwhelmed by a deluge of data from the activities of users that they may not even be interested in. Various techniques have been developed to overcome these limititations, upon which this research will build.

Furthermore, many of the existing tools for interpersonal communication are confined to narrow modes of communication [Suga94]. For instance, the telephone only allows for planned verbal communication. The user must select a person to call and usually the topic to discuss, before establishing communication. Many of the communication modes we take for granted in face-to-face communication, such as body language, are lost with the telephone and other interpersonal communication tools. These narrow bands of communication in traditional teleconferencing tools can present barriers to communicating that make many people fearful or hostile towards the tools themselves, thereby making communication even more difficult [Mill76][Kell85]. According to researchers at the NTT Human Interface Laboratories in Japan, what is needed are tools that provide seamless support for real-time communication and stored data and planned and casual communication, as well as multi-media communication modes [Suga94]. The prototype developed through this research supports these goals.

1.4 Organization

The next chapter describes various Driving Applications, which could benefit from this research and that of the more general GreenSpace project.

The Multi-User Systems chapter examines many existing multi-user communication systems, while searching for useful techniques to apply to GreenSpace.

The Spatial Culling Prototype chapter describes the prototype that was developed through this research and how it relates to existing systems. The design, implementation, and evaluation will be discussed in detail.

Finally we will present some Conclusions about what this research has told us about interpersonal communication within GreenSpace and where future research might lead.

There are two appendices: the GreenSpace Prototype User's Guide, which was made available as an HTML (Hypertext Markup Language) document to users of the system, and the GreenSpace Prototype Survey, which was an online HTML form that users of the system were asked to fill-out.