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SHARED SPACES: TRANSPORTATION, ARTIFICIALITY, AND SPATIALITY Steve Benford, Chris Brown, Gail Reynard and Chris Greenhalgh Department of Computer Science The University of Nottingham Nottingham NG7 2RD, UK. E-mail: {sdb, ccb, gtr, cmg}@cs.nott.ac.uk

ABSTRACT

We begin by reviewing current spatial approaches to CSCW (mediaspaces, spatial video conferencing, collaborative virtual environments and telepresence applications) and classifying them along the proposed dimensions of transportation, artificiality and spatiality. This classification leads us to identify new shared space applications; so called mixed realities. We present an example of a mixed reality called the Internet Foyer, an application which provides a unified entry point into an organisation's physical and electronic environments and which supports awareness and chance encounters between the occupants of physical and synthetic space. INTRODUCTION

Interest in spatial approaches to CSCW has grown over recent years. Specific examples of the spatial approach include media spaces [2], spatially oriented video conferencing [12, 13, 19], collaborative virtual environments [1, 24] and tele-presence systems [14]. There has recently been some debate as to the relationship between these various technologies and of their underlying interpretations of shared space (e.g. the panel held at ECSCW'95). This paper aims to contribute to this debate in two ways. First, it will undertake a review and classification of these various approaches along the proposed dimensions of transportation, artificiality and spatiality. Second, it will use this classification as a vehicle for introducing the idea of mixed realities; shared spaces which span the synthetic and physical worlds to equal degrees. This will be illustrated through a specific example, The Internet Foyer, a collaborative application which provides a common entry point into an organisation, spanning both its physical and electronic manifestations (i.e. which extends the current notion of foyers in physical buildings to include a representation of the entry point into an organisation's network space). SPATIAL APPROACHES TO CSCW

There has been an explosion of interest in spatial approaches to CSCW over the past few years, albeit from Permission to copy without fee all or part of this material is granted provided that the copies are not made or distributed for commercial advantage, the ACM copyright notice and the title of the publication and its date appear, and notice is given that copying is by permission of the Association for Computing Machinery. To copy otherwise, or to republish, requires a fee and/or specific permission.

a number of different perspectives. These approaches have been motivated by a range of issues which are seen as being important to cooperative work. These include: Persistence and on-going activity - the observation t human co-operation may take place over long periods of time and may involve many inter-related instances of different cooperative activities. Spatial approaches attempt to support this by providing a sense of place, the creation of explicit, familiar and persistent environments within which co-operative work can be situated. Peripheral awareness - the recognition that, even in the most formal of situations such as safety-critical control rooms [10,11], it is important that participants can establish a general awareness of what others are doing beyond their current focused activity. Implicit in the notion of peripheral awareness is the idea of having a periphery - an inherently spatial concept. Navigation and chance encounters - the observation so-called informal communication plays a vital role in establishing and maintaining co-operative relationships (e.g. the notion of social browsing which motivated the development of early mediaspaces such as Cruiser [17]). Spatial approaches attempt to support this issue through the notion of navigation within a shared spatial setting. Usability through natural metaphors - an attemp exploit people's natural understanding of the physical world, including spatial factors in perception and navigation, as well as general familiarity with common spatial environments, in order to construct cooperative systems which can be more easily learned and used (e.g. the frequent use of the Virtual Office metaphor [4]). In a more general sense, spatial approaches to CSCW might be viewed as a shift of focus towards supporting the context within which work takes place, rather than the process of the work itself. Thus, the spatial approach contrasts with other more process-oriented approaches to CSCW (e.g. that of workflow systems) and might even be seen as a general reaction to the criticisms levelled at process models in recent years (see [22, 25]). A brief review of spatial approaches to CSCW

A review of the CSCW literature suggests to us that spatial approaches to CSCW can be grouped into four general categories: mediaspaces, spatial videoconferencing, collaborative virtual environments and telepresence systems. The following paragraphs briefly introduce each of these in turn.

Collaborative Virtual Environments Collaborative Virtual Environments (CVEs) involve the use of networked virtual reality systems to support group work [1]. The key concept behind CVEs is that of shared virtual worlds: computer generated spaces whose occupants are represented to one another in graphical form and can control their own viewpoints and can interact with each other and with various representations of data and computer programs. CVE technology is less mature than either the video conferencing or mediaspace technologies. However, a number of representative examples can be found such as the DIVE system from the Swedish Institute of Computer Science [6], the Collaborative Workspace from NTT [24], our own MASSIVE system [9] and large-scale military simulations such as NPSNET [26].

Media spaces Mediaspaces involve the enhancement of existing workspaces (typically offices) with integrated audio/video communication facilities as a basis for providing a range of general communication services [2]. In contrast to multimedia conferencing systems, mediaspaces focus on support for social browsing, peripheral awareness and the establishment and maintenance of long-term working relationships between physically separated people. Typical services include the ability to glance into other people's offices or to establish longer term office share relationships via open connections. The best known examples of mediaspaces include Cruiser [17], a system to support social browsing by touring through various offices and public spaces, and RAVE [8], a system to enhance peripheral awareness of on-going activity and also to establish long term working relationships. Mediaspaces have emerged as an area of CSCW in their own right and several authors have provided theoretical or experimental evaluations of the technology, mostly focusing on problems with video communications such as limited field of view and lack of navigation [7].

The essence of CVEs is that the shared space defines a consistent and common spatial frame of reference. In other words, there is a well established co-ordinate system in which the relative positions and orientations of different objects can be measured. This is then combined with support for independent viewpoints which are represented through embodiments so that it is possible to infer where someone is attending and what they are seeing from their representation (note that making such an inference is not the same as actually seeing what they are seeing). Finally, CVEs aim to provide an integrated, explicit and persistent context for co-operation which combines both the participants and their information into a common display space (in contrast to multimedia systems which typically display communication and data in separate windows). Furthermore, the possibility of including a wide variety of data representations creates the potential to support a broad range of co-operative applications such as training, visualisation, simulation, design and entertainment.

Spatial video conferencing Video conferencing involves the use of combined video and audio communications to support meetings and is now gaining widespread acceptance as a commercial service both in desktop mode (i.e. using multimedia workstations) and also through dedicated links between public meeting rooms. Advanced systems may include communication tools such as shared document editors.

A problem with traditional video conferencing systems is that they do not support any notion of spatial referencing, especially gaze direction whereby participants can infer who is attending to who at any moment in time from their representations. Gaze direction has been identified as a key element of conversation management [18] and other research has indicated the general importance of understanding the viewpoints of others when engaged in collaborative work (e.g. the experiments of Shu and Flowers on viewpoint representation in collaborative design tasks [20]). However, if one looks at the camera in a video conference, one appears to gaze at all of the participants simultaneously; there is no way for other participants to distinguish at whom one is gazing.

Systems for telepresence The concept of telepresence involves allowing remote users to experience a remote physical space through computer and communications technologies. This may involve the ability for the remote participant to view the space, to navigate the space and even to interact with objects in the space. Telepresence applications typically involve the creation of a physical proxy of the remote person in the form of a robot which has cameras attached to it and which may be able to move through the physical environment to varying degrees [21]. In some cases the remote user may actually experience the physical space through the same kinds of immersive technology as is used in collaborative virtual environments, except that in this case, live video is displayed in the headmounted display instead of 3-D graphics. Telepresence is a field of research in its own right with applications focusing on areas such as control of remote robots in hazardous or inaccessible environments (including tele-surgery!) and navigation through remote regions using mobile robots. However, telepresence applications are now beginning to be discussed in the context of CSCW in systems such as the GestureCam [14] which explore the notion of remote surrogates in cooperative work.

Several researchers have recognised this problem and have tried to introduce support for gaze into video conferencing. For example, the Hydra system utilised an arrangement of miniature televisions on a table top to give each participant a consistent representation of gaze [19] and the MAJIC system used video projection techniques to achieve the same effect for three participant meetings [12]. As a slightly different example, the Clearboard system demonstrated the integration of two video streams and a shared drawing surface into a spatially consistent environment in order to support two person design meetings [13]. However, it should be noted that a generalised solution which works well for larger numbers of participants or meetings where participants dynamically join and leave has yet to emerge; the above systems would require considerable physical hardware reconfiguration if this were to happen.

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Underpinning this dimension is a technological distinction. Video technology naturally naturally lends itself to the capture and reproduction of physical scenes, while 3-D graphics naturally lends itself to the synthesis of abstract scenes. However, within this general trend, more elaborate video manipulation technology can warp video signals away from the physical, while scene analysis techniques and real-world data capture can provide the basic data for generating 3-D graphical scenes which correspond directly to physical reality.

A COMPARISON OF THESE APPROACHES

We will now compare these different spatial approaches against one another. This comparison has two main goals: to develop and apply a suitable classification scheme in order to uncover interesting relationships between the approaches and to use the completed classification as a means of identifying gaps where new spatial approaches and applications might be created. Our comparison proceeds in two stages. First, we locate the approaches and systems along the two dimensions of transportation and artificiality. The dimension transportation concerns the extent to which users perceive that they have left behind their local space and have entered into some new remote space. The dimension of artificiality concerns the extent to which the space is either synthetic or is based on the physical world. The second stage of our comparison is to locate them along the further dimension of spatiality; the degree to which they support key spatial properties such as containment, topology, navigation and a shared frame of reference. We begin by introducing the dimensions of transportation and artificiality which we believe represent fundamental properties of spatial systems. In fact, we suggest that these dimensions can be applied to more general CSCW systems which are "situated" in the physical every-day world, although this is beyond the scope of this paper.

Figure 1 shows how various meeting technologies can be of classified according to these two orthogonal dimensions. Let us consider the various examples in this picture in more detail. The users of a telephone conference essentially remain in the physical world where supplementary material is all a direct rendering of remote physical events. Thus, telephone conferencing is fundamentally both local and physical. Similarly, in a traditional small screen video conference, users remain in their local physical world and view remote video footage of physical events. The use of a small screen minimises any sense of immersion in the remote scene and thus assigns a dominant role to the local environment. Video conferencing enhanced with shared data (e.g. shared editors) [28] introduces a certain amount of synthetic information and hence involves greater artificiality than minimal video-conferencing. Hydra [19] introduces a consistent multi-party space in which gaze direction and the ordering of participants is meaningful (e.g. X will be to the left of Y for every participant). The sharing of a conference space weakens the role of the local space. However, all the information displayed is still a direct representation of the physical world. The use of large screens in video conferencing between two sites (e.g. [27]) may give users a stronger sense of involvement in the remote scene, implying a degree of transportation, but still retains its physical nature. The MAJIC system, especially with background substitution, encourages its participants to enter a new hybrid space, leaving their local environment, but still being represented by their physical body. However, the participants take proportionally less of their immediate physical context with them. In particular, the use of synthetic backdrops moves MAJIC away from the strictly physical end of the artificiality dimension and introduces a degree of synthesis. The use of larger projected displays also strengthens the role of the remote scene when compared to the small displays used in Hydra,

Transportation and artificiality The dimension of transportation concerns the extent to which a shared space introduces new information into its users' local spaces versus the extent to which it allows them to enter remote spaces; in other words it characterises the essential difference between the concepts of local and remote. One extreme of this dimension involves being wholly involved with (and thinking in terms) of a user's immediate physical environment. This would be the case in a physical face-to-face meeting. At the other extreme is total involvement with and immersion in a remote environment of some kind. Immersive virtual reality and tele-presence applications are exemplars of this extreme.

At intermediate degrees of transportation we find split levels of involvement, attending to aspects of both the immediate physical environment and the remote environment. As one moves towards the transportationless extreme, the remote environment becomes less significant and impinges less on the immediate context. As one moves towards the totally transported extreme, the immediate environment becomes less significant; it may seem that less of the physical environment is being drawn into the remote environment.

In tele-presence systems, users substitute (as much as is possible) their immediate surroundings for the representation of a remote but physically real location. In contrast, immersive collaborative virtual environments, attempt to cut their users off from their physical surroundings and, instead, immerse them in a wholly synthetic computer-generated environment. However, the introduction of facial expressions in CVEs (through video recognition and facial animation techniques) weakens the synthetic nature of VR to a degree.

The dimension of artificiality spans the extremes from wholly synthetic environments to wholly physical environments, i.e. between the electronically mediated delivery of a physical place, firmly based in everyday reality, and the total synthesis of an environment independent of all external reality from nothing but bits in a computer. Video conferencing is typical of the physical extreme (its information is all drawn from the real world), while abstract data visualisation or computer art exemplifies the synthetic extreme.

The nature of the interface technology used may have a considerable effect on transportation. Projection based interfaces to virtual environments, whilst retaining their synthetic nature, open the user to greater local influence 3

than do immersive interfaces, as their view is not isolated from the immediate physical context to the same extent. Shared projected interfaces such as CAVEs and VR domes, while providing almost complete immersion, may be less transporting than immersive interfaces because a number of physically co-located participants can share a single CAVE. Thus the group (which reflects the physical locality) are transported together into the virtual world. Desktop virtual reality interfaces typically expose the user to still-greater interference from local stimuli and distractions and thereby situate them more fully in their local surroundings. Indeed, early trials with the MASSIVE system have identified the so-called degree

synthetic (generated from computer data)

of presence problem, where users who are embodied in the virtual world temporarily step out of their bodies due to some local distraction ,causing confusion for other users who are trying to interact with them in the virtual world [9]. Augmented reality systems (e.g. the Head-up Displays developed for pilots) supplement the users immediate physical surroundings with additional synthetic information (e.g. annotations and projections), but the immediate surroundings remain the first consideration. They are essentially local in terms of transportation and relatively synthetic in terms of artificiality.

Augmented Reality

Desktop CVEs

Projected CVEs

Immersive CVEs

CVEs with faces hybrid

Dimension of Artificiality physical (generated from the real world)

Video conf with shared data

MAJIC

Phone/video conference (small screen) Portland Physical Hydra Experience meeting local (remain in the physical world)

partial (leave some things but take others)

Telepresence

remote (leave your body behind)

Dimension of Transportation

Telephone and video conferencing Place (containment only)

"Total" mediaspace hypertext/WWW

Simple graph space (adds topology and limited movement)

Hydra

Constrained graph space (enhanced topology)

Large screen video conf (where made spatially consistent) MAJIC CVEs Telepresence Shared spatial frame (i.e. Cartesian space with movement)

Dimension of Spatiality

Figure 1: A classification of shared spaces according to the dimensions of transportation, artificiality and spatiality An interesting issue raised by this classification is the role of different underlying technologies in locating systems along these dimensions. Choosing to implement a shared space using video or using interactive graphics will tend to locate it more towards the physical or synthetic ends of the artificiality dimension respectively.

The choice of display technology (small screen, large screen, projected or immersive) locates the resulting system along the transportation dimension. Thus, to generalise, the medium affects artificiality and the display affects transportation.

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Spatiality Another dimension which may be used to characterise CSCW systems is their degree of spatiality. This dimension characterises systems according to their level of support for fundamental spatial properties such as containment, topology, distance, orientation and movement (see figure 1). Its extremes are characterised by the notion of place, a basic containing context for participants; and space, a context which provides a consistent, navigable and shared spatial frame of reference (e.g. Cartesian space). Unlike the previous two dimensions which might be applied to CSCW systems in general, spatiality (obviously) applies specifically to the kinds of system discussed in this paper.

preserves the relationship "is-looking-at", but distorts the angles and inferred positions in any postulated shared Cartesian space. Thus, Hydra's space is structured as a graph but with additional constraints which introduce a limited set of spatially-related characteristics such as who is looking at whom.

The management and control view of a mediaspace may include explicit notions of place, e.g. offices (or rather the camera views of those offices). Additionally, these places may be organised into a linked network. That network is itself a place (the mediaspace in its entirety) but is also a graph-space. I.e. within the mediaspace as a whole, participants can move in well-defined ways between different sub-places. The set of sub-places and the ways in which they are related define the total media space. This type of system therefore moves away from the placeful extreme to include some basic spatiality in the form of a graph-like topology and limited movement.

In summary, shared space systems can be characterised according to their degree of spatiality. The least spatial systems, places, support the basic spatial property of containment. The subsequent introduction of other spatial properties such as topology, movement and a shared spatial frame of reference results in increased spatiality.

Large-screen video-conferencing systems such as the Portland Experience and the MAJIC three-way conference have a shared space which is very closely related to the real world but does not exist in its entirety in any one physical location. For example, MAJIC creates a new meeting space which has mutually consistent extents, positions, etc. but which is composed from three disjoint portions of physical space. Its effect is to take the three We begin with the basic notion of shared space. 120 degree segments of space (each of the offices involved in the meeting) and join them together into a Logically, the shared space in which a cooperative new physical space. Thus, the conference space is spatial activity occurs can be defined to be those aspects of the in the same way that a normal meeting space is, and all system which are independent of any single participant or participants can agree about the nature and arrangement of group of participants and which are agreed on by the the conference space. This system therefore introduces the participants. This is expanded and illustrated in the fundamental notion of a shared spatial frame of reference; following observations of current systems. a commonly defined Cartesian co-ordinate system through which relative positions and orientations can be In minimal video conferencing (single camera per group measured. However, there is still only limited ability to of participants, no shared electronic data space), the space move about within this spatial frame (i.e. one cannot which is independent of each participant, and on which all step into another participants' region of the shared space). participants can agree, is just the set of participants and their allocation to cameras. There is no higher-level Another class of fully spatial system is a 3-D relationship between the groups of participants. The use collaborative virtual environment, in which all of a single camera per-participant prevents participants participants observe the same (virtual) 3-D space and see from tailoring their visual communication actions objects with the same extents and in the same relative towards any subset of recipients. This type of system is positions and orientations. Participants differ only in characteristic of the placeful extreme on the spatiality their personal viewpoint, and viewpoints are represented scale. This is because there is place - the conference - in to other participants (as in the everyday world) by bodies; which the participants agree they are, in some sense, from these each participant can infer what the other present. However there is no internal structure to this participants are seeing. A key aspect of CVEs is that they place, no dimensions or controls, and therefore little support general movement within a shared spatial frame. spatiality, other than basic containment.

Towards new kinds of shared space Other than as an observation on current spatial approaches to CSCW, there are two primary uses for such as classification. First, it informs us about the likely effects of making different technological choices when building shared space systems (e.g., we can reason about the effects of using different media and display technologies). Second, and perhaps more importantly, it suggests technology gaps where new kinds of application might be created. Comparing systems through continuous dimensions encourages us to move away from making discrete choices between technological extremes and, instead, leads us think of hybrid approaches which unify different technologies. This brings us to the second part of our paper, a new kind of shared space application which occupies different points along our various dimensions and which represents an integration of several current approaches into a kind of system that we might generally refer to as a mixed reality.

Hydra is more spatial again. In Hydra, the space is the conference within which are the participants. Unlike a minimal video conference, the participants in a Hydra conference are in well-defined relationships to one another, and all participants agree about these relationships. The participants are arranged in a ring with exactly one neighbour on each side and all participants agree about who is neighbour to whom. However the participants cannot be given consistent spatial locations because each participant "stretches" their part of the ring so that they can look at all the other participants' local representatives (camera-screen systems) simultaneously. This stretching or warping of the conference space

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able to interact with those entering its physical space and vice versa.

MIXED REALITY - THE INTERNET FOYER

In this section we will introduce an example of a mixed reality, a shared space which, from different users' perspectives, occupies several locations along our dimensions of transportation and artificiality and which provides a high degree of spatiality. This example, called the Internet Foyer, will combine both local and remote and synthetic and physical characteristics into a single system on an equal footing. We begin with the goal of the Internet Foyer.

The functionality of the Internet Foyer

The overall concept of the Internet Foyer is summarised by figure 2. On the left of the picture we see visitors in a traditional physical foyer. Projected onto the wall of this physical foyer for its inhabitants to see is a graphical visualisation of the virtual foyer. On the right of the picture we see the virtual foyer, a 3-D graphical visualisation of an organisation's home pages whose electronic visitors are mutually embodied (i.e. visible to one another) and are able to communicate with one another through open audio channels. A video window in the virtual foyer affords its occupants a corresponding view back into the real foyer and an open audio channel allows communication between the two spaces.

The goal of the Internet Foyer

Foyers are important areas of physical buildings for a variety of reasons. First, they present the public face of a building and the organisation(s) which it houses. The significance of this function alone should not be underestimated; large sums of money are spent on making foyers interesting and impressive places. Second, foyers provide a context for locating useful information for visitors such as maps, directories and displays. Third, from a cooperative point of view, they may be home to various people whose job it is to help these visitors (e.g. receptionists). Fourth, they enhance security by providing a single point of entry into the organisation within which incoming and outgoing people are made publicly visible and hence accountable. Indeed, foyers may often contain security staff and areas where visitors sign in. Fifth, they provide public meeting places, either for arranged rendezvous or for chance encounters. Some larger foyers contain shops, cafŽs and other facilities which encourage this kind of social function.

There are three ways to experience the Internet Foyer: as a visitor to the physical foyer, as the user of a collaborative virtual environment and as the user of a traditional WWW browser. The following paragraphs summarise the functionality of the Internet Foyer as seen by each of these types of user. As a visitor to the physical foyer: such users enter a normal physical space. Projected onto a wall of that space is the graphical representation of the virtual foyer. This representation shows a number of linked WWW pages drawn as a 3-D network structure. It also shows the presence of virtual reality users in the virtual foyer via graphical user embodiments which move around this visualisation. These graphical embodiments include live video textured faces in order to convey facial expression. In addition, the visualisation shows graphical representations of traditional WWW browser users who happen to be wandering across the pages depicted in the visualisation. Animated movements show the progress of these users as they flit from page to page. Finally, an open audio link allows communication with the virtual reality users in the virtual foyer.

Turning away from physical space and towards virtual space for a moment, it is clear that many organisations are making increasing use of computer networks and many have established a public network presence through services such as the World Wide Web. Thus, in parallel with the physical manifestation of buildings, organisations are increasingly acquiring an electronic manifestation through computer networks. In such cases, the public "home" pages of an organisation on the WWW could be considered to be a kind of foyer: a public entry point into the organisation's network manifestation. There is certainly evidence that organisations are investing considerable effort into turning their WWW pages into interesting and impressive places.

As the user of a collaborative virtual environment: CVE users see the same basic visualisation as those in the physical foyer, However, they are able to freely navigate around the visualisation, homing in on specific details or backing off in order to obtain a perspective view. They are also able to select objects in the visualisation (both representations of WWW pages and of other users). At present, selecting another object launches the Mosaic WWW browser to display its contents. A real-time video window which is texture mapped onto a wall of the virtual foyer allows CVE users to look out into the physical foyer and to see its occupants looking back at them. Finally, an open audio link supports communication with other CVE users and with those in the physical foyer.

However, when considered as foyers, WWW pages leave much to be desired. The people who pass through them are not generally visible to one another or to other observers (a major criticism of current WWW technology in general). Thus, security may be compromised and there are no opportunities for rendezvous and social encounters. There are therefore two main goals to the Internet Foyer: 1.

2.

To construct a virtual foyer based on a populated visualisation of an organisation's WWW space which might come closer to the functionality of a real foyer. On its own, this virtual foyer would represent an application of CVE technology.

As the user of a traditional WWW browser: These users see the Internet foyer as a series of WWW pages. On entering the foyer they are asked to register themselves using a simple form. Beyond this, additional pages provide information about current and recent visitors, displayed as simple textual lists and may display captured images from both the real and virtual foyers.

To merge this virtual foyer with the real foyer to provide an integrated shared space which spans both the physical and virtual worlds. Thus, visitors entering an organisation's WWW space would be 6

WWW visualisation Embodied CVE user

real-world users

Physical Foyer Representation of a 2-D (e.g. Mosaic) user

Virtual Foyer

Figure 2: The Functionality of the Internet Foyer

world database are maintained in a consistent state as a result of the transmission of updates.

Figures 3, 4 and 5 present images of the Internet Foyer as it appears to different users. Figure 3 shows an overview of the Internet Foyer as it appears to a CVE user. The image shows a visualisation of several interlinked WWW pages (green spheres connected by blue arrows), the presence of another CVE user (yellow body with live video face), a distant video window into the physical foyer and also the presence of several Mosaic users. Figure 4 shows a view from the same user when they have homed in on a specific part of the WWW visualisation. This image shows how the presence of the Mosaic users is represented in more detail. Selecting one of the spheres or one of these user representations would result in the Mosaic browser being launched in order to display its contents (a WWW page). Finally, figure 5 shows how the Internet Foyer appears to visitors in the physical foyer. It should be noted that, at the present time, the Internet Foyer has only been configured in our local laboratory (we plan to install it in a more realistic situation - i.e. a real foyer - over the next few months).

Constructing the visualisation The visualisation of the connected WWW pages has been produced by an application called FDP-Grapher (which has been implemented in DIVE). FDP-Grapher dynamically constructs 3-D visualisations of network structures using the Force Directed Placement (FDP) technique. This technique is based on a physical simulation model which treats the nodes of the network as masses and the arcs as springs. The whole structure is placed in a random initial configuration and a series of iterations are performed in which the physical effects of the springs on the masses are simulated. This continues until the visualisation settles in a stable state. The resulting visualisations typically group strongly interlinked nodes into spatial clusters.

In the Internet Foyer, FDP-Grapher has been connected to a simple WWW robot which explores a region of the WWW as defined by an initial URL and a link adjacency distance. Thus, the visualisation is capable of charting arbitrary regions of the WWW (of up to a few hundred nodes before scaleability problems set in with the FDP implementation). The FDP algorithm has also been adjusted to treat single outlying pages as lighter nodes and strongly linked pages as heavier ones in order to produce a more legible final visualisation.

The implementation of the Internet Foyer

The implementation of the Internet Foyer relies on the integration of several existing technologies. The following paragraphs highlight the key techniques used. The Collaborative Virtual Environment The virtual foyer component of the Internet Foyer has been implemented using the DIVE Collaborative Virtual Environment platform (version 3). DIVE is a general purpose toolkit which has been developed by the Swedish Institute of Computer Science [6]. DIVE allows multiple users to enter a 3-D graphical environment and to interact with one another. DIVE has also provided the default embodiments for the CVE users. DIVE is based on a distributed database model where local copies of a virtual

Video and audio support The Internet foyer includes the use of texture mapped video streams, both to provide CVE participants with a view of the remote physical foyer and also to introduce facial expressions onto their embodiments. This involves a real-time video stream being attached to a surface (currently a single polygon) in the DIVE environment and being constantly re-textured as new frames arrive. The video data is transmitted over a multi-cast protocol and in 7

the interpretation of the notion of shared space. The first contribution of the paper has been to review current spatial approaches to CSCW (i.e. mediaspaces, spatial video conferencing, collaborative virtual environments and telepresence applications) with a view to understanding the fundamental differences between them. This review classified a wide range of current approaches along the three dimensions of transportation (the degree to which a user is transported into some new space); artificiality (the degree to which the shared space is based on the real world or is synthesised) and spatiality (the degree to which the shared space exhibits key spatial properties such as containment, topology, movement and a shared frame of reference).

its current uncompressed form, this approach is capable of supporting a couple of video streams plus audio channels and virtual world updates on a standard Ethernet and achieves a video frame rate in excess of ten frames per second. Audio data is currently handled by dedicated audio server processes which run over UDP. Tracking WWW browsers The final software component of the Internet Foyer is called FollowWWW. This is a general package for tracking the presence of WWW browsers as they pass through a server. These users are then represented by simple graphical embodiments in DIVE which are animated to reflect movement between different WWW pages in the visualisation. FollowWWW can use either live data or WWW server log files as its input.

This classification has also hilited the role of different underlying technologies, particularly the way in which the use of video or interactive graphics to generate the world content affects the degree of artificiality and the way in which the use of different display technologies affects the transportation dimension.

Classifying the Internet Foyer

So where does the Internet Foyer fit into our classification scheme? First, it clearly combines aspects of telepresence (looking into the remote physical foyer); mediaspaces (support for peripheral awareness and chance encounters); collaborative virtual environments (shared 3D data visualisations) and of spatial video conferencing (support for video faces attached to graphical bodies within a common spatial frame of reference). With reference to our various dimensions, the Internet Foyer combines aspects of both the physical and synthetic worlds into a single system, placing it along the midpoint of the artificiality dimension. As the Internet Foyer can be accessed either though a physical foyer or remotely using CVE technology, it might be located at either of the local or remote points of the scale of transportation. This raises the issue of heterogeneity. A key aspect of the Internet Foyer is that it provides different kinds of access to different users. Thus, visitors to the real foyer experience a reasonably familiar local environment enhanced through projected graphics, whereas virtual users experience a new remote one. This, in stark contrast to the applications reviewed earlier which provided homogeneous styles of access. Thus, a primary function of the Internet Foyer is to demonstrate how different approaches can be blended into a coherent whole.

However, recognising the distinctions between current approaches is not by itself sufficient to carry development of these technologies forward. Consequently, the classification of current systems along continuous dimensions has led us to think about hybrid approaches which combine different kinds of shared space into a single system. We have presented an example of a so called mixed reality. Our example, called the Internet Foyer, involves the creation of a shared space which spans physical and synthetic, and local and remote worlds to equal degrees. The goal of the Internet Foyer has been to create a single entry point into an organisation's space which can be shared by both its physical and virtual visitors. Thus, the electronic manifestation of the organisation is made visible and linked to the existing physical one. The implementation of the Internet Foyer relies on the integration of video and graphical technologies, currently achieved by texture-mapping realtime video streams onto surfaces in a 3-D virtual world. It also requires the use of public or shared display technology (in this case a projection system). What other mixed reality applications might be possible? The obvious candidates are those which involve knowledge of events in the real world combined with distributed access to electronic data. For example:

In terms of its spatiality, the Internet Foyer is strongly spatial. It includes aspects of containment, topology, navigation and provides a shared spatial frame of reference, both within the virtual foyer and across the boundary between the virtual and physical foyers. However, there are some limitations. At present, visitors to the physical foyer cannot navigate their own viewpoints within the virtual foyer; they have a static view of the visualisation. Although it would be relatively simple to provide an interface for a single user to navigate, extending this to multi-user support is more difficult. This issue really applies to all forms of shared or public display; how can a group of people easily negotiate control over a single display? SUMMARY

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Doctors whose diagnoses might involve the ability to see a real live patient (e.g. to sit in on a remote clinical session) and also to visualise 3-D scan data captured by various medical imaging techniques.

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Construction engineers who need to discuss engineering plans and data within the context of an emerging physical building.

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Environmental planners who wish to discuss geographical data captured through environmental remote sensing techniques in the context of some real-world environmental development.

The extent to which such applications might be located along the different dimensions of transportation, artificiality and spatiality will no doubt depend upon the nature of the data being discussed, whether remote

This paper has been concerned with the spatial approach to CSCW, an approach which seems to have gathered considerable interest over recent years. The aim of the paper has been to contribute to the growing debate about 8

collaboration is required and other factors such as available technologies. However, it seems unlikely that any of them should fall at the extremes of any of these dimensions, or could be fully supported by any of the current spatial approaches. In conclusion, the most fruitful direction for CSCW research into shared spaces might be to consider techniques for synthesising the physical and synthetic environments into varying forms of mixed reality.

13. Ishii, H. and Kobayishi, M., Integration of InterPersonal Space and Shared Workspace: ClearBoard Design and Experiments, Proc. CSCW'92, Toronto, Canada, November, 1992, ACM Press, PP 33-42. 14. Kuzuoka, H., Ishimoda, G. and Nishimura, T., Can the GestureCam be a surrogate?, Proc. ECSCW'95, Stockholm, Sweden, September 1995, Kluwer. 15. Ohya, J., Kitamura, Y., Takemura, H., Kishino, F., Terashima, N., Real-time Reproduction of 3D Human Images in Virtual Space Teleconferencing, in Proc.VRAIS'93, IEEE, Seattle Washington REFERENCES September, 1993, pp. 408-414. 1. Benford, S., Bowers, J., FahlŽn, L. E., Mariani, J. 16. QuŽau, P., Real Time Facial Analysis and Image and Rodden, T., Supporting Co-operative Work in Rendering for Televirtuality Applications, in Notes Virtual Environments, The Computer Journal, Vol from Virtual Reality Oslo '94 Ñ Networks and 37, Number 8, Oxford University Press, 1994. Applications, eds. Loeffler, Carl E and S¿by, 2. Bly, S. A., Harrison, S. R., Irwin, S., Media Morten and ¯degŒrd, Ola, August 1994. Spaces: Video, Audio, and Computing, 17. Root, R., W., Design of a multi-media vehicle for Communications of the ACM, No.1 Vol.36, social browsing, Proc CSCW'88, Portland, Oregan, January 1993, pp. 28-47. 1988, ACM Press, pp 25-38. 3. Brand, S., The Medialab Ñ Inventing the future at 18. Sacks, H., Schegloff, E. and Jefferson, G. A MIT, Viking Penguin, 1987, pp. 91-93. Simplest Systematics for the Organisation of Turn4. Cook,S., Birch,G., Murphy, A., and Woolsey, J., Taking in Conversation, Language, Vol. 50, pp. Modelling Groupware in the Electronic Office, in 696-735, 1974. Computer-supported Cooperative Work and 19. Sellen, S. and Buxton, B., Using Spatial Cues to Groupware, Saul Greenberg (ed), Harcourt Brace Improve Videoconferencing, Proc. CHI'92, May 3Jovanovich, 1991, ISBN 0-12-299220-2. 9, 1992, pp 651-652, ACM Press. 5. Cruz-Neira, C., Sandin, D. J., DeFant, T. A., 20. Shu, L., and Flowers, W., Groupware Experiences Kenyon, R. V. and Hart, J. C., The Cave - Audio in Three-Dimensional Computer-Aided Design, in Visual Experience Autoiac Virtual Environment, Proc. CSCW'92, ACM Press, 1992. CACM, 1992, 35 (6), pp 65-72, 1992. 21. Stone, R. J., Advanced Human-System Interfaces 6. FahlŽn, L. E., Brown C. G., Stahl, O., Carlsson, for Telerobotics Using Virtual Reality and C., A Space Based Model for User Interaction in Telepresence Technologies, Proc. Fifth International Shared Synthetic Environments, in Conference on Advanced Robotics in Unstructured Proc.InterCHI'93, Amsterdam, 1993, ACM Press. Environments (ICAR'91), June 1991. 7. Gaver W., The Affordances of Media Spaces for 22. Suchman, L., Do categories have politics? The Collaboration, In Proc. CSCWÕ92, Toronto, language/action perspective reconsidered, Computer November 1992, ACM Press. Supported Cooperative Work, 2 (3), 177-190. 8. Gaver, W., Moran, T., MacLean, A.,Lovstrand, L., 23. Suzuki, G., Interspace: Toward Networked Virtual Dourish,P., Carter, K. and Buxton W., Realising a Reality of Cyberspace, Proc. Imagina'95, MonteVideo Environment: EuroPARC's RAVE System, Carlo, February, 1995, INA. In Proc. CHI '92 Human Factors in Computing 24. Takemura, H., and Kishino, F., Cooperative Work Systems, Monterey, Ca., USA. Environment Using Virtual Workspace, In Proc. 9. Greenhalgh, C. and Benford, S., MASSIVE: A CSCW'92, Toronto, Nov 1992, ACM Press. Virtual Reality System for Tele-conferencing, ACM 25. Winnograd, T., Categories, disciplines and social Transactions on Computer Human Interaction coordination, Computer Supported Cooperative (TOCHI), ACM Press (in press). Work, 2 (3), 191-197, Kluwer, 1994. 10. Heath, C. and Luff, P., Collaborative Activity and 26. Zyda, M.J., Pratt, D.R., Falby, J.S., Lombardo, C. Technological Design: Task Coordination in and Kelleher, K.M., The Software Required for London Underground Control Rooms. In L. Computer Generation of Virtual Environments, Bannon, M. Robinson and K. Schmidt Presence, 2 (2), Spring, 1993, pp 130-140. (eds),Proceedings of ECSCW91, Sept 25-27, Dordrecht: Kluwer, 1991. 27. Olson, M. H. and Bly, S. A., The Portland Experience: a report on a distributed research group, 11. Hughes, J.A., Randall, D., and Shapiro, D., in Computer-supported Cooperative Work and Faltering from Ethnography to Design, in Proc. Groupware, Ed. Saul Greenberg, Academic Press. CSCW'92, ACM Press, Toronto, Canada. 28. Sarin, S., & Greif, I., Shared-data conferencing, 12. Ichikawa, Y., Okada, K., Jeong, G., Tanaka, S. and (1985), Computer-based real-time conferencing Matushita, Y., MAJIC Videoeonferencing System: systems, IEEE Computer, 18(10), pp. 33-45. Experiments, Evaluation and Improvement, Proc ECSCW'95, Stockholm, Sweden, 1995, Kluwer.

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COVER PAGE CSCW'96 SUBMISSION

SHARED SPACES: TRANSPORTATION, ARTIFICIALITY, AND SPATIALITY Steve Benford, Chris Brown, Gail Reynard and Chris Greenhalgh

Department of Computer Science The University of Nottingham Nottingham NG7 2RD, UK. E-mail: {sdb, ccb, gtr, cmg}@cs.nott.ac.uk Tel: +44 115 9514203 Fax: +44 115 9514254

CATEGORY OF SUBMISSION: PAPER PRIMARY CONTACT PERSON: STEVE BENFORD

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