IN Proceedings of the First International Symposium on Mixed Reality (ISMR ’99). Mixed Reality – Merging Real and Virtual Worlds, pp. 261-284. Berlin: Springer Verlag. Collaborative Mixed Reality Mark Billinghurst, Hirokazu Kato Human Interface Technology Laboratory University of Washington Box 352-142 Seattle, WA 98195, USA {grof, kato}@hitl.washington.edu Abstract Virtual Reality (VR) appears a natural medium for computer supported collaborative work (CSCW). However immersive Virtual Reality separates the user from the real world and their traditional tools. An alternative approach is through Mixed Reality (MR), the overlaying of virtual objects on the real world. This allows users to see each other and the real world at the same time as the virtual images, facilitating a high bandwidth of communication between users and intuitive manipulation of the virtual information. We review MR techniques for developing CSCW interfaces and describe lessons learned from developing a variety of collaborative Mixed Reality interfaces. Our recent work involves the use of computer vision techniques for accurate MR registration. We describe this and identify areas for future research. Keywords: Mixed Reality, Augmented Reality, Virtual Reality, Computer Supported Collaborative Work 1 Introduction Computers are increasingly used to enhance collaboration between people. As collaborative tools become more common the Human-Computer Interface is giving way to a Human-Human Interface mediated by computers. This emphasis on collaboration adds new technical challenges to the design of Human Computer Interfaces. There are also many social factors that must be addressed before collaborative tools will become common in the workplace. These problems are compounded for attempts to support three-dimensional Computer Supported Collaborative Work (CSCW). Although the use of spatial cues and three-dimensional object manipulation are common in face to face communication, tools for three-dimensional CSCW are still rare. However new interface metaphors may overcome this limtation. In this paper we describe how Mixed Reality techniques can be used to enhance remote and face to face collaboration, particularly 3D CSCW. Mixed Reality (MR) environments are defined by Milgram as those in which real world and virtual world objects are presented together on a single display [27]. Single user Mixed Reality interfaces have been developed for computer aided instruction [9], manufacturing [7] and medical visualization [2]. These applications have shown that Mixed Reality interfaces can enable a person to interact with the real world in ways never before possible. For example, the work of Bajura et. al. overlays virtual ultrasound images onto a patients body, allowing doctors to have “X-Ray” vision while performing a needle biopsy task [2]. Although Mixed Reality techniques have proven valuable in single user applications, there has been less research on collaborative applications. We believe that Mixed Reality is ideal for collaborative interfaces because it addresses two major issues in CSCW: seamlessness and enhancing reality. In the next section we describe these issues in depth. We then review approaches for 3D CSCW and describe examples from our work and others of how Mixed Reality can be used to support local and remote collaboration. Finally we conclude with a description of new computer vision techniques for collaborative Mixed Reality interfaces. 2 Motivation: Why Collaborative Mixed Reality 2.1 Seamless Computer Supported Collaborative Work When people talk to one another in a face-to-face conversation while collaborating on a real world task there is a dynamic and easy interchange of focus between the shared workspace and the speakers’ interpersonal space. The shared workspace is the common task area between collaborators, while the