We present Avocado, our object-oriented framework for the development of distributed, interactive VE applications. Data distribution is achieved by transparent replication of a shared scene graph among the participating processes of a distributed application. A sophisticated group communication system is used to guarantee state consistency even in the presence of late joining and leaving processes. We also describe how the familiar dataflow graph found in modern stand-alone 3D-application toolkits extends nicely to the distributed case. 1.

Virtual reality technology has begun to emerge from research labs. People are beginning to make use of it in mainstream work environments. However, there is still a lack of well-designed virtual reality application development environments. This thesis describes VR Juggler, a virtual platform for the creation and execution of immersive applications, which provides a virtual reality system-independent operating environment. The thesis focuses on the approach taken to specify, design, and implement VR Juggler and the benefits derived from this approach.

Our starting point for developing the Studierstube system was the belief that augmented reality, the less obtrusive cousin of virtual reality, has a better chance of becoming a viable user interface for applications requiring manipulation of complex three-dimensiona information as a daily routine. In essence, we are searching for a 3-D user interface metaphor as powerful as the desktop metaphor for 2-D. At the heart of the Studierstube system, collaborative augmented reality is used to embed computer-generated images into the real work environment In the #rst part of this paper, we review the user interface of the initial Studierstube system, in particular the implementation of collaborative augmented reality , and the Personal Interaction Panel, a two-handed interface for interaction with the system. In the second part, an extended Studierstube system based on a heterogeneous distributed architecture is presented. This system allows the user to combine multiple approaches--- augmented reality, projection displays, and ubiquitous computing---to the interface as needed. The environment is controlled by the Personal Interaction Panel, a twohanded, pen-and-pad interface that has versatile uses for interacting with the virtual environment. Studierstube also borrows elements from the desktop, such as multitasking and multi-windowing. The resulting software architecture is a user interface management system for complex augmented reality applications. The presentation is complemented by selected application examples 1

This article proposes and tests a two-component model for describing and programming the finegrained aspects of non-WIMP interaction. The model combines a data-flow or constraint-like component for the continuous relationships with an event-based component for discrete interactions, which can enable or disable individual continuous relationships. Its key ingredients are the separation of non-WIMP interaction into two components and the framework it provides for communication between the two

This article describes OpenTracker, an open software architecture that provides a framework for the di#erent tasks involved in tracking input devices and processing multimodal input data in virtual environments and augmented reality application. The OpenTracker framework eases the development and maintenance of hardware setups in a more flexible manner than what is typically o#ered by virtual reality development packages. This goal is achieved by using an object-oriented design based on XML, taking full advantage of this new technology by allowing to use standard XML tools for development, configuration and documentation. The OpenTracker engine is based on a data flow concept for multimodal events. A multi-threaded execution model takes care of tunable performance. Transparent network access allows easy development of decoupled simulation models. Finally, the application developer's interface features both a time-based and an event based model, that can be used simultaneously, to serve a large range of applications. OpenTracker is a first attempt towards a "write once, input anywhere" approach to virtual reality application development. To support these claims, integration into an existing augmented reality system is demonstrated. We also show how a prototype tracking equipment for mobile augmented reality can be assembled from Preprint submitted to Elsevier Science 12 April 2001 consumer input devices with the aid of OpenTracker. Once development is su#- ciently mature, it is planned to make Open-Tracker available to the public under an open source software license. Key words: Tracking, Mobile Augmented Reality, Virtual Reality, XML 1

As virtual environment (VE) technology becomes accessible to and affordable for an everwidening audience of users, there will be an increase in demand for VE applications. Tools that assist and facilitate the development of these applications, therefore, will also be in demand. To support our efforts in quickly designing and implementing virtual environment applications, we have developed the Simple Virtual Environment (SVE) library. In this article we describe the characteristics of the library which support the development of both simple and complex VE applications. Simple applications are created by novice programers or for rapid prototyping. More complex applications incorporate new user input and output devices, and new techniques for user interaction, rendering, or animation. The SVE library provides more comprehensive support for developing new VE applications, and better supports the various device configurations of VE applications than current systems for 3D graphical applicat...

Distributed Open Inventor is an extension to the popular Open Inventor toolkit for interactive 3D graphics. The toolkit is extended with the concept of a distributed shared scene graph, similar to distributed shared memory. From the application programmer's perspective, multiple workstations share a common scene graph. The proposed system introduces a convenient mechanism for writing distributed graphical applications based on a popular tool in an almost transparent manner. Local variations in the scene graph allow for a wide range of possible applications, and local low latency interaction mechanisms called input streams together with a sophisticated networking architecture enable high performance while saving the programmer from network peculiarities. Keywords Distributed graphics, concurrent programming, scene graph, distributed virtual environment, computer supported cooperative work, virtual reality 1.

This paper describes OpenTracker, an open software architecture that provides a generic solution to the different tasks involved in tracking input devices and processing tracking data for virtual environments. It combines a highly modular design with a configuration syntax based on XML, thus taking full advantage of this new technology. OpenTracker is a first attempt towards a "write once, track anywhere" approach to virtual reality application development. To support these claims, integration into an existing augmented reality system is demonstrated. Once development is sufficiently mature, it is planned to make OpenTracker available to the public under an open source software license. 1. Introduction Tracking is an indispensable requirement for all kinds of virtual reality (VR) and augmented reality (AR) systems. While the quality of tracking, in particular the need for high performance and fidelity have led to a large body of past and current research, little attention is typicall...

We present a strategy for rendering in distributed virtual environments. A geometry database is maintained by a server, while users invoke individual clients to interact with the environment. Instead of downloading a complete copy of the geometry data, the data is distributed on demand, thus gaining significant savings in network bandwidth. Our strategy combines several techniques, including levels of detail, progressive refinement and graceful degradation to deliver the data "just in time" over the network to the rendering process. The method allows operate on a tight resource budget, which important if attempting to use low cost systems for virtual reality applications.

The Environment Manager (EM) is a high-level tool for constructing both single user and multi-user virtual environments. A script file is used to initialize and run virtual worlds. Independent applications can share information and cooperate with each other across the Internet. EM reduces the effort required to produce a networked virtual world by providing highlevel support for application replication, network configuration, communication management and concurrency control. This paper describes the architecture and implementation of EM. 1 Introduction With many single-user Virtual Reality(VR) applications being successfully implemented [3, 12, 13, 10, 17], Networked Virtual Reality is now becoming a hot topic. Networked Virtual Reality refers to virtual environments where multiple users connected by a network can share information with each other. The production of good VR worlds, whether single user or networked, requires a considerable amount of design and programming time. Expert...