Anton L. Fuhrmann

Occlusion in Collaborative Augmented Environments

Abstract Augmented environments superimpose computer enhancements on the real world. Such augmented environments are well suited for collaboration of multiple users. To improve the quality and consistency of the augmentation the occlusion of real objects by computer-generated objects and vice versa has to be implemented. We present methods how this can be done for a tracked users body and other real objects and how irritating artifacts due to misalignments can be reduced. Our method is based on simulating the occlusion of virtual objects by a representation of the user modeled as kinematic chains of articulated solids. Smoothing the border between virtual world and occluding real reduces registration and modeling errors of this model. Finally, an implementation in our augmented environment and the resulting improvements are presented.

Bridging multiple user interface dimensions with augmented reality

Studierstube is an experimental user interface system which uses collaborative augmented reality to incorporate true 3D interaction into a productivity environment. This concept is extended to bridge multiple user interface dimensions by including multiple users, multiple host platforms, multiple display types, multiple concurrent applications and a multi-context (i.e. 3D document) interface into a heterogeneous distributed environment. With this architecture, we can explore the user interface design space between pure augmented reality and the popular ubiquitous computing paradigm. We report on our design philosophy, which is centered around the notion of contexts and locales, as well as the underlying software and hardware architecture. Contexts encapsulate a live application together with 3D (visual) and other data, while locales are used to organize geometric reference systems. By separating geometric relationships (locales) from semantic relationships (contexts), we achieve a great amount of flexibility in the configuration of displays. To illustrate our claims, we present several applications, including a cinematographic design tool which showcases many features of our system.

“Studierstube”: An environment for collaboration in augmented reality

We propose an architecture for multi-user augmented reality with applications in visualisation, presentation and education, which we call “Studierstube”. Our system presents three-dimensional stereoscopic graphics simultaneously to a group of users wearing light weight see-through head mounted displays. The displays do not affect natural communication and interaction, making working together very effective. Users see the same spatially aligned model, but can independently control their viewpoint and different layers of the data to be displayed. The setup serves computer supported cooperative work and enhances cooperation of visualisation experts. This paper presents the client-server software architecture underlying this system and details that must be addressed to create a high-quality augmented reality setup.

Real-time techniques for 3D flow visualization

Visualization of three-dimensional steady flow has to overcome a lot of problems to be effective. Among them are occlusion of distant details, lack of directional and depth hints and occlusion. We present methods which address these problems for real-time graphic representations applicable in virtual environments. We use dashtubes, i.e., animated, opacity-mapped streamlines, as a visualization icon for 3D-flow visualization. We present a texture mapping technique to keep the level of texture detail along a streamline nearly constant even when the velocity of the flow varies considerably. An algorithm is described which distributes the dashtubes evenly in space. We apply magic lenses and magic boxes as interaction techniques for investigating densely filled areas without overwhelming the observer with visual detail. Implementation details of these methods and their integration in our virtual environment conclude the paper.

Collaborative visualization in augmented reality

The authors discuss Studierstube, a low-cost augmented reality system. The system features true stereoscopy, 3D interaction, individual viewpoints and customized views for multiple users, and unhindered natural collaboration.

Fast calibration for augmented reality

Augmented Reality overlays computer generated images over the real world. These images have to be generated using transformations which correctly project a point in virtual space onto its corresponding point in the real world. We present a simple and fast calibration scheme for head-mounted displays (HMDs), which does not require additional instrumentation or complicated procedures. The user is interactively guided through the calibration process, allowing even inexperienced users to calibrate the display to their eye distance and head geometry. The calibration is stable - meaning that slight errors made by the user do not result in gross miscalibrations - and easily applicable for see-through and video-based HMDs.

Collaborative augmented reality: exploring dynamical systems

We present collaborative scientific visualization in STUDIERSTUBE. STUDIERSTUBE is an augmented reality system that has several advantages over conventional desktop and other virtual reality environments, including true stereoscopy, 3D-interaction, individual viewpoints and customized views for multiple users, unhindered natural collaboration and low cost. We demonstrate the application of this concept for the interaction of multiple users and illustrate it with several visualizations of dynamical systems in DynSys3D, a visualization system running on top of AVS.

Comprehensive calibration and registration procedures for augmented reality

Augmented Reality - best described as adding computer-generated virtual content to the real environment – needs more adjustments to work properly than immersive virtual environments. To be perceived as an augmentation of reality, the virtual environment has to be properly aligned to the real world. This registration process has to be done at least once for every hardware set-up, but may have to be repeated in part or completely for each user, prop or device to be included both in the real and the virtual world. In this paper, we propose a comprehensive process for registration and calibration tasks necessary to implement correct augmentation. This includes procedures for calibrating projective and head-mounted displays, tracking systems, tracked input devices and props. Our method unifies the necessary tasks of world-toaugmentation alignment, display calibration and registration of tracked and static props in one, interactive set-up process, which can easily be conducted by the untrained user.

Strolling Through Cyberspace With Your Hands In Your Pockets: Head Directed Navigation In Virtual Environments

Head-Directed Navigation is a simple and efficient method for navigating large virtual spaces. For walkthrough applications such as architectural visualization or games, the user is often required to cover simulated distances. In doing so, inexperienced users often have a hard time learning complicated navigation patters with 3-D mice or similar input devices. In large virtual worlds, this frequently leads to disorientation. With head directed navigation, the user navigates the virtual environment only by orienting his or her head. An orientation tracker mounted on the head-mounted display worn by the user is used to derive the navigation commands. Besides the approach’s simplicity, the user’s hands are left free for other tasks.

Practical calibration procedures for augmented reality

Augmented Reality overlays computer generated images over the real world. This requires precise knowledge of the viewing projection of the headmounted display (HMD) and its position. Most of the previously published methods are complicated or use special equipment for the calibration process. We present a collection of calibration methods usable for fast and easy calibration of camera parameters, object/camera to tracker transformations, and image rectification, which do not need additional instrumentation or complicated procedures. They are applicable for both see-through and videobased HMDs and have already been successfully implemented in the Studierstube collaborative augmented environment.