In this paper, a novel model-based optical tracking and model estimation system for composite interaction devices is presented. Devices consist of a set of linked segments, where each segment can have combinations of translational and rotational degrees of freedom (DOFs) relative to a parent segment. The system automatically constructs the geometric skeleton structure, DOF relations, and DOF constraints between segments. Pre-defined models are not required. The system supports segments with only a single marker, so that interaction devices can be small with a low number of markers. The model is computed in an offline procedure. The tracking method uses the obtained device model to recognize the device and reconstruct all DOF parameters describing the pose of each segment. The tracking method can handle partial occlusion. Results show the proposed techniques are efficient and robust

Complex 3D interaction tasks require the manipulation of a large number of input parameters. Spatial input devices can be constructed such that their structure reflects the task at hand. As such, somatosensory cues that a user receives during device manipulation, as well as a users expectations, are consistent with visual cues from the virtual environment. Intuitively, such a match between the device's spatial structure and the task at hand would seem to allow for more natural and direct interaction. However, the exact effects on aspects like task performance, intuitiveness, and user comfort, are yet unknown.The goal of this work is to study the effects of input device structure for complex interaction tasks on user performance. Two factors are investigated: the relation between the frame of reference of a user's actions and the frame of reference of the virtual object being manipulated, and the relation between the type of motion a user performs with the input device and the type of motion of the virtual object.These factors are addressed by performing a user study using different input device structures. Subjects are asked to perform a task that entails translating a virtual object over an axis, where the structure of the input device reflects this task to different degrees. First, the action subjects need to perform to translate the object is either a translation or a rotation. Second, the action is performed in the same frame of reference of the virtual object, or in a fixed, separately located, frame of reference.Results show that task completion times are lowest when the input device allows a user to make the same type of motion in the same coordinate system as the virtual object. In case either factor does not match, task completion times increase significantly. Therefore, it may be advantageous to structure an input device such that the relation between its frame of reference and the type of action matches the corresponding frame of reference and motion type of the virtual object being manipulated.

This paper describes the incorporation of realistic occlusion effects into mirror-based, stereoscopic co-location augmented reality display systems. By adding a light-blocking device in the form of an LCD panel underneath the semi-transparent mirror, the view on the physical world can be selectively blocked out such that virtual objects can fully occlude physical objects. Furthermore, by removing areas of the virtual objects rendered on the reflected display, physical objects seen through the semi-transparent mirror and the transmissive LCD panel appear to occlude these virtual objects. We describe the governing principles of the approach, and present an efficient algorithm for the generation of the occlusion masks with the use of vision-based scene reconstruction. Finally, a first prototype implementation of the system is presented.

To enable a user to perform Virtual Reality tasks as efficiently as possible, reducing tracking inaccuracies from noise and latency is crucial. Much work has been done to improve tracking performance by using predictive filtering methods. However, it is unclear what the benefits of each of these methods are in practice, which parameters influence their performance, and what the extent of this influence is. We present an analysis of various orientation prediction and filtering methods using various hand tasks and synthetic signals, and evaluate their performance in relation to each other. We identify critical parameters and analyse their influence on accuracy. Our results show that for the tested datasets, the use of an EKF is sufficient for orientation prediction in VR/AR.

Head coupled perspective is often considered to be an essential aspect of stereoscopic desktop virtual reality (VR) systems. Such systems use a tracking device to determine the user's head pose in up to six degrees of freedom (DOF). Users of desktop VR systems perform their task while sitting down and therefore the extent of head movements is limited. This paper investigates the validity of using a head tracking system for desktop VR that only tracks lateral head movement. Users performed a depth estimation task under full (six DOF) head tracking, lateral head tracking, and disabled head tracking. Furthermore, we considered stereoscopic and monoscopic viewing. Our results show that user performance was not significantly affected when incorporating only lateral head motion. Both lateral and full head tracking performed better than the disabled head tracking case.

In this paper, a new pattern based optical tracking method is presented for the recognition and pose estimation of input devices for virtual or augmented reality environments. The method is based on pencils of linefiducials, which reduces occlusion problems and allows for single camera pattern recognition and orientation estimation. Pattern recognition is accomplished using a projective invariant property of line pencils: the cross ratio. Orientation is derived from single camera line-plane correspondences, and position estimation is achieved using multiple cameras. The method is evaluated against a related point based tracking approach. Results show our method has lower latency and comparable accuracy, and is less sensitive to occlusion.

We describe a novel optical tracker algorithm for the tracking of interaction devices in virtual and augmented reality. The tracker uses invariant properties of marker patterns to efficiently identify and reconstruct the pose of these interaction devices. Since invariant properties are sensitive to noise in the 2D marker positions, an offline training session is used to determine deviations in these properties. These deviations are taken into account when searching for the patterns once the tracker is used.

Virtual environments have shown great promise as a research tool in science and engineering. In this paper, we study a classical problem in mathematics: that of approximating globally optimal Fekete point configurations. We found that a highly interactive virtual environment, combined with a time-critical computation, can provide valuable insight into the symmetry and stability of Fekete point configurations. We believe that virtual environments provide more natural interfaces to complex systems, allowing users to perceive, interpret and interact with the problem more rapidly.

Fish tank VR systems provide head coupled perspective projected stereo images on a display device of limited dimensions that resides at a fixed location. Therefore, fish tank VR systems provide only a limited virtual workspace. As a result, such systems are less suited for displaying virtual worlds that extend beyond the available workspace and depth perception problems arise when displaying objects (virtually) located on the edge of the workspace in between the viewer and the display screen. In this paper we present two techniques to reduce this disadvantage: cadre viewing and amplified head rotations. The first aims to eliminate the problems in depth perception for objects with negative parallax touching the screen surround. Subjective observations from an informal user study indicate a reduction of confusion in depth perception. The second provides a transparent navigation technique to allow users to view larger portions of the virtual world without the need for an additional input device to navigate. A user study shows it performs equally well when compared to a technique based on the use of an additional spatial input device.

Current algorithms to create depth of field (DOF) effects are either too costly to be applied in VR systems, or they produce inaccurate results. In this paper, we present a new algorithm to create DOF effects. The algorithm is based on two techniques: one of high accuracy and one of high speed but less accurate. The latter is used to create DOF effects in the peripheral viewing area where accurate results are not necessary. The first is applied to the viewing volume focussed at by the viewer. Both techniques make extensive use of rendering hardware, for texturing as well as image processing. The algorithm presented in this paper is an improvement over other (fast) DOF algorithms in that it is faster and provides better quality DOF effects where it matters most.

Rendering objects transparently gives additional insight in complex and overlapping structures. However, traditional techniques for the rendering of transparent objects such as alpha blending are not very well suited for the rendering of multiple transparent objects in dynamic scenes. Screen door transparency is a technique to render transparent objects in a simple and efficient way: no sorting is required and intersecting polygons can be handled without further preprocessing. With this technique, polygons are rendered through a mask: only where the mask is present, pixels are set. However, artifacts such as incorrect opacities and distracting patterns can easily occur if the masks are not carefully designed. The requirements on the masks are considered. Next, three algorithms are presented for the generation of pixel masks. One algorithm is designed for the creation of small (e.g. 4/spl times/4) masks. The other two algorithms can be used for the creation of larger masks (e.g. 32/spl times/32). For each of these algorithms, results are presented and discussed.

Computational steering is the ultimate goal of interactive simulation: researchers change parameters of their simulation and immediately receive feedback on the effect. We present a general and flexible graphics tool that is part of an environment for computational steering developed at CWI. It enables the researcher to interactively develop his own interface with the simulation. This interface is constructed with 3D parametrized geometric objects. The properties of the objects are parametrized to output data and input parameters of the simulation. The objects visualize the output of the simulation, while the researcher can steer the simulation by direct manipulation of the objects. Several applications of 3D computational steering are presented.