Jurriaan D. Mulder

A survey of computational steering environments

Computational steering is a powerful concept that allows scientists to interactively control a computational process during its execution. In this paper, a survey of computational steering environments for the on-line steering of ongoing scientific and engineering simulations is presented. These environments can be used to create steerable applications for model exploration, algorithm experimentation, or performance optimization. For each environment the scope is identified, the architecture is summarized, and the concepts of the user interface is described. The environments are compared and conclusions and future research issues are given.

Computational steering

The traditional cycle in simulation is to prepare input, execute a simulation, and to visualize the results as a post-processing step. However, more insight and a higher productivity can be achieved if these activities are done simultaneously. This is the underlying idea of Computational Steering: researchers change parameters of their simulation on the y and immediately receive feedback on the eeect. In this paper the Computational Steering Environment, CSE , is described. We discuss the requirements of computational steering environment, its relation with high performance computing and networking, and show an application of its use.

Optical tracking using projective invariant marker pattern properties

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.

An affordable optical head tracking system for desktop VR/AR systems

We present an affordable optical head tracking system for desktop-like VR/AR environments. The generic and specific head tracking requirements for these type of environments are de ned, as well as the relaxations such environments put on head tracking systems. The presented head tracker is based on two low-cost, commodity FireWire cameras that track a simple 3D dot pattern. It is shown that the tracker provides high accuracy, an update rate of 30 updates per second, a low computational load, and a moderate delay of 66 ms. It is competitive to commercially available, moderate-cost head tracking systems yet for substantially lower costs.

Pixel masks for screen-door transparency

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.

Fast perception-based depth of field rendering

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.

Enhancing fish tank VR

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.

Optical tracking and calibration of tangible interaction devices

In this paper, a novel optical tracking and object calibration system is presented for the recognition and pose estimation of tangible interaction devices for virtual and augmented reality systems. The calibration system allows a user to automatically generate models of the relative positions of point-shaped markers attached to interaction devices, simply by moving them in front of the cameras. There are virtually no constraints on the shape of interaction devices. The tracking method takes the calibrated models as input, and recognizes devices by subgraph matching. Both the calibration and tracking methods can handle partial occlusion. Results show the proposed techniques are efficient, accurate, and robust.

Spatial input device structure and bimanual object manipulation in virtual environments

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 devices 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 users 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.

Optical Tracking and Automatic Model Estimation of Composite Interaction Devices

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