Robert van Liere

A multimodal virtual reality interface for 3D interaction with VTK

The object-oriented visualization Toolkit (VTK) is widely used for scientific visualization. VTK is a visualization library that provides a large number of functions for presenting three-dimensional data. Interaction with the visualized data is controlled with two-dimensional input devices, such as mouse and keyboard. Support for real three-dimensional and multimodal input is non-existent. This paper describes VR-VTK: a multimodal interface to VTK on a virtual environment. Six degree of freedom input devices are used for spatial 3D interaction. They control the 3D widgets that are used to interact with the visualized data. Head tracking is used for camera control. Pedals are used for clutching. Speech input is used for application commands and system control. To address several problems specific for spatial 3D interaction, a number of additional features, such as more complex interaction methods and enhanced depth perception, are discussed. Furthermore, the need for multimodal input to support interaction with the visualization is shown. Two existing VTK applications are ported using VR-VTK to run in a desktop virtual reality system. Informal user experiences are presented.

An Image-Warping Architecture for VR: Low Latency versus Image Quality

Designing low end-to-end latency system architectures for virtual reality is still an open and challenging problem. We describe the design, implementation and evaluation of a client-server depth-image warping architecture that updates and displays the scene graph at the refresh rate of the display. Our approach works for scenes consisting of dynamic and interactive objects. The end-to-end latency is minimized as well as smooth object motion generated. However, this comes at the expense of image quality inherent to warping techniques. We evaluate the architecture and its design trade-offs by comparing latency and image quality to a conventional rendering system. Our experience with the system confirms that the approach facilitates common interaction tasks such as navigation and object manipulation.

A comparison between coral colonies of the genus Madracis and simulated forms

In addition to experimental studies, computational models provide valuable information about colony development in scleractinian corals. Using our simulation model, we show how environmental factors such as nutrient distribution and light availability affect growth patterns of coral colonies. To compare the simulated coral growth forms with those of real coral colonies, we quantitatively compared our modelling results with coral colonies of the morphologically variable Caribbean coral genus Madracis. Madracis species encompass a relatively large morphological variation in colony morphology and hence represent a suitable genus to compare, for the first time, simulated and real coral growth forms in three dimensions using a quantitative approach. This quantitative analysis of three-dimensional growth forms is based on a number of morphometric parameters (such as branch thickness, branch spacing, etc.). Our results show that simulated coral morphologies share several morphological features with real coral colonies (M. mirabilis, M. decactis, M. formosa and M. carmabi). A significant correlation was found between branch thickness and branch spacing for both real and simulated growth forms. Our present model is able to partly capture the morphological variation in closely related and morphologically variable coral species of the genus Madracis.

Comparing Aimed Movements in the Real World and in Virtual Reality

The study of aimed movements has a long history, starting at least as far back as 1899 when Wood-worth proposed a two-component model in which aimed movements are broken into an initial ballistic phase and an additional control phase. In this paper, we use Wood-worths model for experimentally comparing aimed movements in the real world with those in a virtual environment. Trajectories from real world movements have been collected and compared to trajectories of movements taken from a virtual environment. From this, we show that significant temporal differences arise in both the ballistic and control phases, but the difference is much larger in the control phase; users improvement is relatively greater in the virtual world than in the real world. They progress more in ballistic phase in the real world, but more in correction phase in the virtual world. These results allow us to better understand the pointing tasks in virtual environments.

Data Visualization 2000

When dealing with a graph, any visualization strategy must rely on a layout procedure at least to initiate the process. Because the visualization process evolves within an interactive environment the choice of this layout procedure is critical and will often be based on efficiency. This paper compares two popular layout strategies, one based on the extraction of a spanning tree, the other based on edge crossing minimization of directed acyclic graphs. The comparison is made based on a large number of experimental evidence gathered through random graph generation. The main conclusion of these experiments is that, contrary to the popular belief, usage of edge crossing minimization algorithms may be extremely useful and advantageous, even under the heavy requirements of information visualization.

Experiencing 3D interactions in virtual reality and augmented reality

We demonstrate basic 2D and 3D interactions in both a Virtual Reality (VR) system, called the Personal Space Station, and an Augmented Reality (AR) system, called the Visual Interaction Platform. Since both platforms use identical (optical) tracking hardware and software, and can run identical applications, users can experience the effect of the way the systems present their information to them (as VR or AR). Since the systems use state-of-the-art tracking technology, the users can also experience the opportunities and limitations offered by such technology at first hand. Such hands-on experience is expected to enrich the discussion on the role that VR and AR systems (with optical tracking) could and/or should play within Ambient Intelligence.

Revisiting path steering for 3D manipulation tasks

The law of path steering, as proposed by Accot and Zhai, describes a quantitative relationship between human temporal performance and the paths spatial characteristics. The steering law is formulated as a continuous goal crossing task, in which a large number of goals are crossed along the path. The steering law has been verified empirically for locomotion, in which a virtual driving task through straight and circular paths was performed.

Special section: IEEE Virtual Reality (VR) 2009: A shared-scene-graph image-warping architecture for VR: Low latency versus image quality

Designing low end-to-end latency system architectures for virtual reality is still an open and challenging problem. We describe the design, implementation and evaluation of a client-server depth-image warping architecture that updates and displays the scene graph at the refresh rate of the display. Our approach works for scenes consisting of dynamic and interactive objects. The end-to-end latency is minimized as well as smooth object motion generated. However, this comes at the expense of image quality inherent to warping techniques. To improve image quality, we present a novel way of detecting and resolving occlusion errors due to warping. Furthermore, we investigate the use of asynchronous data transfers to increase the architectures performance in a multi-GPU setting. Besides polygonal rendering, we also apply image-warping techniques to iso-surface rendering. Finally, we evaluate the architecture and its design trade-offs by comparing latency and image quality to a conventional rendering system. Our experience with the system confirms that the approach facilitates common interaction tasks such as navigation and object manipulation.

Perception of mechanically and optically simulated bumps and holes

In this article, we investigate the perception of optically simulated haptic feedback. The perception of optically and mechanically simulated bumps and holes was tested experimentally. In an earlier article, we have described the active cursor technique, a method to simulate haptic feedback optically without resorting to special mechanical force feedback devices, commonly applied to produce haptic percepts in computer interfaces. The operation of the force feedback device is substituted by tiny displacements on the cursor position relative to the intended force. This method exploits the domination of the visual over the haptic modality. Results show that people can recognize optically simulated bump and hole structures and that active cursor displacements influence the haptic perception of bumps and holes. Depending on the simulated strength of the force, optically simulated haptic feedback can take precedence over mechanically simulated haptic feedback and also the other way around. When optically simulated and mechanically simulated haptic feedback counteract each other, however, the weight attributed to each source of haptic information differs from user to user. It is concluded that active cursor displacements can be used to simulate the operation of mechanical force feedback devices.

Insight into 3D goal-directed movements through a division into meaningful movement phases

The measures that are currently used to evaluate users’ performances on interaction tasks in virtual environments often do not provide sufficient information for how to improve these interactions. The current paper proposes a new method for analyzing 3D goal-directed movements based on dividing them into meaningful phases. We apply the method to experimental data that we have collected earlier for a 3D task that resembles a standardized 2D multi-directional pointing task (ISO 9241-9). Our analysis demonstrates how a more detailed insight into 3D goal-directed movements can be gained. We claim that this analysis can help to better identify weak and strong points of input devices or interaction techniques.