Direct volume-rendering has proven to be an effective and flexible visualization method for 3D scalar fields. Transfer functions are fundamental

Most direct volume renderings produced today employ one-dimensional transfer functions, which assign color and opacity to the volume based solely on the single scalar quantity which comprises the dataset. Though they have not received widespread attention, multi-dimensional transfer functions are a very effective way to extract specific material boundaries and convey subtle surface properties. However, identifying good transfer functions is difficult enough in one dimension, let alone two or three dimensions. This paper demonstrates an important class of three-dimensional transfer functions for scalar data (based on data value, gradient magnitude, and a second directional derivative), and describes a set of direct manipulation widgets which make specifying such transfer functions intuitive and convenient. We also describe how to use modern graphics hardware to interactively render with multi-dimensional transfer functions. The transfer functions, widgets, and hardware combine to form a powerful system for interactive volume exploration.

In this paper we systematically develop a novel, interactive sculpting framework founded upon subdivision solids and physics-based modeling. In contrast with popular subdivision surfaces, subdivision solids have the unique advantage offering both the boundary representation and the interior material of a solid object. We unify the geometry of subdivision solids with the principle of physicsbased models and formulate dynamic subdivision solids. Dynamic subdivision solids respond to applied forces in a natural and predictive manner and give the user the illusion of manipulating semielastic virtual clay. We have developed a real-time sculpting system that provides the user with a wide array of intuitive sculpting toolkits. The flexibility of the subdivision solid approach allows users to easily modify the topology of sculpted objects, while the inherent physical properties are exploited to provide a natural interface for direct, force-based deformation. More importantly, our sculpting sy...

Multimodal interfaces have been shown to increase user performance for a variety of tasks. We have been investigating the synergistic benefits of haptic scientific visualization using an integrated, semi-immersive virtual environment. The Visual Haptic Workbench provides multimodal interaction; immersion is enhanced by head and hand tracking, haptic feedback, and additional audio cues. We present the motivation and design goals for this system, discuss its current implementation, and describe some initial applications. Preliminary results indicate that visualization combined with haptic rendering intuitively conveys the salient characteristics of scientific data.

Standard free-form splines such as B-splines and NURBS are widely employed in a wide range of CAD/CAM systems. Conventional geometric modeling and design techniques using these popular splines often requires tedious control-point manipulation and/or painstaking constraint specification (for functional requirements) via unnatural mouse-based computer interfaces. In this paper, we propose a novel and natural haptic interface and present a physics-based geometric modeling approach that supports the interactive sculpting of spline-based virtual material. Our desktop modeling system permits both expert and non-expert users to interactively deform virtual materials with real properties using force feedback. Using commercially available (and low-cost) haptic devices, modelers can feel the physically realistic presence of virtual spline objects such as B-splines throughout the design process. Our haptics-based B-spline is a special case of more powerful dynamic NURBS (D-NURBS) models. We develop various haptic sculpting tools to expedite the deformation of B-spline surfaces with haptic feedback and constraints. The most significant contribution of this paper is that point, normal, and curvature constraints can be specified interactively and modified naturally using forces. To achieve the real-time sculpting performance, we devise a novel dual representation for B-spline surfaces in both physical and mathematical space: the physics-based mass-spring model is mathematically constrained by the B-spline surface throughout the sculpting session. We envision that the integration of haptics with traditional computer-aided design makes it possible to realize all the potential offered by both haptic sculpting and physics-based modeling in computer-integrated design, vir...

Abstract. This paper presents Virtual Clay as a novel, interactive, dynamic, haptics-based deformable solid of arbitrary topology. Our Virtual Clay methodology is a unique, powerful visual modeling paradigm which is founded upon the integration of (1) deformable models, (2) free-form, spline-based solids, (3) procedural subdivision solids of arbitrary topology, and (4) dynamic objects governed by physical laws. Solid geometry exhibits much greater modeling potential and superior advantages to popular surface-based techniques in visual computing. This is primarily because a CAD-based solid representation of a real-world physical object is both geometrically accurate and topologically unambiguous. We first introduce the concept of Virtual Clay based on dynamic subdivision solids. Then, we formulate the mathematics of Virtual Clay through the integration of the geometry of subdivision solids with the principle of physics-based CAGD. Our Virtual Clay models respond to applied forces in a natural and predictive manner and offer the user the illusion of manipulating semi-elastic clay in the real world. We showcase example sculptures created with our Virtual Clay sculpting environment, which is equipped with a large variety of real-time, intuitive sculpting toolkits. The versatility of our Virtual Clay techniques allows users to modify the topology of sculpted objects easily, while the inherent physical properties are exploited to provide a natural interface for direct, force-based deformation. More importantly, our sculpting system supports natural haptic interaction to provide the user with a realistic sculpting experience. It is our hope that our Virtual Clay graphics system can become a powerful tool in graphics, computer vision, animation, computer art, interactive techniques, and virtual environments.

Interaction in three dimensional virtual environments is difficult, often resulting in physical or mental fatigue. Haptic interfaces have previously been employed with 2D and 2.5D desktop metaphors in order to improve targeting performance. This paper extends the principle to a 3D environment targeting task. Subjects completed a targeting task with and without haptic feedback, in the form of "virtual magnets" that physically attract the user towards targets in the environment, and with and without the provision of stereo depth cues via a stereo emitter and shutter glasses. It was found that the virtual magnets improved subjects accuracy, but did not improve the time taken to reach the target. Stereo cues improved both the subjects' spatial accuracy, and significantly improved the temporal measure of performance.

This paper examines the use of motorized physical sliders with position and force as input and output parameters for tangible human computer interaction. Firstly, we present an analogue platform. It was used to realize two proof-ofconcept applications: one for learning system dynamics as part of physics education and the second for interaction with music loops. Based on the insight gained with the analogue platform and the two applications, we took the first steps towards a digital platform, also presented here. More generally, the paper presents socalled haptic modes, which may be generated using force feedback control of motorized sliders. The paper also briefly presents parts of the underlying software and hardware which was designed and realized as part of this project. Author Keywords HCI, User interface design, physical prototyping, haptic

A vital requirement for a successful software framework for digital storytelling is that it takes the abilities and backgroundof the story authors into account. Dedicatedtools shouldsupport authors in expressing their stories within this framework at an adequate level and point out an according authoring process for digital stories. The software framework shouldprovide communication interfaces between technology experts, storytelling experts andapplication domain-experts. These requirements are similar to the ones already encountered when setting up a framework for interactive training applications. We present a concept how component andframework methodologies from software engineering as well as concepts from artificial intelligence can foster the design of such a software framework. The software architecture of our proposed framework is discussed as well as the according authoring process and tools. An implementation of our concept is described and lessons learned during using this framework in the application domain of emergency training are addressed. Although the framework has been applied for training purposes in particular, it can be usedas a basis for a digital storytelling framework in general. r 2002 Elsevier Science Lt . All rights reserve . 1.

Many haptic rendering problems can be expressed in terms of constraints on the motion of a proxy within a virtual environment. This principle is well established for surface rendering, and can also be applied to other types of haptic interaction. A key problem in general constraint based rendering is combining constraints from several sources into a single unified constraint. This paper describes some work in progress toward developing a mathematical framework for manipulating motion constraint equations, and in particular the derivation of a combination algebra for constraints. This work could lead to a system for 6DOF rendering involving non-trivial proxy shapes.