Real-time finite element (FE) analysis can be used to represent complex deformable geometries in virtual environments. The need for accurate surgical simulation has spurred the development of many of the new real-time FE methodologies that enable haptic support and real-time deformation. These techniques are computationally intensive and it has proved to be a challenge to achieve the high modeling resolutions required to accurately represent complex anatomies. The authors present a new real-time methodology based on linear FE analysis that is appropriate for a wide range of surgical simulation applications. A methodology is proposed that is characterized by high model resolution, low preprocessing time, unrestricted multipoint surface contact, and adjustable boundary conditions. These features make the method ideal for modeling suturing, which is an element common to almost every surgical procedure. This paper describes constraints in the context of a Suturing Simulator currently being developed by the authors.

This paper demonstrates how non-isomorphic rotational mappings and interaction techniques can be designed and used to build effective spatial 3D user interfaces. In this paper, we develop a mathematical framework allowing us to design non-isomorphic 3D rotational mappings and techniques, investigate their usability properties, and evaluate their user performance characteristics. The results suggest that non-isomorphic rotational mappings can be an effective tool in building high-quality manipulation dialogs in 3D interfaces, allowing our subjects to accomplish experimental tasks 13% faster without a statistically detectable loss in accuracy. The current paper will help interface designers to use non-isomorphic rotational mappings effectively.

The acceptance of virtual environment (VE) technology requires scrupulous optimization of the most basic interactions in order to maximize user performance and provide efficient and enjoyable virtual interfaces. Motivated by insufficient understanding of the human factors design implications of interaction techniques and tools for virtual interfaces, this paper presents results of a formal study that compared two basic interaction metaphors for egocentric direct manipulation in VEs, virtual hand and virtual pointer, in object selection and positioning experiments. The goals of the study were to explore immersive direct manipulation interfaces, compare performance characteristics of interaction techniques based on the metaphors of interest, understand their relative strengths and weaknesses, and derive design guidelines for practical development of VE applications.

Developing virtual reality (VR) applications which enable actual work over a period of time requires optimization of the most basic interactions, such as object manipulation, so that the immersed participant can concentrate on higher-level tasks rather than on lowlevel motor activities. This paper presents a framework and experimental testbed for studies of VR object manipulation techniques. The framework provides a systematic task analysis of immersive manipulation and suggests a user-specific non-Euclidean system for the measurement of VR spatial relationships. The Virtual Reality Manipulation Assessment Testbed (VRMAT) is a practical implementation of the framework and is a flexible tool allowing in-depth experimental studies of immersive manipulation. Pilot studies have been conducted to evaluate this framework and testbed and to establish a baseline for further development. Keywords: immersive virtual reality, VR user interfaces, VR manipulation techniques, user studies, experimen...

The Go-Go immersive interaction technique uses the metaphor of interactively growing the user’s arm and non-linear mapping for reaching and manipulating distant objects. Unlike others, our technique allows for seamless direct manipulation of both nearby objects and those at a distance.