Carla Maria Dal Sasso Freitas

Cooperative object manipulation in immersive virtual environments: framework and techniques

Cooperative manipulation refers to the simultaneous manipulation of a virtual object by multiple users in an immersive virtual environment. This paper describes a framework supporting the development of collaborative manipulation techniques, and example techniques we have tested within this framework. We describe the modeling of cooperative interaction techniques, methods of combining simultaneous user actions, and the awareness tools used to provide the necessary knowledge of partner activities during the cooperative interaction process. Our framework is based on a Collaborative Metaphor concept that defines rules to combine user interaction techniques. The combination is based on the separation of degrees of freedom between two users. Finally, we present novel combinations of two interaction techniques (Simple Virtual Hand and Ray-casting).

A formal description of multimodal interaction techniques for immersive virtual reality applications

Nowadays, designers of Virtual Reality (VR) applications are faced with the choice of a large number of different input and output devices leading to a growing number of interaction techniques. Usually VR interaction techniques are described informally, based on the actions users can perform within the VR environment. At implementation time, such informal descriptions (made at design time) yield to ambiguous interpretations by the developers. In addition, informal descriptions make it difficult to foresee the impact throughout the application of a modification of the interaction techniques. This paper discusses the advantages of using a formal description technique (called ICO) to model interaction techniques and dialogues for VR applications. This notation is presented via a case study featuring an immersive VR application. The case study is then used to show, through analysis of models, how the formal notation can help to ensure the usability, reliability and efficiency of virtual reality systems.

Broad-phase collision detection using semi-adjusting BSP-trees

The broad-phase step of collision detection in scenes composed of n moving objects is a challenging problem because enumerating collision pairs has an inherent O(n2) complexity. Spatial data structures are designed to accelerate this process, but often their static nature makes it difficult to handle dynamic scenes. In this work we propose a new structure called Semi-Adjusting BSP-tree for representing scenes composed of thousands of moving objects. An scheduling algorithm evaluates locations where the BSP-tree becomes unbalanced, uses several strategies to alter cutting planes, and defer updates based on their re-structuring cost. We show that the tree does not require a complete re-structuring even in highly dynamic scenes, but adjusts itself while maintaining desirable balancing and height properties.

Towards an integrated system for planning and assisting maxillofacial orthognathic surgery

Computer-assisted maxillofacial orthognathic surgery is an emerging and interdisciplinary field linking orthognathic surgery, remote signal engineering and three-dimensional (3D) medical imaging. Most of the computational solutions already developed make use of different specialized systems which introduce difficulties both in the information transfer from one stage to the others and in the use of such systems by surgeons. Trying to address such issue, in this work we present a common computer-based system that integrates proposed modules for planning and assisting the maxillofacial surgery. With that we propose to replace the current standard orthognathic preoperative planning, and to bring information from a virtual planning to the real operative field. The system prototype, including three-dimensional cephalometric analysis, static and dynamic virtual orthognathic planning, and mixed reality transfer of information to the operation room, is described and the first results obtained are presented.

Real-time volume rendering of time-varying data using a fragment-shader compression approach

The recent advance of graphics hardware allowed real-time volume rendering of structured grids using a 3D texturing approach. The next challenging problem is to extend the algorithms to time-varying volumetric data (4D functions), which consume more storage and are not directly supported in current graphics hardware. Here we present a new visualization technique that includes (1) a compression scheme of sparse 4D functions into 3D textures, and (2) a visualization algorithm that decompress the stored data from the 3D textures using the programmability of fragment shaders, allowing real-time visualization of such data. We illustrate the system in action with datasets resulting from computational fluid dynamics simulations.

On evaluating information visualization techniques

Evaluating user interfaces is usually accomplished to detect design problems in layout and interaction. One possible way to evaluate image quality in computer graphics is visual inspection by experts. Information visualization techniques are usually presented showing their use in experimental situations, employing some kind of analysis. Nevertheless, few works have specifically addressed the evaluation of such techniques. This work reports our results towards the definition of criteria for evaluating information visualization techniques, addressing the evaluation of visual representation and interaction mechanisms as a first step.

Design of multi-dimensional transfer functions using dimensional reduction

Direct volume rendering techniques allow visualization of volume data without extracting intermediate geometry. The mapping from voxel attributes to optical properties is performed by transfer functions which, consequently, play a crucial role in building informative images from the data. One-dimensional transfer functions, which are based only on a scalar value per voxel, often do not provide proper visualizations. On the other hand, multidimensional transfer functions can perform more sophisticated data classification, based on vectorial voxel signatures. The transfer function design is a non-trivial and unintuitive task, especially in the multi-dimensional case. In this paper we propose a multi-dimensional transfer function design technique that uses self-organizing maps to perform dimensional reduction. Our approach gives uniform treatment to volume data containing voxel signatures of arbitrary dimension, and allows the use of any type of voxel attribute as part of the voxel signatures.

Tasks and scenario-based evaluation of information visualization techniques

Usability evaluation of an information visualization technique can only be done by the joint evaluation of both the visual representation and the interaction techniques. This work proposes task models as a key element for carrying out such evaluations in a structured way. We base our work on a taxonomy abstracting from rendering functions supported by information visualization techniques. CTTE is used to model these abstract visual tasks as well as to generate scenarios from this model for evaluation purposes. We conclude that the use of task models allows generating test scenarios which are more effective than informal and unstructured evaluations.

User-Centered Evaluation of Information Visualization Techniques: Making the HCI-InfoVis Connection Explicit

In the last decade, the growing interest in evaluation of information visualization techniques is a clear indication that usability and user experience are very important quality criteria in this context. However, beyond this level of agreement there is much room for discussion about how to extend the variety of usability evaluation approaches for assessing information visualization techniques, and how to determine which ones are the most effective, and in what ways and for what purposes. In this chapter we take a user centered, Human-Computer Interaction-based perspective to discuss usability evaluation of information visualization techniques. We begin by presenting a singular view of the evolution of visualization techniques evaluation, briefly summarizing the main contributions of several works in this area since its humble beginning as a collateral activity until the recent growth of interest. Then, we focus on current issues related to such evaluations, particularly concerning the way they are designed and conducted, taking into account a background of well-known usability evaluation methods from HCI to help understanding why there are still open problems. A set of guidelines for a (more) user-centered usability evaluation of information visualization techniques is proposed and discussed. Our ultimate goal is to provide some insight regarding if and how sound ergonomic user-centered knowledge can be transferred to the information visualization context.

Cooperative object manipulation in collaborative virtual environments

Cooperative manipulation refers to the simultaneous manipulation of a virtual object by multiple users in an immersive virtual environment (VE). In this work, we present techniques for cooperative manipulation based on existing single-user techniques. We discuss methods of combining simultaneous user actions, based on the separation of degrees of freedom between two users, and the awareness tools used to provide the necessary knowledge of the partner activities during the cooperative interaction process. We also present a framework for supporting the development of cooperative manipulation techniques, which are based on rules for combining single user interaction techniques. Finally, we report an evaluation of cooperative manipulation scenarios, the results indicating that, in certain situations, cooperative manipulation is more efficient and usable than singleuser manipulation.