Retrieving information presented visually is difficult for visually disabled users. Current accessibility technologies, such as screen readers, fail to convey presentational layout or structure. Information presented in graphs or images is almost impossible to convey through speech alone. In this paper, we present the results of an experimental study investigating the role of touch (haptic) and auditory cues in aiding structure recognition when visual presentation is missing. We hypothesize that by guiding users toward nodes in a graph structure using force fields, users will find it easier to recognize overall structure. Nine participants were asked to explore simple 3D structures containing nodes (spheres or cubes) laid out in various spatial configurations and asked to identify the nodes and draw their overall structure. Various combinations of haptic and auditory feedback were explored. Our results demonstrate that haptic cues significantly helped participants to quickly recognize nodes and structure. Surprisingly, auditory cues alone did not speed up node recognition; however, when they were combined with haptics both node identification and structure recognition significantly improved. This result demonstrates that haptic feedback plays an important role in enabling people to recall spatial layout.

Capturing detailed surface geometry currently requires specialized equipment such as laser range scanners, which despite their high accuracy, leave gaps in the surfaces that must be reconciled with photographic capture for relighting applications. Using only a standard digital camera and a single view, we present a method for recovering models of predominantly diffuse textured surfaces that can be plausibly relit and viewed from any angle under any illumination. Our multiscale shape-from-shading technique uses diffuse-lit/flash-lit image pairs to produce an albedo map and textured height field. Using two lighting conditions enables us to subtract one from the other to estimate albedo. In the absence of a flash-lit image of a surface for which we already have a similar exemplar pair, we approximate both albedo and diffuse shading images using histogram matching. Our depth estimation is based on local visibility. Unlike other depth-from-shading approaches, all operations are performed on the diffuse shading image in image space, and we impose no constant albedo restrictions. An experimental validation shows our method works for a broad range of textured surfaces, and viewers are frequently unable to identify our results as synthetic in a randomized presentation. Furthermore, in side-by-side comparisons, subjects found a rendering of our depth map equally plausible to one generated from a laser range scan. We see this method as a significant advance in acquiring surface detail for texturing using a standard digital camera, with applications in architecture, archaeological reconstruction, games and special effects.

We present a system that enables, for the first time, effective transatlantic cooperative haptic manipulation of objects whose motion is computed using a physically-based model. We propose a technique for maintaining synchrony between simulations in a peer-to-peer system, while providing responsive direct manipulation for all users. The effectiveness of this approach is determined through extensive user trials involving concurrent haptic manipulation of a shared object. A CAD assembly task, using physically-based motion simulation and haptic feedback, was carried out between the USA and the UK with network latencies in the order of 120ms. We compare the effects of latency on synchrony between peers over the Internet with a low latency (0.5ms) local area network. Both quantitatively and qualitatively, when using our technique, the performance achieved over the Internet is comparable to that on a LAN. As such, this technique constitutes a significant step forward for distributed haptic collaboration

Collaborative virtual environments (CVEs) enable two or more people, separated in the real world, to share the same virtual “space.” They can be used for many purposes, from teleconferencing to training people to perform assembly tasks. Unfortunately, the effectiveness of CVEs is compromised by one major problem: the delay that exists in the networks linking users together. Whilst we have a good understanding, especially in the visual modality, of how users are affected by delayed feedback from their own actions, little research has systematically examined how users are affected by delayed feedback from other people, particularly in environments that support haptic (force) feedback. The current study addresses this issue by quantifying how increasing levels of latency affect visual and haptic feedback in a collaborative target acquisition task. Our results demonstrate that haptic feedback in particular is very sensitive to low levels of delay. Whilst latency affects visual feedback from 50 ms, it impacts on haptic task performance 25 ms earlier, and causes the haptic measures of performance deterioration to rise far more steeply than visual. The “impact-perceive-adapt” model of user performance, which considers the interaction between performance measures, perception of latency, and the breakdown of perception of immediate causality, is proposed as an explanation for the observed pattern of performance.

Network architectures for collaborative virtual reality have traditionally been dominated by client-server and peer-to-peer approaches, with peer-to-peer strategies typically being favored where minimizing latency is a priority, and client-server where consistency is key. With increasingly sophisticated behavior models and the demand for better support for haptics, we argue that neither approach provides sufficient support for these scenarios and, thus, a hybrid architecture is required. We discuss the relative performance of different distribution strategies in the face of real network conditions and illustrate the problems they face. Finally, we present an architecture that successfully meets many of these challenges and demonstrate its use in a distributed virtual prototyping application which supports simultaneous collaboration for assembly, maintenance, and training applications utilizing haptics.

No abstract available.

The central goal in Distributed Virtual Environments (DVEs) is to provide an experience of the shared world that is perceptually plausible for the immersed user. This has to be achieved in the face of network issues such as bandwidth limitations and latencies which make total synchronism impossible. Techniques have been devised to help; some optimise network use by limiting what is transmitted, others try to disguise the effects of network 'glitches' at the user's client machine - for example smoothing policies. To date such techniques tend to be system-based rather than user-oriented. Yet there is an active body of psychological research, for example in visual attention, which has successfully been employed by the graphics community to yield better perceived results for a given resource. Immersive DVEs are even more critically dependent upon the users' perceived experience. We may expect therefore that such 'psychologically' oriented approaches have even more to offer here. In this paper a visual attention model which exploits the peculiarities of the human visual system is presented. It is based on previous work, and on a series of carefully designed experiments which are used to guide the implementation of the model and to design architectures for DVEs. The proposed architectures are then tested using different DVE experimental applications, which include a highly populated virtual city. The results demonstrate that the characteristics of the human visual system can be exploited to improve network usage and generate a more perceptually plausible environment in the face of incomplete synchronisation.

Camera tracking is a fundamental requirement for video-based augmented reality applications. The ability to accurately calculate the intrinsic and extrinsic camera parameters for each frame of a video sequence is essential if synthetic objects are to be integrated into the image data in a believable way. In this paper, we present an accurate and reliable approach to camera calibration for off-line video-based augmented reality applications. We first describe an improved feature tracking algorithm, based on the widely used Kanade-Lucas-Tomasi tracker. Estimates of inter-frame camera motion are used to guide tracking, greatly reducing the number of incorrectly tracked features. We then present a robust hierarchical scheme that merges sub-sequences together to form a complete projective reconstruction. Finally, we describe how RANSAC-based random sampling can be applied to the problem of self-calibration, allowing for more reliable upgrades to metric geometry. Results of applying our calibration algorithms are given for both synthetic and real data.

We present a Hybrid Geometric-Image Based Rendering (HGIBR) system for displaying very complex geometrical models at interactive frame rates. Our approach replaces distant geometry with a combination of image-based representations and geometry, while rendering nearby objects from geometry. Reference images are computed on demand, which means that no pre-processing, or additional storage are necessary. We present results for a massive model of a whole offshore gas platform, to demonstrate that interactive frame rates can be maintained using the HGIBR approach. Our implementation runs on a pair of PCs, using commodity graphics hardware for fast 3D warping.

Photometric reconstruction is the process of estimating the illumination and surface reflectance properties of an environment, given a geometric model of the scene and a set of photographs of its surfaces. For mixed-reality applications, such data is required if synthetic objects are to be correctly illuminated or if synthetic light sources are to be used to re-light the scene. Current methods of estimating such data are limited in the practical situations in which they can be applied, due to the fact that the geometric and radiometric models of the scene which are provided by the user must be complete, and that the position (and in some cases, intensity) of the light sources must also be specified a-priori. In this paper, a novel algorithm is presented which overcomes these constraints, and allows photometric data to be reconstructed in less restricted situations. This is achieved through the use of virtual light sources which mimic the effect of direct illumination from unknown luminaires, and indirect illumination reflected off unknown geometry. The intensity of these virtual light sources and the surface material properties are estimated using an iterative algorithm which attempts to match calculated radiance values to those observed in photographs. Results are presented for both synthetic and real scenes that show the quality of the reconstructed data and its use in off-line mixed-reality applications.

This paper presents a case study of navigation and manipulation in a large, geometrically complex, virtual environment representing an off‐shore gas platform. Our approach is based on a combined force‐field navigation and collision detection algorithm. After describing the basic algorithm, we extend and apply it to a real‐time simulation of two avatars carrying a third avatar on a stretcher. The extensions include a probing technique, using a virtual foot and simulated gravity, to permit ascending and descending stairs and ladders. A set of constraints between the stretcher and avatars enforces realistic lifting positions. The simulation is controlled interactively with a hand‐held 3D mouse. The force fields assist the user in manoeuvring through tight spaces, while collision detection guarantees that neither the stretcher nor the avatars can pass through obstructions, such as pipe‐work or hand‐rails. Results are presented for a case study of a complete simulation running on a PC with a moderately fast 3D graphics card. These demonstrate that the method delivers a useful frame rate for the off‐shore gas platform.

The authors describe a novel algorithm for computing view-independent finite element radiosity solutions on distributed shared memory parallel architectures. Our approach is based on the notion of a subiteration being the transfer of energy from a single source to a subset of the scene's receiver patches. By using an efficient queue based scheduling system to process these subiterations, we show how radiosity solutions can be generated without the need for processor synchronization between iterations of the progressive refinement algorithm. The only significant source of interprocessor communication required by our method is for visibility calculations. We also describe a perceptually driven approach to visibility estimation, which employs an efficient volumetric grid structure and attempts to reduce the amount of interprocessor communication by approximating visibility queries between distant patches. Our algorithm also eliminates the need for dynamic load balancing until the end of the solution process and is shown to achieve a superlinear speedup in many situations.

This paper describes a publicly available virtual reality (VR) system, GNU/MAVERIK, which forms one component of a complete 'VR operating system'. We give an overview of the architecture of MAVERIK, and show how it is designed to use application data in an intelligent way, via a simple, yet powerful, callback mechanism which supports an object-oriented framework of classes, objects and methods. Examples are given which illustrate different uses of the system, and typical performance levels.

This paper presents a new technique for controlling a user's navigation in a virtual environment.The approach introduces artificial force fields which act upon the user's virtual body such that he is guided around obstacles, rather than penetrating or colliding with them.The technique is extended to incorporate gravity into the environment.The problem of negotiating stairs during a walk-through has also been investigated with the new approach.Human subjects were tested in experiments in which they experienced three different kinds of navigation: unconstrained, simple constrained and assisted by force fields.Theresults demonstrate that the force-field technique is an effective approach for effective, comfortable navigation.

We present a new approach to radiosity simulation that uses perceptually‐based measures to control the generation of view‐independent radiosity solutions. This enables computational effort to be moved away from areas that are deemed to have a visually insignificant effect on the solution's appearance, into those that are more noticeable. We achieve this with an a‐priori estimate of the real‐world adaptation luminance, and use a tone‐reproduction operator to transform luminance values to display colours during the solution process. The distance between two colours in a perceptually‐uniform colour space is then used as a numerical measure of their perceived difference. We describe an oracle that stops patch refinement once the difference between successive levels of elements becomes perceptually unnoticeable. We also show how the perceived importance of any potential shadow falling across a receiving element can be determined. This is then used to control the number of rays that are cast during visibility computations, giving reductions of almost 93% in the total number of rays required for a solution without any significant loss in image quality. Finally, we discuss how perceptual knowledge can be used to optimise the element mesh for faster interactive display and to save memory during computation.

Abstract This paper describes the results of experiments with accelerated ray tracing on a virtual shared‐memory parallel computer and attempts to determine whether this kind of architecture would be suitable for an interactive ray tracing system. The machine used, the Kendall Square Research KSR1, is described in sufficient detail for its novel features to be appreciated. The paper describes a new ray tracer written specifically to capitalise on the KSR1 's features. Models used in the experiments include well‐known test cases from the Haines database, permitting comparison with previously reported results. The results show that the program scales well up to 230 processors, and that with progressive rendering initial rendering times can be reduced to as little as 0.2 second on 32 processors.

Abstract The modelling of solid objects is becoming increasingly important in the application of computer graphics to a wide variety of problems, such as CAD/CAM, simulation, and molecular modelling. A variety of methods for rendering solid objects exists, including 2‐Buffer, Scanline and Ray Tracing. This paper is concerned with a scanline method for the production of still images of complex objects. The implementation of a scanline algorithm is discussed, in conjunction with a consideration of its performance in relation to the z‐buffer method. Many scanline methods cater only for a restricted class of primitives, such as polygons or spheres, whereas this implementation is a general purpose scanline algorithm capable of being extended to handle a variety of primitives. The primitives currently available are polygons, spheres, spheres swept along straight‐line trajectories, and cylinders. Polygonal models of cubes, cones and cylinders are also available. The approach is capable of dealing with “positive” and “negative” volumes, allowing objects with holes to be modelled and displayed. It has further been extended to cater for the inclusion of transparent objects into a scene, and consequently allows the modelling of coloured “glass” objects.

Interactive computer graphics programs have been developed to permit the clinical application of a new method of analysis of craniofacial discrepancies and its use for diagnosis and testing alternative treatment plans. The validity of the method has been tested statistically, and the programs have been used to formulate treatment plans for a number of orthodontic patients. Example results from the treatment planning are included.

A computer graphics system with refresh and storage displays, flat-bed plotter, digitizer and film recorder is described. The software structure comprises a device-independent, front-end graphics package and a driver program for each device. Two and three-dimensional vectors, hardware and software characters, transformations and windowing, picture segmentation, element and segment attributes, and input from interactive tools, such as a light-pen, are supported. The extent to which the system is used by different research groups shows that this is a very cost-effective way to provide computer graphics facilities.