This paper compares two separately developed systems for monitoring activities to business contracts, describes how we integrated them and exploits the lessons learned from this process to identify a core set of requirements for a Business Contract Language (BCL). Concepts in BCL needed for contract monitoring include: the expression of coordinated concurrent actions; obliged, permitted and prohibited actions; rich timeliness expressions such as sliding windows; delegations; policy violations; contract termination/renewal conditions and reference to external data/events such as change in interest rates. The aim of BCL is to provide sufficient expressive power to describe contracts, including conditions which specify real-time processing, yet be simple enough to retain a human-oriented style for expressing contracts.

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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.

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.

There are many real-world applications of Virtual Reality that require the construction of complex and accurate three-dimensional models, suitably structured for interactive manipulation. In this paper, we present semi-automatic methods that allow such environments to be quickly and easily built from photographs taken with uncalibrated cameras, and illustrate the techniques by application to the real-world problem of scene-of-crime reconstruction.

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.