We introduce a new approach for the computation of viewindependent solutions to the diffuse global illumination problem in polyhedral environments. The approach combines ideas from hierarchical radiosity and discontinuity meshing to yield solutions that are accurate both numerically and visually. First, we describe a modified hierarchical radiosity algorithm that uses a discontinuitydriven subdivision strategy to achieve better numerical accuracy and faster convergence. Second, we present a new algorithm based on discontinuity meshing that uses the hierarchical solution to reconstruct an object-space approximation to the radiance function that is visually accurate. Our results show significant improvements over both hierarchical radiosity and discontinuity meshing algorithms.

Simulating realistic lighting and rendering complex scenes are usually considered separate problems with incompatible solutions. Accurate lighting calculations are typically performed using ray tracing algorithms, which require that the entire scene database reside in memory to perform well. Conversely, most systems capable of rendering complex scenes use scan-conversion algorithms that access memory coherently, but are unable to incorporate sophisticated illumination. We have developed algorithms that use caching and lazy creation of texture and geometry to manage scene complexity. To improve cache performance, we increase locality of reference by dynamically reordering the rendering computation based on the contents of the cache. We have used these algorithms to compute images of scenes containing millions of primitives, while storing ten percent of the scene description in memory. Thus, a machine of a given memory capacity can render realistic scenes that are an order of magnitude more complex than was previously possible.

Interactively manipulating the geometry of complex, globally illuminated scenes has to date proven an elusive goal. Previous attempts have failed to provide interactive updates of global illumination and have not been able to offer well-adapted algorithms controlling the frame rate. The need for such interactive updates of global illumination is becoming increasingly important as the field of application of radiosity algorithms widens. To address this need, we present a novel algorithm which provides interactive update rates of global illumination for complex scenes with moving objects. In the context of clustering for hierarchical radiosity, we introduce the idea of an implicit line-space hierarchy. This hierarchy is realized by augmenting the links between hierarchical elements (clusters or surfaces) with shafts, representing the set of lines passing through the two linked elements. We show how line-space traversal allows rapid identification of modified links, and simultaneous clean...

this paper, we present a system that exploits object-space, rayspace, image-space and temporal coherence to accelerate ray tracing. Our system uses per-surface interpolants to approximate radiance, while conservatively bounding error. The techniques we introduce in this paper should enhance both interactive and batch ray tracers.

We describe a system that computes radiosity solutions for polygonal environments much larger than can be stored in main memory. The solution is stored in and retrieved from a database as the computation proceeds. Our system is based on two ideas: the use of visibility oracles to find source and blocker surfaces potentially visible to a receiving surface; and the use of hierarchical techniques to represent interactions between large surfaces efficiently, and to represent the computed radiosity solution compactly. Visibility information allows the environment to be partitioned into subsets, each containing all the information necessary to transfer light to a cluster of receiving polygons. Since the largest subset needed for any particular cluster is much smaller than the total size of the environment, these subset computations can be performed in much less memory than can classical or hierarchical radiosity. The computation is then ordered for further efficiency. Careful ordering of ene...

Abstract – Computer augmented reality (CAR) is a rapidly emerging field which enables users to mix real and virtual worlds. Our goal is to provide interactive tools to perform common illumination, i.e., light interactions between real and virtual objects, including shadows and relighting (real and virtual light source modification). In particular, we concentrate on virtually modifying real light source intensities and inserting virtual lights and objects into a real scene; such changes can be very useful for virtual lighting design and prototyping. To achieve this, we present a three-step method. We first reconstruct a simplified representation of real scene geometry using semi-automatic vision-based techniques. With the simplified geometry, and by adapting recent hierarchical radiosity algorithms, we construct an approximation of real scene light exchanges. We next perform a preprocessing step, based on the radiosity system, to create unoccluded illumination textures. These replace the original scene textures which contained real light effects such as shadows from real lights. This texture is then modulated by a ratio of the radiosity (which can be changed) over a display factor which corresponds to the radiosity for which occlusion has been ignored. Since our goal is to achieve a convincing relighting effect, rather than an accurate solution, we present a heuristic correction process which results in visually plausible renderings. Finally, we perform an interactive process to compute new illumination with modified real and virtual light intensities. Our results show that we are able to virtually relight real scenes interactively, including modifications and additions of virtual light sources and objects. Index terms – Hierarchical radiosity, global illumination, interactivity, computer augmented reality, common illumination, virtual relighting. 1

Abstract: The advent of computer augmented reality (CAR), in which computer generated objects mix with real video images, has resulted in many interesting new application domains. Providing common illumination between the real and synthetic objects can be very beneficial, since the additional visual cues (shadows, interreflections etc.) are critical to seamless real-synthetic world integration. Building on recent advances in computer graphics and computer vision, we present a new framework to resolving this problem. We address three specific aspects of the common illumination problem for CAR: (a) simplification of camera calibration and modeling of the real scene; (b) efficient update of illumination for moving CG objects and (c) efficient rendering of the merged world. A first working system is presented for a limited sub-problem: a static real scene and camera with moving CG objects. Novel advances in computer vision are used for camera calibration and user-friendly modeling of the real scene, a recent interactive radiosity update algorithm is adapted to provide fast illumination update and finally textured polygons are used for display. This approach allows interactive update rates on mid-range graphics workstations. Our new framework will hopefully lead to CAR systems with interactive common illumination without restrictions on the movement of real or synthetic objects, lights and cameras. 1

In this paper we introduce a new approach to controlling error in hierarchical clustering algorithms for radiosity. The new method ensures that just enough work is done to meet the user's quality criteria. To this end the importance of traditionally ignored visibility error is identified, and the concept of features is introduced as a way to evaluate the quality of an image. A methodology to evaluate error based on features is presented, which leads to the development of a multi-resolution visibility algorithm. An algorithm to construct a suitable hierarchy for clustering and multi-resolution visibility is also proposed. Results of the implementation show that the multiresolution approach has the potential of providing significant computational savings depending on the choice of feature size the user is interested in. They also illustrate the relevance of the featurebased error analysis. The proposed algorithms are well suited to the development of interactive lighting simulation syste...

Analytic visibility algorithms, for example methods which compute a subdivided mesh to represent shadows, are notoriously unrobust and hard to use in practice. We present a new method based on a generalized definition of extremal stabbing lines, which are the extremities of shadow boundaries. We treat scenes containing multiple edges or vertices in degenerate configurations, (e.g., collinear or coplanar). We introduce a robust ɛ method to determine whether each generalized extremal stabbing line is blocked, or is touched by these scene elements, and thus added to the line's generators. We develop robust blocker predicates for polygons which are smaller than ɛ. For larger ɛ values, small shadow features merge and eventually disappear. We can thus robustly connect generalized extremal stabbing lines in degenerate scenes to form shadow boundaries. We show that our approach is consistent, and that shadow boundary connectivity is preserved when features merge. We have implemented our algorithm, and show that we can robustly compute analytic shadow boundaries to the precision of our chosen ɛ threshold for non-trivial models, containing numerous degeneracies.

Introduction Lighting design is often tedious due to the required physical manipulation of real light sources and objects. As an alternative, we present an interactive system [1] to virtually modify the lighting and geometry of scenes with both real and synthetic objects, including mixed real/virtual lighting and shadows. 2. Pre-process In our method, real scene geometry is first approximately reconstructed from photographs. Additional images are taken from a single viewpoint with a real light in different positions to estimate reflectance. A filtering process is used to compensate for inaccuracies, and per image reflectances are averaged to generate an approximate diffuse reflectance image for the given viewpoint, removing shadows in the process. An example of extracted reflectance is given in Fig. 1(b). Other approaches could be used [2] for reflectance extraction. This reflectance estimate is used to initialise a global illumination hierarchical radiosity system, representing rea