Exact radiosity reconstruction and shadow computation using vertex tracing (original) (raw)
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Eurographics Symposium on Rendering/Eurographics Workshop on Rendering Techniques, 2000
Methods for exact computation of irradiance and form factors associ- ated with polygonal objects have ultimately relied on a formula for a differential area to polygon form factor attributed to Lambert. This paper presents an alter- native, an analytical expression based on vertex behavior rather than the edges the polygon. Using this formulation, irradiance values in a scene consisting of
Fast and accurate hierarchical radiosity using global visibility
ACM Transactions on Graphics, 1999
Recent hierarchical global illumination algorithms permit the generation of images with a high degree of realism. Nonetheless, appropriate refinement of light transfers, high quality meshing and accurate visibility calculation can be challenging tasks. This is particularly true for scenes containing multiple light sources and scenes lit mainly by indirect light. We present solutions to these problems by extending a global visibility data structure, the Visibility Skeleton. This extension allows us to calculate exact point-to-polygon form-factors at vertices created by subdivision. The structure also provides visibility information for all light interactions, allowing intelligent refinement strategies. High-quality meshing is effected based on a perceptually-based ranking strategy which results in appropriate insertions of discontinuity curves into the meshes representing illumination. We introduce a hierarchy of triangulations which allows the generation of a hierarchical radiosity solution using accurate visibility and meshing. Results of our implementation show that our new algorithm produces high quality view-independent lighting solutions for direct illumination, for scenes with multiple lights and also scenes lit mainly by indirect illumination.
IEEE Computer Graphics and Applications, 1998
This paper present s a v olumetric representation for the global illumination within a space based on the radiometric quantity irradiance. We call this representation the irradiance volume. Although irradiance is traditionally computed only for surfaces, we extend its de nition to all points and directions in space. The irradiance volume supports the reconstruction of believable approximations to the illumination in situations that overwhelm traditional global illumination algorithms. A theoretical basis for the irradiance volume is discussed and the methods and issues involved with building the volume are described. The irradiance volume method shows good performance in several practical situations.
A density estimation technique for radiosity
2002
Radiosity computation on scenes including objects with a complex geometry, or with a large number of faces and meshes with very different sizes, is very complex. We present a new method (based on the Photon Maps method [7]) where density estimation on the tangent plane at each surface point is performed for irradiance computation by using photon paths (line segments traveled by a ray) instead of photon impacts. Therefore we improve the results for scenes containing small objects which receive only a few impacts. Also, geometry is completely decoupled from radiosity computation.
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ACM SIGGRAPH Computer Graphics, 1989
A new method for computing form-factors within a progressive radiosity approach is presented. Previously, the progressive radiosity approach has depended on the use of the hemi-cube algorithm to determine form-factors. However, sampling problems inherent in the hemi-cube algorithm limit its usefulness for complex images. A more robust approach is described in which ray tracing is used to perform the numerical integration of the form-factor equation. The approach is tailored to provide good, approximate results for a low number of rays, while still providing a smooth continuum of increasing accuracy for higher numbers of rays. Quantitative comparisons between analytically derived form-factors and ray traced form-factors are presented.
Accurate Visibility and Meshing Calculations for Hierarchical Radiosity
Eurographics, 1996
Precise quality control for hierarchical lighting simulations is still a hard problem, due in part to the difficulty of analysing the source of error and to the close interactions between different components of the algorithm. In this paper we attempt to address this issue by examining two of the most central components of these algorithms: visibility computation and the mesh. We first present an investigation tool in the form of a new hierarchical algorithm: this algorithmic extension encapsulates exact visibility information with respect to the light source in the form of the backprojection data structure, and allows the use of discontinuity meshes in the solution hierarchy. This tool permits us to study separately the effects of visibility and meshing error on image quality, computational expense as well as solution convergence. Initial experimental results are presented by comparing standard quadtree-based hierarchical radiosity with point-sampling visibility to the approaches incorporating backprojections, discontinuity meshes or both. Important components of the HR simulation algorithm Broadly speaking, two main categories of factors affecting simulation can be identified (following [1]): discretisation, concerning mainly issues of mesh construction and data structures, and computation which involves the aspects of the algorithm related to form-factor and visibility computation as well as refinement strategy and convergence. ยก iMAGIS is a joint research project
Computing exact shadow irradiance using splines
Proceedings of the 26th annual conference on Computer graphics and interactive techniques - SIGGRAPH '99, 1999
We present a solution to the general problem of characterizing shadows in scenes involving a uniform polygonal area emitter and a polygonal occluder in arbitrary position by manifesting shadow irradiance as a spline function. Studying generalized prism-like constructions generated by the emitter and the occluder in a fourdimensional (shadow) space reveals a simpler intrinsic structure of the shadow as compared to the more complicated 2D projection onto a receiver. A closed form expression for the spline shadow irradiance function is derived by twice applying Stokes' theorem to reduce an evaluation over a 4D domain to an explicit formula involving only 2D faces on the receiver, derived from the scene geometry. This leads to a straightforward computational algorithm and an interactive implementation. Moreover, this approach can be extended to scenes involving multiple emitters and occluders, as well as curved emitters, occluders, and receivers. Spline functions are constructed from these prism-like objects. We call them generalized polyhedral splines because they extend the classical polyhedral splines to include curved boundaries and a density function. The approach can be applied to more general problems such as some of those occurring in radiosity, and other related topics.
Improved explicit radiosity method for calculating non-Lambertian reflections
The Visual Computer, 1993
We present an improved radiosity method for accounting for non-Lambertian reflections. The method explicitly calculates the radiance distribution leaving each non-Lambertian surface. The method differs from previous explicit radiosity methods in two respects. First, non-Lambertian surfaces are discretized adaptively based on their effect on other surfaces, rather than on their own spatial radiance distribution. Second, the calculation of the radiance distribution for surfaces that are neither Lambertian nor mirror-like surfaces is made more efficient using the ideas of hemi-cube pixel groups and the reflectance hemisphere. The method is well suited to being used as the first pass in a multi-pass rendering method.
Real time volumetric shadows using polygonal light volumes
This paper presents a more efficient way of computing single scattering effects in homogeneous participating media for real-time purposes than the currently popular ray-marching based algorithms. These effects include halos around light sources, volumetric shadows and crepuscular rays. By displacing the vertices of a base mesh with the depths from a standard shadow map, we construct a polygonal mesh that encloses the volume of space that is directly illuminated by a light source. Using this volume we can calculate the airlight contribution for each pixel by considering only points along the eye-ray where shadow-transitions occur. Unlike previous ray-marching methods, our method calculates the exact airlight contribution, with respect to the shadow map resolution, at real time frame rates.