Filippo Tampieri. Discontinuity Meshing for Radiosity Image Synthesis. Ph.D. thesis, Cornell University, Ithaca, NY, 1993.  Home/Search   Document Not in Database   Summary   Related Articles   Check

....generated by lighting simulation [LTG92, Hec92, DF94] since the mesh used to represent illumination follows the actual shadow boundaries, instead of finely subdividing a quadtree which attempts to approximate the boundary. One problem is the extremely large number of discontinuities. Tampieri [Tam93] attempted to limit the number of discontinuity lines inserted, by sampling the illumination along the discontinuities and only inserting those with radiosity values differing more than an predefined threshold. In the context of progressive refinement radiosity, Stuerzlinger [Stu94] only inserted ....

....if the result will be just noticeable . Hedley et al. HWP97] in a similar spirit, use a tone mapping operator to determine whether a discontinuity should be inserted into a lighting simulation mesh. This is performed by sampling across the discontinuity (in a manner similar to that of Tampieri [Tam93]) but also orthogonally across the discontinuities. This results in an important reduction of discontinuities without loss of visual quality. 1.2 Paper Overview Previous algorithms surveyed above provide view independent lighting simulations which are acceptable for many situations. In ....

Filippo Tampieri. Discontinuity Meshing for Radiosity Image Synthesis. Ph.D. thesis, Cornell University, Ithaca, NY, 1993.

....Keywords: D1 discontinuity, discontinuity meshing, shadows, radiosity, global illumination. 1 Introduction For global illumination algorithms operating on polyhedral scenes illuminatedby an area light source, the discontinuity mesh is used to model accurately sharp changes in illumination [Hec91, Hec92a, LTG92, LTG93, Tam93]. The backprojection is a topological description of the boundary of the visible light source, as seen from some viewpoint. The discontinuity mesh is a set of maximal cells on the faces of the scene such that the backprojection is constant for all viewpoints within each cell. Adjacent cells on a ....

F. Tampieri. Discontinuity Meshing for Radiosity Image Synthesis. Ph.D. thesis, Cornell University, Ithaca, NY, 1993. available as Cornell technical report 93--1346.

....work a global solution is computed using a BSP tree. When a node is split, an appropriate discontinuity line is chosen. A local pass is subsequently used for display, during which analytic visibility (mainly for primary sources) is computed using an expensive polygon clipping operation (as in [10, 17]) The main difference with the method we present here is the fact that exact visibility was not taken into account during the solution process and thus the different factors (visibility, meshing) affecting error could not be isolated or analysed. Gatenby and Hewitt [5] also developed a ....

Filippo Tampieri. Discontinuity Meshing for Radiosity Image Synthesis. PhD thesis, Department of Computer Science, Cornell University, Ithaca, New York, 1993. PhD Thesis.

.... areas of high contrast such as shadow boundaries can often either be missed (due to bad placing of initial sample points) or cause mesh subdivision to proceed indefinitely, or at least down to a minimum element size which can leave noticeable jagged shadows (e.g. 1] Discontinuity Meshing [10, 12, 16] was proposed to rectify these problems by explicitly representing discontinuities in the radiance function. Discontinuities are located by tracing out critical surfaces formed by all combinations of source and occluder edges and vertices and the resulting constraint edges inserted into a ....

....exclusively with D 1 and D 2 discontinuities. We do not include D 0 discontinuities in our discussion as in general they can be determined without tracing out critical surfaces by using a simple geometry preprocess (e.g. 1] 2 Previous work 2. 1 Discontinuity ranking and culling Tampieri[16] first suggested the idea that many discontinuities have little or no visual effect and should be dropped. The need for a perceptual measure was recognised, but only a simple, radiometric measure was given: max x2c L ij (x) L old i (x) L ij (x) 1) where c is the discontinuity, L ij ....

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Filippo Tampieri. Discontinuity Meshing for Radiosity Image Synthesis. Ph.D. thesis, Technical Report, Ithaca, NY, 1993.

....sources are moved in step with the object. We propose a method which aims to allow interactive manipulation of objects, and will maintain the shadows cast by those objects. This is intended to complement the existing global methods for interactive radiosity [1,2,3,8] We use discontinuity meshing [6,7,11] as a basis, which was developed to represent discontinuous radiance functions accurately with few polygons. However, the computations required to locate the discontinuities and build the mesh are very large and are of the same order of magnitude as that of the radiosity calculations themselves. ....

....and edge edge events. We will only be concerned with vertex edge events in this paper. One approach to implementing discontinuity meshing for vertex edge events builds wedges between all pairs of source edges vertices and occluding vertices edges, and then traces these wedges out into the scene [7,11]. Figure 1 shows a source vertex and occluding edge, and traces a wedge out which intersects a surface. Figure 1 : Wedge tracing in discontinuity meshing Although there are two types of vertex edge event, corresponding to source vertex occluder edge (or VE) and source edge occluder vertex (or ....

Tampieri F. "Discontinuity Meshing for Radiosity Image Synthesis", PhD Thesis (Cornell), May

....in order to adequately redistribute the accumulated form factors. So, on the opposite to diffuse facets which always keep their quadtrees[7] we destroy them in the case of specular facets. Moreover, in this part, we also take care of penumbra zones detection using an Adaptative Meshing Technique[12]. 4.1.2 Subdivision of light sources First of all, we consider light sources. We subdivide them in triangles (when they are rectangular) and each triangle is itself subdivided in a quadtreelike fashion until the computation of the form factors attached to them, described below, becomes ....

Filippo Tampieri. Discontinuity Meshing for Radiosity Image Synthesis. Ph.D. thesis, Cornell University, Ithaca, NY, 1993.

....representation of the radiosity function, consistent representation across solution and display stages, as well as potentially faster convergence in certain solution techniques. Lischinski, Tampieri and Greenberg used quadratic triangular interpolants in [39] described in more detail by Tampieri [60]) Salesin, Lischinski and DeRose [49] used cubic reconstruction over triangular elements to represent radiance. To this end a Clough Tocher cubic polynomial was built over triangles, and shadow discontinuities were subsequently represented by relaxing constraints over shadow boundaries. ....

....Chapter 5 Structured Sampling for Scenes with Occlusion 5. 1 Reconstructing Illumination in the Penumbra The sampling and reconstruction of radiance within penumbral regions was first attempted by Campbell and Fussell in [9] and later by Lischinski et al. 38] described in detail by Tampieri in [60]) Campbell and Fussell recognised that the variation of illumination in the penumbra was complicated and difficult to predict. They thus used numerical optimisation techniques to determine the behaviour of radiance in regions of shadow. In the approach by Tampieri, and by Lischinski et al. the ....

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Tampieri Fillipo, "Discontinuity Meshing for Radiosity Image Synthesis," Ph.D. Thesis, Department of Computer Science, Cornell University, Ithaca, New York, 1993.

....was described by the authors [18] The meshing in this algorithm is automatic. Using analytical visibility and form factor computations followed by quadratic interpolation it has produced radiosity solutions of impressive visual accuracy. This algorithm was also shown to be numerically accurate [24]. However, this method is too expensive for computing converged solutions of complex environment and only offers limited user control in trading off speed for accuracy. The main reason for this is that all energy transfers are computed very accurately, regardless of their magnitude. 4 A COMBINED ....

....than planar. However, the resulting discontinuities always lie within penumbra regions, and never define the outer boundaries of a shadow. For these reasons, we excluded EEE events from our current implementation. We described the discontinuity location algorithm in a previous paper [18] Tampieri [24] provides a more detailed description of this algorithm. Heckbert [15] and Teller [25] describe alternative algorithms for locating discontinuities. Teller s algorithm is the only one capable of handling EEE events. 5 THE GLOBAL PASS In order to understand how the accuracy of HR can be improved, ....

Tampieri, Filippo. Discontinuity Meshing for Radiosity Image Synthesis, PhD dissertation, Cornell University, Ithaca, New York, May 1993.

....of approximation schemes that are of higher degree [31] 16] 34] A. Observed Properties of Irradiance Campbell and Fussell [3] observed that irradiance in a penumbral region can exhibit multiple minima and maxima. Numerical optimization was used to determine these critical points. Tampieri [29] and Lischinski et al. 22] segmented the penumbral domain by the mesh generated solely from visual events caused by planar discontinuity surfaces including a source edge or vertex. They then postulated that within each face or cell of this mesh the irradiance varies little. A subsequent adaptive ....

....3 Fig. 4. A singular vertex polygon. An example of a convex backprojection instance is shown in grey on the light source in Fig. 3(a) and a concave example is shown in Fig. 3(b) which are both simple. An example of a disconnected backprojection is shown in Fig. 3(c) Singularities. As noted in [29] and [22] irradiance along a surface is singular at points at which two surfaces touch. Thus at a vertex in the mesh joining faces of umbra, penumbra and light, the irradiance is multi valued and is defined as a limit depending on the direction from which the vertex is approached. A singular ....

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Filippo Tampieri. Discontinuity Meshing for Radiosity Image Synthesis. PhD thesis, Department of Computer Science, Cornell University, Ithaca, New York, 1993. PhD Thesis.

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Filippo Tampieri. Discontinuity Meshing for Radiosity Image Synthesis. Ph.D. thesis, Cornell University, Ithaca, NY, 1993.

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