Gregory J. Ward and Paul Heckbert. Irradiance Gradients. Third Eurographics Workshop on Rendering, pages 85--98, May 1992.  Home/Search   Document Not in Database   Summary   Related Articles   Check

....in such models and cannot always be reconstructed, and intersecting polygons are often present in the models. All of these properties can lead to robustness problems for geometric algorithms. 1. 1 Motivation To create shadow meshes, in particular for soft shadows, discontinuity meshing approaches [13, 6, 16] intersect shadow boundary surfaces, or swaths, with scene geometry. This approach is inevitably unrobust for large and degenerate scenes, since numerical problems quickly lead to loss of connectivity in the shadow mesh, or result in geometrical errors due to small features. We can observe ....

....methods have been developed, for example the methods of Campbell and Fussell [3] or Chin and Feiner [4] based on BSP trees, which also run into robustness or memory problems due to the geometric operations and data structures involved. Discontinuity meshing approaches were introduced by Heckbert [13] and Lischinski et al. 16] These methods compute shadow discontinuity surfaces (line swaths) by intersecting them with the scene, with the resulting robustness problems previously discussed in Sect. 1.1. The ideas developed in the original aspect graph vision literature [14, 11] and introduced ....

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P. Heckbert. Discontinuity meshing for radiosity. Proc. Third Eurographics Workshop on Rendering, Bristol, pages 203--226, May 1992.

....assumes a constant radiosity distribution across each surface patch and finite element, then the values are interpolated across each mesh element. Meshing surfaces without considering the shadow structure can lead to inaccurate solutions and shadow leaks . The discontinuity meshing approach [17, 25, 30] was developed to avoid these problems. For each source, a discontinuity mesh is created on the scenes surfaces (receivers) The mesh includes all lines where the illumination function has discontinuities, including the effects of boundaries of multiple occluders. Meshing concerns have been a ....

Paul Heckbert. Discontinuity Meshing for Radiosity. Third Eurographics Workshop on Rendering, pages 203--226, May 1992.

....for faster image synthesis. This includes for example methods for finding shadows [Chin89, Telle92, Drett94, Stewa94, Hart99] discontinuity meshing [Heckb92, Lisch93] subdividing image space according to object and shadow boundaries [Pighi97] and adaptive interpolation of indirect light [Ward92]. currently at iMagis GRAVIR INRIA, Sophia Antipolis, France The Directional Coherence Maps of Guo [Guo98] provide an interpolation method even for finer details of the solution. This method tries to find the main orientation of shading details (a shadow or a glossy highlight) and object ....

Gregory J. Ward and Paul Heckbert. Irradiance gradients. Third Eurographics Workshop on Rendering, pages 85--98, May 1992.

....method as a means of constructing a more accurate mesh that will include all these edges. The first study on DM was presented by Heckbert [14] for a 2 D domain by considering every possible interaction between the edges and vertices in the scene and was later extended to a 3 D environment [13]. Concurrently a different 3 D algorithm was proposed by Lishinski et al. [15] which was subsequently combined with Hierarchical Radiosity [16] All of these methods accounted only for EV edges. EEE surfaces were partly treated by Teller [22] in a related computation where the visible region of a ....

P. Heckbert. Discontinuity meshing for radiosity. Third Eurographics Workshop on Rendering, pages 203--226, May 1992.

....tightest boundary. V Figure 1: A region with the constant visibility. The discontinuity lines and the visibility were intensively studied not only in 2D [21, 1, 6, 16] but mostly in 3D computer graphics [11] Main areas where we can meet them are computer vision [7, 8] and global illumination [10, 3, 20, 4]. Similar structure as we use was utilised in 3D in order to maintain the view from a viewpoint moving along a straight line [13] We review nowadays algorithms for dynamic visibility in the plane in the following section. In section 3, we briefly describe data structures for storing the ....

P. Heckbert. Discontinuity meshing for radiosity. Third Eurographics Workshop on Rendering, pages 203--226, May 1992.

....The introduction of partial results due to algorithmic dependencies Even a single stage of a problem may contain a number of distinct substages which must first be completed before the next substage can proceed. An example of this is the 50 use of an iterative solver, such as the Jacobi method [22, 35], to solve a set of simultaneous equations. An iterative method starts with an approximate solution and uses it in a recurrence formula to provide another approximate solution. By repeatedly applying this process a sequence of solutions is obtained which, under suitable conditions, converges ....

....algorithm is not possible. Parallel Computing, 3:259 260, 1986. 20] H. P. Flatt and K. Kennedy. Performance of parallel processors. Parallel Computing, 12:1 20, 1989. 21] M. J. Flynn. Some computer organisations and their effectiveness. IEEE Transactions on Computers, 21(9) 948 960, 1972. [22] C. F. Gerald and P. O. Wheatley. Applied numerical analysis. World Student Series. Addison Wesley, Reading, MA, 5 th edition, 1994. 23] S. A. Green and D. J. Paddon. A non shared memory multiprocessor architecture for large database problems. In M. Cosnard, M. H. Barton, and M. Vanneschi, ....

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Gregory J. Ward and Paul S. Heckbert, Irradiance Gradients. Third Eurographics Workshop on Rendering. 3 (1992).

....A disadvantage of these approaches is that the meshes are usually very regular which limits their ability of adaptation to the behavior of the radiance function, and thus their efficiency. An example is discontinuitymeshing versus regular meshing by quadtree subdivision for radiosity calculation [14, 19]. The cell boundaries of a discontinuity mesh are chosen so that they follow geometrically the discontinuities of different order of the radiosity function, while locations of the cell boundaries of a quadtree are fixed. Discontinuities are approximated by the quadtree by a large number of small ....

P.S. Heckbert, Discontinuity Meshing for Radiosity, Third Eurographics Workshop on Rendering, 1992, 203--216 57

....in two manners. The first approach is variable geometry, that is, cell boundaries follow shape characteristics of the function, for example discontinuities of different order. In radiosity calculation, adaptive meshes have been used for so called discontinuity meshing of the radiosity function [8, 12]. The second approach is hierarchical meshing. A mesh hierarchy is obtained by a cell subdivision scheme by which cells are replaced with subcells, possibly iteratively, at locations where the given bound of approximation of the true function requires that. This means that cell density varies ....

P.S. Heckbert, Discontinuity Meshing for Radiosity, Third Eurographics Workshop on Rendering, 1992, 203--216

....assumes a constant radiosity distribution across each surface patch and finite element, then the values are interpolated across each mesh element. Meshing surfaces without considering the shadow structure can lead to inaccurate solutions and shadow leaks . The discontinuity meshing approach [17, 25, 30] was developed to avoid these problems. For each source, a discontinuity mesh is created on the scenes surfaces (receivers) The mesh includes all lines where the illumination function has discontinuities, including the effects of boundaries of multiple occluders. Meshing concerns have been a ....

Paul Heckbert. Discontinuity Meshing for Radiosity. Third Eurographics Workshop on Rendering, pages 203--226, May 1992.

....to the limits of umbra and penumbra. By choosing certain of these boundaries and using them to guide the (irregular) mesh structure, disINRIA Fast and Accurate Hierarchical Radiosity. 5 continuity meshing lighting algorithms have been introduced resulting in more visually accurate images (e.g. [Hec92, LTG92]) In the vision literature, visual events have been extensively studied [PD90, GCS91] The aspect graph structure completely encodes all visibility events in a scene. The determination of the visible part of an area light source in computer graphics is exactly the calculation of the aspect of ....

....architectural scenes [TH93] accurately characterises links as visible, invisible or partially visible. This triage guides subdivision, allowing finer subdivision in partially illuminated regions. Discontinuity meshing clearly improves the visual quality of images 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 ....

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Paul Heckbert. Discontinuity meshing for radiosity. Third Eurographics Workshop on Rendering, pages 203--226, May 1992.

....lighting, all of its algorithms are tailored to that need and not necessarily geared towards easy parallelization. It is mainly based on a distribution ray tracer with various additional data structures that hold lighting information which is gathered using a unique irradiance sampling approach [14]. Although it was not conceived as a general graphics framework, Radiance gives an indication of the type of algorithms that appear in graphics applications, and which must be dealt with in a viable parallelization strategy. 2.2 Pixar RenderMan The RenderMan interface is a high level scene ....

Gregory J. Ward and Paul Heckbert. Irradiance gradients. Third Eurographics Workshop on Rendering, pages 85--98, May 1992.

....touches a receiver, the illumination function from an extended source is continuous, and exhibits discontinuities only in its derivatives. Techniques for computing discontinuity meshes operate by considering all possible visual events and inserting critical lines in an explicit mesh structure [11, 15], which makes them both quite expensive to use and subject to robustness issues. However, they can provide exact visibility [8] and produce images of the highest quality. Interactive shadow generation Shadows can be generated while displaying the scene, using one or more extra rendering passes. ....

Paul Heckbert. Discontinuity meshing for radiosity. Third Eurographics Workshop on Rendering, pages 203--226, May 1992.

....function If we know the radiosity values and the gradient at our sample points, we can then reconstruct the radiosity function as, e.g. a bicubic spline. Salesin et al. 10] and Bastos et al. 3] proposed such methods for reconstruction of radiosity using estimates of gradient. Ward and Heckbert [12] computed irradiance gradients to interpolate irradiance on receiving surfaces. Refinement criterion Many radiosity algorithms assume a constant radiosity over patches. It may seem strange to compute the gradient of radiosity in that case, but in fact the information given by the gradient can ....

Ward, G. J., Heckbert, P. S.: Irradiance Gradients. Third Eurographics Workshop on Rendering (May 1992) 85--98

....CF92] using binary space partitioning trees. Campbell and Fussell [CF91] Lischinski, Tampieri, and Greenberg [LTG92] and others compute a subset of the shadow boundaries which includes the boundaries of the umbra and penumbra regions. The most complete algorithm to date is that of Heckbert [Hec92], which will be described later. The problem we address is closely related to the computation of aspect graphs, as studied in computer vision [GCS91] The aspect graph represents all possible views of a scene by partitioning the viewpoint space into regions such that the structure of the scene is ....

....of a discontinuity surface with one of the faces of the scene. For a given scene, the oe aspect graph consists of, for every polyhedron face of the scene, the arrangement of all discontinuity curves on that face. The problem is to compute the oe aspect graph for a given scene. Heckbert [Hec92] considers a slightly different problem, that of computing the aspect graph with respect to every polygon in the scene, rather than a single polygon oe. The algorithm generates all potential planar discontinuity surfaces, each being defined by an edge vertex pair in the scene. The algorithm ....

Paul Heckbert. Discontinuitymeshing for radiosity. Third Eurographics Workshop on Rendering, pages 203--215, May 1992.

....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 ....

....scene, a D1 discontinuity surface occurs in two situations: either (a) two segments are coplanar and the plane embedding them intersects the light source or (b) the plane embedding a face of the scene intersects the light source. Identifying D1 surfaces has been studied elsewhere [GM90, Hec92a, LTG92, DF94] and will not be treated here. A D1 surface is a bounded, infinite region of a plane. If two edges define the surface, the surface consists of those points x from which a ray can be drawn that intersects one edge, then the other edge, then the light source (in that order) without intersecting the ....

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P. Heckbert. Discontinuity meshing for radiosity. Third Eurographics Workshop on Rendering, pages 203--215, May 1992.

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Gregory J. Ward and Paul Heckbert. Irradiance Gradients. Third Eurographics Workshop on Rendering, pages 85--98, May 1992.

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Paul Heckbert. Discontinuity Meshing for Radiosity. Third Eurographics Workshop on Rendering, pages 203--226, May 1992.

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Gregory J. Ward and Paul Heckbert. Irradiance Gradients. Third Eurographics Workshop on Rendering, pages 85--98, May 1992.

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Paul Heckbert. Discontinuity Meshing for Radiosity. Third Eurographics Workshop on Rendering, pages 203--226, May 1992.

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Gregory J. Ward and Paul Heckbert. Irradiance gradients. Third Eurographics Workshop on Rendering, pages 85--98, May 1992.

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Gregory J. Ward and Paul Heckbert. Irradiance gradients. Third Eurographics Workshop on Rendering, pages 85--98, May 1992.

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Paul Heckbert. Discontinuity meshing for radiosity. Third Eurographics Workshop on Rendering, pages 203--226, May 1992.

No context found.

Gregory J. Ward and Paul Heckbert. Irradiance Gradients. Third Eurographics Workshop on Rendering, pages 85--98, May 1992.

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Gregory J. Ward and Paul Heckbert. Irradiance Gradients. Third Eurographics Workshop on Rendering, pages 85--98, May 1992.

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G. Ward / P. Heckbert, Irradiance Gradients, Proc. Third Eurographics Workshop on Rendering '92, pp. 85--98 c fl The Eurographics Association Kobbelt et al. / Radiosity Reconstruction with Subdivision Kobbelt et al.,

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