Daniel R. Baum, Stephen Mann, Kevin P. Smith, and James M. Winget. Making Radiosity Usable: Automatic Preprocessing and Meshing Techniques for the Generation of Accurate Radiosity Solutions. Computer Graphics #ACM SIGGRAPH '91 Proceedings#, 25#4#:51#60, July 1991.  Home/Search   Document Not in Database   Summary   Related Articles   Check

....about the illumination is gained, adaptive subdivision schemes are used to refine regions of high radiosity gradients [9] The quality of the resulting images is heavily dependent on the size and shape of the initial mesh. This dependence has been recently discussed in the radiosity literature [10, 11]: shadows falling between mesh vertices can be entirely missed; shadow leaks and light leaks can occur; objects can appear to float in mid air; shadow areas can be expanded, reduced, or distorted; and shadow boundaries can appear jagged or excessively blurry. Furthermore, the traditional ....

....number of interactions between elements by an order of magnitude. Elements are automatically and adaptively refined by the algorithm, according to a user specified error bound. Thus, in addition to drastically reducing computation times, the algorithm also provides automatic meshing. Baum et al. [10] describe a series of clever techniques designed to preprocess an input model into a mesh that meets certain geometrical and topological requirements needed for computing accurate solutions. However, user intervention is not entirely eliminated, since the initial patch size must still be ....

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D. R. Baum, S. Mann, K. P. Smith, and J. M. Winget. "Making Radiosity Usable: Automatic Preprocessing and Meshing Techniques for the Generation of Accurate Radiosity Solutions," Computer Graphics, 25(4), July 1991, pp. 51--60.

....al. 5] designed a method for discontinuity meshing and multi wavelets. In effect, they are doing multi wavelets computations over a non square domain. However, their algorithm requires several expensive computations of push pull coefficients. Our algorithm avoids these computations. Baum et al. [1] designed a method for radiosity computations with arbitrary planar polygons, including polygons with holes. Their method ensures that the triangles produced are well shaped, and suited for radiosity computations. Since it is designed for non hierarchical radiosity, it is done in a preliminary ....

D. R. Baum, S. Mann, K. P. Smith, and J. M. Winget. Making Radiosity Usable: Automatic Preprocessing and Meshing Techniques for the Generation of Accurate Radiosity Solutions. Computer Graphics (ACM SIGGRAPH '91 Proceedings), 25(4):51--60, July 1991.

....q) level ; while (level maxLevel) Figure 2: Structure of an Adaptive Subdivision algorithm 1 There are several ways to subdivide a patch. Usually, a quadrilateral patch is subdivided into 4 subpatches with equal area while a triangular patch is subdivided into 2 or 4 subpatches [1]. boolean refineOracle( Patch p, float thresh) maxGrad = maximum intensity gradient over p if ( maxGrad thresh ) return true; else return false; Figure 3: Structure of a re nement oracle The function refineOracle 2 which is shown in Figure 3 plays a key role in this algorithm. ....

Daniel R. Baum, S. Mann, K. P. Smith, and James M. Winget. Making Radiosity Usable: Automatic Preprocessing and Meshing Techniques for the Generation of Accurate Radiosity Solutions. Computer Graphics (SIGGRAPH Proceedings), Volume 25(No. 4):pages 51-60, July 1991.

....n e On( Ok k log ( 2 nnlog ( O 1 ( Chapter 2. Previous Work on the Radiosity Problem 48 for its subelements. Also, quadtree meshes can feature T vertices, which lead to interpolation problems when rendering, as in Figure 11. This can be corrected by balancing and anchoring the mesh [Baum91]. An example of a quad tree mesh, and its anchored equivalent, is shown in Figure 12. Figure 11: Shading discontinuities at a T vertex. Figure 12: A quad tree mesh. Left, the original mesh. Right, the mesh after anchoring T vertices to eliminate illumination discontinuities. 2.4. Discussion ....

Daniel R. Baum, Stephen Mann, Kevin P. Smith, and James M. Winget. Making radiosity usable: Automatic preprocessing and meshing techniques for the generation of accurate radiosity solutions. Computer Graphics (SIGGRAPH '91 Proceedings), 25(4):51--60, July 1991.

....in the environment [55] Such algorithms require a correct representation of the boundary of the obstacles so that they can effectively construct the free space. Similarly, algorithms for lighting simulation process meshes constructed on the boundaries of the objects being lit or analysed [15]. If the boundaries have cracks, the mesh is malformed, causing errors and artifacts like spurious shadows in the result. Bad meshes can also produce errors in finite element analysis. Further, basic CAD CAM operations like computing the mass or volume of an object, solid modelling techniques ....

.... nearby vertices, where close and nearby are defined in terms of a pre specified tolerance. Some boundary based methods assume that either all the input triangles are consistently oriented or that the orientation of a triangle can be determined from the order of the vertices on its boundary [15, 21]. Such an assumption is often invalid since many data sets contain inconsistently oriented triangles. Other algorithms require (a lot of) user intervention [41, 61] are inherently 16 two dimensional [60, 63] or are limited to removing parts of zero volume (like internal walls) from CAD models ....

[Article contains additional citation context not shown here]

D. R. Baum, S. Mann, K. P. Smith, and J. M. Winget, Making radiosity usable: Automatic preprocessing and meshing techniques for the generation of accurate radiosity solutions, Proc. SIGGRAPH 91, Comput. Graph., Vol. 25, ACM SIGGRAPH, 1991, pp. 51--60.

....sometimes give lesser simplification than otherwise, it does have the advantage of eliminating the expensive floating point run time checksentirely. The basic idea behind merge tree dependencies has a strong resemblance to creating balanced subdivisions of quad trees as presented by Baum et al. in [2] where only a gradual change is permitted from regions of high simplifications to low simplifications. Details of how these merge tree dependencies are used during run time are giveninSection5.1. 5 Real Time Triangulation Once the merge tree with dependencies has been constructed offline it is ....

D.R.Baum,MannS.,SmithK.P.,andWingetJ.M. Making radiosity usable: Automatic preprocessing and meshing techniques for the generation of accurate radiosity solutions. Computer Graphics: Proceedings of SIGGRAPH'91, 25, No. 4:51--60, 1991.

....solid regions and then generate a correct triangulation enclosing the solid regions. Turk and Levoy [23] address the related issue of joining two polygonal meshes separated by a small 4 distance by clipping one with the other. Bhn and Wozny [24] fill cracks by using local techniques. Baum et al. [25] handle the problem of cracks in meshes by grouping together vertices that are closer than a given value #. None of these methods can be easily generalized to be able to handle genus simplifications, whereas our approach can naturally correct cracks as well as generate genus reducing ....

D. R. Baum, Mann S., Smith K. P., and Winget J. M., "Making radiosity usable: Automatic preprocessing and meshing techniques for the generation of accurate radiosity solutions," Computer Graphics: Proceedings of SIGGRAPH'91, vol. 25, No. 4, pp. 51--60, 1991.

....of the environment during the course of the solution. The initial work in adaptive subdivision is by Cohen et al. 3] In this work, they propose a subdivision method called sub structuring with hierarchical subdivision of the input surfaces into subsurfaces, patches and elements. Baum et al. [4] state the ultimate constraints required by the radiosity method and propose automatic subdivision method. Campbell and Fussell [5] present the subdivision for elimination of light leakage. Hanrahan et al. 6] propose a hierarchical representation of the environment. In their algorithm, the ....

D. R. Baum, S. Mann, K. P. Smith, and J. M. Winget, Making radiosity usable: automatic preprocessing and meshing techniques for the Generation of Accurate Radiosity Solutions. In Computer Graphics (Proceedings of SIGGRAPH'91), 25(4), 51--60 (1991).

....sometimes give lesser simplification than otherwise, it does have the advantage of eliminating the expensive floating point run time checks entirely. The basic idea behind merge tree dependencies has a strong resemblance to creating balanced subdivisions of quad trees as presented by Baum et al. in [3] where only a gradual change is permitted from regions of high simplifications to low simplifications. Details of how these merge tree dependencies are used during run time are given in Section 5.1. The pseudocode outlining the data structure for a merge tree node is given in Figure 7. The ....

D. R. Baum, Mann S., Smith K. P., and Winget J. M. Making radiosity usable: Automatic preprocessing and meshing techniques for the generation of accurate radiosity solutions. Computer Graphics: Proceedings of SIGGRAPH'91, 25, No. 4:51--60, 1991.

....and photographs of Chapter 7, this works well. 6.4.4 Additional Refinement After subdivision on shadow boundaries and across areas of high contrast, no element will have significant intensity contrast. However, rendering issues may generate a need for more mesh refinement. As discussed in [BMSW91] some meshes are better suited than others for hardware assisted Gouraud interpolation. Elements that have large aspect ratios can lead to shading anomalies. Also, when the tree representing element subdivision (in our case, the eBSP tree) becomes unbalanced, other artifacts may result. These ....

Daniel R. Baum, Stephen Mann, Kevin P. Smith, and James R. Winget. Making radiosity usable: Automatic preprocessing and meshing techniques for the generation of accurate radiosity solutions. Computer Graphics, 25(4):51--60, July 1991.

....to be rectangular, which simplifies mesh refinement and the interpolation of intensities across mesh elements. Several artifacts results from this topology: light leaks between illuminated and shadowed vertices, objects that appear to float in the air, and jagged shadow boundaries. Baum et al. [2] preprocess a polygonal scene model into a mesh meeting several topological requirements needed for computing accurate radiosity solutions. This alleviates light leaks, but since the mesh consists of triangles and quadrilaterals that may only be subdivided in a restricted manner, much subdivision ....

....and photographs of Section 5, this works well. 4.4.5 Additional Refinement After subdivision on shadow boundaries and across areas of high contrast, no element will have significant intensity contrast. However, rendering issues may generate a need for more mesh refinement. As discussed in [2], some meshes are better suited than others for hardware assisted Gouraud interpolation. Elements that have large aspect ratios can lead to shading anomalies. Also, when the tree representing element subdivision (in our case, the eBSP tree) becomes unbalanced, other artifacts may result. These ....

Daniel R. Baum, Stephen Mann, Kevin P. Smith, and James R. Winget. Making radiosity usable: Automatic preprocessing and meshing techniques for the generation of accurate radiosity solutions. Computer Graphics, 25(4):51--60, July 1991.

....of Q i x;y s four sub quads. A quad is triangulated before being rendered. If the quad shares an edge with finer resolution quads, that edge must be split and the quad s triangulation must incorporate the splitting vertices. This is commonly known as anchoring (see, for example, Baum et al. [19]) 4 Visibility of a Single Point This section and the next describe the hierarchical visibility technique and its application to the terrain rendering algorithm of Section 3. Consider a single terrain point p = x; y; z(x; y) The horizon at p is the boundary between the visible sky and the ....

Daniel R. Baum, Stephen Mann, Kevin P. Smith, and James M. Winget, "Making radiosity usable: Automatic preprocessing and meshing techniques for the generation of accurate radiosity solutions", in Computer Graphics (SIGGRAPH '91 Proceedings), Thomas W. Sederberg, Ed., July 1991, vol. 25, pp. 51--60.

....disadvantage of this approach is that it introduces error by replacing an accurate radiosity sample with an interpolated value. The second approach triangulates the large element that neighbors the T vertex so that all the new triangles share the radiosity value at the point of the T vertex [2]. This approach does not introduce error in the computed solution, but it can produce triangles with poor aspect ratios. Restricted quadtrees are generally used to minimize this problem. In a restricted, or balanced, quadtree, two elements or leaves are allowed to differ by at most one level of ....

BAUM, Daniel; MANN, Stephen; SMITH, Kevin; and WINGET, James. Making Radiosity Usable: AutomaticPreprocessing and Meshing Techniques for the Generation of Accurate Radiosity Solutions. Computer Graphics, v. 25, no. 4, July 1991, pp. 51-60.

....tessellations of the same boundary curve. The presence of these errors can complicate, and even preclude, application of algorithms that assume manifold properties. For example, cracks or degenerate geometry can result in leaking of light and create artifacts in a radiosity solution. Baum et al. [9] catalog some common types of errors and propose rules to avoid them. Other algorithms like visibility computation, constructive solid geometry, or collision detection, which require inside outside classification of points with respect to a model, also fail due to errors in the model. For example, ....

D. Baum, S. Mann, K. Smith, and J. Winget. Making radiosity usable: Automatic preprocessing and meshing techniques for the generation of accurate radiosity solutions. ACM Computer Graphics, 25(4):51--60, 1991. (SIGGRAPH Proceedings).

....visible through a portal sequence (i.e. in each other s antipenumbrae) can interact directly by exchanging luminous energy. Knowing a light source s antipenumbra would also be useful in the polygonal subdivision that shadowing and global illumination algorithms employ to model shadow boundaries [3, 4, 12, 13, 21]. Finally, the algorithm is of theoretical interest for two reasons. First, for the class of input described here, the algorithm computes strong (antiumbral) and weak (antipenumbral) polygon visibility [17] with respect to a polygon (area light source) in 3D. Second, again for this input ....

Daniel R. Baum, StephenMann, Kevin P. Smith, and JamesM. Winget. Making radiosity usable: Automatic preprocessing and meshing techniques for the generation of accurate radiosity solutions. Computer Graphics (Proc. SIGGRAPH '91), 25(4):51--60, 1991.

....be known a priori. This is a situation that is commonly encountered in solving field equations and the usual approach to dealing with it is to adapt the discretization dynamically in response to the developing solution. This approach has been applied to radiosity algorithms with great success [13, 21]. Unfortunately even after the discretization has been adapted to resolution required for a solution, there is no guarantee that this resolution will be appropriate for constructing an image. This remains an unsolved problem. 2 Monte Carlo methods Monte Carlo methods estimate the value of ....

Baum, D., Mann, S., Smith, K. & Winget, J. "Making radiosity usable: automatic preprocessing and meshing techniques for the generation of accurate radiosity solutions." Computer Graphics 25:4 (1991) pp. 5160.

....(or luminance) Conceptually, for every pair of polygons, A and B, a form factor is computed which measures the fraction of the energy leaving polygon A that arrives at polygon B. This approach yields a set of simultaneous equations which are solved to obtain the radiance for each polygon. See [7, 15, 28, 29, 30, 40] for more information. The advantage of radiosity methods for interactive visualization is that a global radiosity solution can be precomputed, i.e. the solution does not depend on a particular observer viewpoint (see Figure 1.7) Therefore, a radiosity computation can be performed for an entire ....

Baum, Daniel, R., Stephen Mann, Kevin P. Smith, and James M. Winget. Making Radiosity Usable: Automatic Preprocessing and Meshing Techniques for the Generation of Accurate Radiosity. Computer Graphics (Proc. SIGGRAPH '91), 25, 4 (August 1991), 51-60.

....(iii) visible interaction. Figure 12: Reclassification of child interactions after subdivision. The linespace algorithms guarantee conservative visibility, in that blockers are only discarded from interactions if they are definitely known to be disjoint. Existing algorithms use point sampling [2, 6, 11, 16] or point to area visibility [3, 4] techniques and therefore do not guarantee correct inter area visibility determination. In contrast, we establish exact visibility information where possible, and adaptively subdivide until the uncertainty of visibility estimation in the remaining cases is so ....

Baum, D. R., Mann, S., Smith, K. P., and Winget, J. M. Making Radiosity Usable: Automatic Preprocessing and Meshing Techniques for the Generation of Accurate Radiosity Solutions. Computer Graphics (Proc. SIGGRAPH '91) 25, 4 (1991), 51\Gamma60.

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Daniel R. Baum, Stephen Mann, Kevin P. Smith, and James M. Winget. Making Radiosity Usable: Automatic Preprocessing and Meshing Techniques for the Generation of Accurate Radiosity Solutions. Computer Graphics #ACM SIGGRAPH '91 Proceedings#, 25#4#:51#60, July 1991.

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D.R.Baum, S.Mann, K.P.Smith and J.M.Winget, "Making Radiosity Usable: Automatic Preprocessing and Meshing Techniques for the Generation of Accurate Radiosity Solutions," Computer Graphics, 25(4), 1991, pp.51--60.

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D. R. Baum, Mann S., Smith K. P., and Winget J. M. Making radiosity usable: Automatic preprocessing and meshing techniques for the generation of accurate radiosity solutions. Computer Graphics: Proceedings of SIGGRAPH'91, 25, No. 4:51--60, 1991.

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Daniel R. Baum, Stephen Mann, Kevin P. Smith, and James M. Winget. Making radiosity usable: Automatic preprocessing and meshing techniques for the generation of accurate radiosity solutions. In Thomas W. Sederberg, editor, Computer Graphics (SIGGRAPH '91 Proceedings), volume 25, pages 51--60, July 1991.

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Daniel R. Baum, Stephen Mann, Kevin P. Smith, and James M. Winget. Making radiosity usable: Automatic preprocessing and meshing techniques for the generation of accurate radiosity solutions. Computer Graphics (SIGGRAPH '91 Proceedings), July 1991.

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D. R. Baum, S. Mann and J. M. Winget, "Making Radiosity Usable: Automatic Preprocessing and Meshing Techniques for the Generation of Accurate Radiosity Solutions". ACM Computer Graphics, Proc. SIGGRAPH '91, pp. 51--60, 1991.

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D.R.Baum, S.Mann, K.P.Smith and J.M.Winget, "Making Radiosity Usable: Automatic Preprocessing and Meshing Techniques for the Generation of Accurate Radiosity Solutions," Computer Graphics, 25(4), 1991, pp.51--60.

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