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Proceedings of the 19th annual conference on computer graphics and interactive techniques

作者： David Baraff Andrew Witkin Program of Computer Graphics Cornell University Ithaca NY School of Computer Science Carnegie Mellon University Pittsburgh PA

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Coping with friction for non-penetrating rigid body simulation 91

Coping with friction for non-penetrating rigid body simulati...

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18th Annual Conference on computer graphics and Interactive Techniques, SIGGRAPH 1991

作者： Baraff, David Program of Computer Graphics Cornell University IthacaNY14853 United States

ISBN: (纸本)0897914368

Algorithms and computational complexity measures for simulating the motion of contacting bodies with friction are presented. The bodies are restricted to be perfectly rigid bodies that contact at finitely many points. Contact forces between bodies must satisfy the Coulomb model of friction. A traditional principle of mechanics is that contact forces are impulsive if and only if non-impulsive contact forces are insufficient to maintain the non-penetration constraints between bodies. When friction is allowed, it is known that impulsive contact forces can be necessary even in the absence of collisions between bodies. This paper shows that computing contact forces according to this traditional principle is likely to require exponential time. An analysis of this result reveals that the principle for when impulses can occur is too restrictive, and a natural reformulation of the principle is proposed. Using the reformulated principle, an algorithm with expected polynomial time behavior for computing contact forces is presented. © 1991 ACM.

关键词： Friction

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A comprehensive physical model for light reflection 91

A comprehensive physical model for light reflection

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18th Annual Conference on computer graphics and Interactive Techniques, SIGGRAPH 1991

作者： He, XiaoD . Torrance, Kenneth E. Sillion, Francois X. Greenberg, Donald P. Program of Computer Graphics Cornell University IthacaNY14853 United States

ISBN: (纸本)0897914368

A new general reflectance model for computer graphics is presented . The model is based on physical optics and describes specular, directional diffuse, and uniform diffuse reflection by a surface. The reflected light pattern depends on wavelength , incidence angle, two surface roughness parameters, and surface refractive index. The formulation is self consistent in terms of polarization , surface roughness, masking/shadowing, and energy. The model applies to a wide range of materials and surface finishes and provides a smooth transition from diffuse-like to specular reflection as the wavelength and incidence angle are increased or the surface roughness is decreased. The model is analytic and suitable for computer graphics applications. Predicted reflectance distributions compare favorably with experiment. The model is applied to metallic, nonmetallic, and plastic materials , with smooth and rough surfaces. © 1991 ACM.

关键词： Surface roughness

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A global illumination solution for general reflectance distributions 91

A global illumination solution for general reflectance distr...

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18th Annual Conference on computer graphics and Interactive Techniques, SIGGRAPH 1991

作者： Sillion, Francois X. Arvo, James R. Westin, Stephen H. Greenberg, Donald P. Program of Computer Graphics Cornell University IthacaNY14853 United States

ISBN: (纸本)0897914368

A general light transfer simulation algorithm for environments composed of materials with arbitrary reflectance functions is presented. This algorithm removes the previous practical restriction to ideal specular and/or ideal diffuse environments, and supports complex physically based reflectance distributions. This is accomplished by extending previous two-pass ray-casting radiosity approaches to handle non-uniform intensity distributions, and resolving all possible energy transfers between sample points. An implementation is described based on a spherical harmonic decomposition for encoding both bidirectional reflectance distribution functions for materials, and directional intensity distributions for illuminated surfaces. © 1991 ACM.

关键词： Reflection

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Design and Simulation of Opera Lighting and Projection Effects 91

Design and Simulation of Opera Lighting and Projection Effec...

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18th Annual Conference on computer graphics and Interactive Techniques, SIGGRAPH 1991

作者： Dorsey, Julie O B. Sillion, Francois X. Greenberg, Donald P. Program of Computer Graphics Cornell University Ithaca New York14853 United States

ISBN: (纸本)0897914368

A major problem challenging opera designers is the inability to coordinate lighting, projection systems, and set designs in the preliminary planning phase. New computer graphics techniques, which provide the set and lighting designer [be opportunity to evaluate, test, and control opera designs prior to the construction of full scale systems are presented, These techniques-light source input. simulation of directional lighting, modeling of scenic projection systems, and full three-dimensional simulation-show the potential for the use of computer graphics in theater design, The light source input component consists of a program for assigning light source attributes with a set of theater lighting icons. This module allows a designer to specify light source characteristics in a way familiar to the discipline and to make preliminary evaluations of the lighting conditions. An extended progressive radiosity method is introduced to simulate the directional lighting characteristics which are specified by the input program. A new projection approach is presented to simulate the optical effects of scenic projectors. In addition, a solution to the distortion problem produced by angular projections is described. The above components are integrated to produce full threedimensional simulations of the global illumination effects in an opera scene. © 1991 ACM.

关键词： Light sources

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Unbiased sampling techniques for image synthesis 91

Unbiased sampling techniques for image synthesis

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18th Annual Conference on computer graphics and Interactive Techniques, SIGGRAPH 1991

作者： Kirk, David Arvo, James California Institute of Technology Computer Graphics 350-74 PasadenaCA91125 United States Program of Computer Graphics Cornell University IthacaNY14853 United States

ISBN: (纸本)0897914368

We examine a class of adaptive sampling techniques employed in image synthesis and show that those commonly used for efficient anti-aliasing are statistically biased. This bias is dependent upon the image function being sampled as well as the strategy for determining the number of samples to use. It is most prominent in areas of high contrast and is attributable to early stages of sampling systematically favoring one extreme or the other. If the expected outcome of the entire adaptive sampling algorithm is considered, we find that the bias of the early decisions is stiO present in the final estimator. We propose an alternative strategy for performing adaptive sampling that is unbiased but potentially more costly. We conclude that it may not always be practical to mitigate this source of bias, but as a source of error it should be considered when high accuracy and image fidelity are a central concern. © 1991 ACM.

关键词： Anti-aliasing

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Acceleration techniques for progressive refinement radiosity 90

Acceleration techniques for progressive refinement radiosity

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1990 Symposium on Interactive 3D graphics, I3D 1990

作者： Recker, Rodney J. George., David W. Greenberg, Donald P. Program of Computer Graphics Cornell University United States

ISBN: (纸本)0897913515

The progressive refinement radiosity method provides a means for computing the global illumination of an environment in time proportional to the size-of the environment. Additionally, the method supplies a sequence of solutions that monotonically converge to a high-quality result, allowing it to be used for interactive applications that deliver "near real-time' updates as the computation proceeds. This paper presents two methods for accelerating the radiosity method. First, the traditional hemi-cube algorithm is modified to accelerate the expensive form-factor calculation. Second, the radiosity method is parallelized across a coarsegrain network, and the efficiency of the parallel system is discussed. © 1990 ACM.

关键词： Coarse-grain parallelism Global illumination Item buffer Radiosity. progressive refinement

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An efficient method for volume rendering using perspective projection

An efficient method for volume rendering using perspective p...

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1990 Workshop on Volume Visualization, VVS 1990

作者： Novins, Kevin L. Sillion, Frangois X. Greenberg, Donald P. Program of Computer Graphics Cornell University IthacaNY14850 United States

ISBN: (纸本)0897914171

Use of the perspective projection adds important perceptual cues for image comprehension. However, it has not been widely used in volume rendering because of the lack of efficient computational algorithms and concern over the non uniform sampling rate imposed by perspective ray divergence. This paper introduces two new techniques to help make perspective projection more feasible in rendering volume data. First, a method is presented for efficient slice-by-slice processing of volume data, allowing high resolution data sets by eliminating typical memory constraints. Second, an adaptive "ray splitting" approach is described which ensures that the entire volume is sampled within user-specified limits. Additionally, we present results using distributed ray tracing to achieve depth of field effects. © 1990 ACM.

关键词： Ray tracing

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Effects of structural imperfections on constant-feedback-gain control of a spatial structure

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Computing Systems in Engineering 1990年第2-4期1卷 601-606页

作者： Aubert, B.H. Abel, J.F. Lu, J. Thorp, J.S. School of Civil and Environmental Engineering Program of Computer Graphics Cornell University Ithaca NY 14853 United States School of Electrical Engineering Cornell University Ithaca NY 14853 United States

The numerical sensitivity of a constant-feedback-gains controller to random structural imperfections is examined using the results of a series of finite element analyses. The basic finite element model, which uses linear beam-column elements, is a two-dimensional simplification of a large (10 m long) three-dimensional frame currently undergoing testing at cornell University. The cross-sectional properties, nodal coordinates, and masses of the models were randomly varied within four different ranges of maximum imperfection. Twenty transient dynamic analyses were run for each range of structural perturbation. Each analysis used a different random distribution of imperfections. The results of the finite element analyses show that the optimal control configuration, found by dynamic programming, exhibited unacceptable sensitivity to small perturbations of the structural model. A second, nearly optimal, control configuration was found to be more robust with respect to structural imperfections. © 1990.

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Too many cooks don't spoil the broth: light simulation on massively parallel computers

Too many cooks don't spoil the broth: light simulation on ma...

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Frontiers of Massively Parallel Computation

作者： P. Kochevar Program of Computer Graphics Cornell University USA

A computer graphics algorithm for simulating the propagation of light and its interaction with matter on a massively parallel computer is presented. This algorithm, called the tagged shooting method, is designed for a virtual machine containing a great number of simple communicating processors arrayed into a cubical three-dimensional lattice. Only nearest neighbor communication among processors is assumed, and there is no reliance on global shared memory. The algorithm is similar in spirit to the classical progressive refinement radiosity method designed for more conventional computers but is not an adaptation of that technique to massive parallelism. Instead, the new algorithm uses a discretization of the wave equation as a local rule for shuttling radiant energy values between processors that correspond to regions of space. A number of example images that were created with an implementation of the algorithm on a Connection Machine are depicted and critiqued.< >

关键词： Computational modeling Concurrent computing Design methodology Algorithm design and analysis computer graphics computer simulation Optical propagation Virtual machining Lattices Nearest neighbor searches

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