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ASSESSING THE EFFECT OF SHAPE DISTORTION IN Q9 MEMBRANE ELEMENTS

computerS & STRUCTURES 1989年第5期33卷 1183-1190页

作者： SALMON, DC ABEL, JF Depart ment of Architecture Cornell University Ithaca NY 14853 U.S.A. School of Civil and Environmental Engineering Program of Computer Graphics Cornell University Ithaca NY 14853 U.S.A.

The Q9 membrane finite element is unable to experience arbitrary change of uniaxial curvature without the occurence of artificial membrane stains. The error which accumulates due to this inability can be significant when a large change of curvature is experienced by this element. This paper investigates the effect of element shape distortion on the accumulation of error in the Q9 membrane element, and presents two methods for evaluating shape distortion effects in problems with large changes of curvature: a series of ‘patch tests’, and single element tests.

关键词： Membranes

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A Hybrid Monte Carlo Method for Accurate and Efficient Subsurface Scattering

A Hybrid Monte Carlo Method for Accurate and Efficient Subsu...

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16th Eurographics Symposium on Rendering Techniques, EGSR 2005

作者： Li, Hongsong Pellacini, Fabio Torrance, Kenneth Program of Computer Graphics Rhodes Hall Cornell University IthacaNY14853 United States

ISBN: (纸本)3905673231

Subsurface scattering is a fundamental aspect of surface appearance responsible for the characteristic look of many materials. Monte Carlo path tracing techniques can be employed with high accuracy to simulate the scattering of light inside a translucent object, albeit at the cost of long computation times. In a seminal work, Jensen et al. [JMLH01] presented a more efficient technique to simulate subsurface scattering that, while producing accurate results for translucent, optically-thick, materials, exhibits artifacts for semi-transparent, optically-thin, ones, especially in regions of high-curvature. This paper presents a hybrid Monte Carlo technique capable of simulating a wide range of materials exhibiting subsurface scattering, from translucent to semi-transparent ones, with an accuracy comparable to Monte Carlo techniques but at a much lower computational cost. Our approach utilizes a Monte Carlo path tracing approach for the first several scattering events, in order to estimate the directional-diffuse component of subsurface scattering, and switches to a dipole diffusion approximation only when the path penetrates deeply enough into the surface. By combining the accuracy of Monte Carlo integration with the efficiency of the dipole diffusion approximation, our hybrid method produces results as accurate as full Monte Carlo simulations at a speed comparable to the Jensen et al. approximation, thus extending its usefulness to a much wider range of materials. © The Eurographics Association 2005.

关键词： Monte Carlo methods

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Jigsaw image mosaics 02

Jigsaw image mosaics

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ACM Transactions on graphics;Proceedings of ACM SIGGRAPH 2002

作者： Kim, Junhwan Pellacini, Fabio Dept. of Computer Science Cornell University Ithaca NY United States Program of Computer Graphics Cornell University Ithaca NY United States

ISBN: (纸本)9781581135213

This paper introduces a new kind of mosaic, called Jigsaw Image Mosaic (JIM), where image tiles of arbitrary shape are used to compose the final picture. The generation of a Jigsaw Image Mosaic is a solution to the following problem: given an arbitrarily-shaped container image and a set of arbitrarily-shaped image tiles, fill the container as compactly as possible with tiles of similar color to the container taken from the input set while optionally deforming them slightly to achieve a more visually-pleasing effect. We approach the problem by defining a mosaic as the tile configuration that minimizes a mosaicing energy function. We introduce a general energy-based framework for mosaicing problems that extends some of the existing algorithms such as Photomosaics and Simulated Decorative Mosaics. We also present a fast algorithm to solve the mosaicing problem at an acceptable computational cost. We demonstrate the use of our method by applying it to a wide range of container images and tiles.

关键词： Color computer graphics

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The irradiance Jacobian for partially occluded polyhedral sources 94

The irradiance Jacobian for partially occluded polyhedral so...

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21st Annual Conference on computer graphics and Interactive Techniques, SIGGRAPH 1994

作者： Arvo, James Program of Computer Graphics Cornell University 580 Engineering and Theory Center Building IthacaNY14853 United States

ISBN: (纸本)0897916670

The irradiance at a point on a surface due to a polyhedral source of uniform brightness is given by a well-known analytic formula. In this paper we derive the corresponding analytic expression for the irradiance Jacobian, the derivative of the vector representation of irradiance. Although the result is elementary for unoccluded sources, within penumbrae the irradiance Jacobianmust incorporate more information about blockers than either the irradiance or vector irradiance. The expression presented here holds for any number of polyhedral blockers and requires only a minor extension of standard polygon clipping to evaluate. To illustrate its use, three related applications are briefly described: direct computation of isolux contours, finding local irradiance extrema, and iso-meshing. Isolux contours are curves of constant irradiance acrossasurface that can be followed using a predictor-corrector method based on the irradiance Jacobian. Similarly, local extrema can be found using a descent method. Finally, iso-meshing is a new approach to surface mesh generation that incorporates families of isolux contours. © ACM 1994.

关键词： Mesh generation

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Utilizing the nurbs modeler Rhino® for economical and intuitive 3D product development

Utilizing the nurbs modeler Rhino&reg for economical and int...

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Proceedings: Electrical Insulation Conference and Electrical Manufacturing and Coil Winding Technology

作者： Acheson, Douglas C. Hardin, Jonathan D. Purdue Sch. of Eng. and Technology IUPUI Dept. of Comp. Graphics Technology IUPUI Computer Graphics Technology Program IUPUI

ISBN: (纸本)0941783235

Many manufacturing firms in today's economy are reluctant to engage their design personnel in costly, difficult to operate 3D CAD packages. While the attributes of designing in 3D are numerous and beneficial, committing to a high-end design software package often seems unjustifiable, especially when only a few new designs are required. An extremely attractive alternative to this dilemma is the integration of a powerful and innovative 3D modeling software called Rhinoceros®, or Rhino® for short. While costing substantially less than most 3D modeling programs, Rhino supplies an impressive array of advanced capabilities not found on many of the most powerful design software's on the market. Though not considered a parametric or feature-based modeler, Rhino often supplements these costly packages to accomplish complex surfacing challenges. This paper introduces this incredible program as it applies to the motor manufacturing industry and highlights the ease-of-use and incredible power of this modeling and presentation software. Additionally, an overview of different types of 3D modeling software is given in contextual reference to where this product may fit into a firm's design initiatives.

关键词： Product development

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A model of visual masking for computer graphics 97

A model of visual masking for computer graphics

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24th Annual Conference on computer graphics and Interactive Techniques, SIGGRAPH 1997

作者： Ferwerda, James A. Shirley, Peter Pattanaik, Sumanta N. Greenberg, Donald P. Program of Computer Graphics Cornell University 580 Rhodes Hall Ithaca United States University of Utah United States

ISBN: (纸本)0897918967

In this paper we develop a computational model of visual masking based on psychophysical data. The model predicts how the presence of one visual pattern aects the detectability of another. The model allows us to choose texture patterns for computer graphics images that hide the eects of faceting, banding, aliasing, noise and other visual artifacts produced by sources of error in graphics algorithms. We demonstrate the utility of the model by choosing a texture pattern to mask faceting artifacts caused by polygonal tesselation of a flat-shaded curved surface. The model predicts how changes in the contrast, spatial frequency, and orientation of the texture pattern, or changes in the tesselation of the surface will alter the masking eect. The model is general and has uses in geometric modeling, realistic image synthesis, scientic visualization, image compression, and image-based rendering. Copyright © 1997 by the Association for Computing Machinery, Inc.

关键词： Image compression

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A framework for the analysis of error In global illumination algorithms 94

A framework for the analysis of error In global illumination...

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21st Annual Conference on computer graphics and Interactive Techniques, SIGGRAPH 1994

作者： Arvo, James Torrance, Kenneth Smits, Brian Program of Computer Graphics Cornell University 580 Engineering and Theory Center Building IthacaNY14853 United States

ISBN: (纸本)0897916670

In this paper we identify sources of error in global illumination algorithms and derive bounds for each distinct category. Errors arise from three sources: inaccuracies in the boundary data, discretization, and computation. Boundary data consist of surface geometry, reflectance functions, and emission functions, all of which may be perturbed by errors in measurement or simulation, or by simplifications made for computational efficiency. Discretization error is introduced by replacing the continuous radiative transfer equation with a finite-dimensional linear system, usually by means of boundary elements and a corresponding projection method. Finally, computational errors perturb the finite-dimensional linear system through imprecise form factors, inner products, visibility, etc., as well as by halting iterative solvers after a finite number of steps. Using the error taxonomy introduced in the paper we examine existing global illumination algorithms and suggest new avenues of research. © ACM 1994.

关键词： Linear systems

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An interactive computer graphics approach to surface representation

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Communications of the ACM 1977年第10期20卷 703-712页

作者： Wu, Sheng-Chuan Abel, John F. Greenberg, Donald P. Department of Structural Engineering Cornell University Ithaca NY 14853 United States Program of Computer Graphics Cornell University Ithaca NY 14853 United States

An interactive computer graphics method has been developed for the rapid generation of arbitrary shaped three-dimensional surfaces. The method is a synthesis of spline theory and algorithms, an interactive means for man-machine communication, and software for static or dynamic graphics display. The basic technique employed is a modified lofting method in which sectional curves are represented by uniform B-splines and the surface is interpolated between sections by Cardinal splines. Among the features of this method are algorithm, which enable interactive modification of the B-spline representation of the sectional curves. At all stages of the process, the spatial information is graphically displayed to the user. Complex surfaces can be created by the combination of a number of shapes that have been separately generated and automatically joined. The system has been successfully interfaced to a variety of analytical routines for structural, medical and graphical applications. © 1977, ACM. All rights reserved.

关键词： computer graphics finite element input methods lofting splines three-dimensional surface representation

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Feature-Based Textures

Feature-Based Textures

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15th Eurographics Workshop on Rendering Techniques, EGSR 2004

作者： Ramanarayanan, G. Bala, K. Walter, B. Department of Computer Science Cornell University IthacaNY United States Program of Computer Graphics Cornell University IthacaNY United States

ISBN: (纸本)3905673126

This paper introduces feature-based textures, a new image representation that combines features and samples for high-quality texture mapping. Features identify boundaries within an image where samples change discontinuously. They can be extracted from vector graphics representations, or explicitly added to raster images to improve sharpness. Texture lookups are then interpolated from samples while respecting these boundaries. We present results from a software implementation of this technique demonstrating quality, efficiency and low memory overhead. © The Eurographics Association 2004.

关键词： Image enhancement

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3D scattered data approximation with adaptive compactly supported radial basis functions

3D scattered data approximation with adaptive compactly supp...

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6th International Conference on Shape Modeling and Applications

作者： Ohtake, Y Belyaev, A Seidel, HP Computer Graphics Group Max-Planck-Inst. für Informatik Germany Intgd. V-CAD System Research Program RIKEN Japan

ISBN: (纸本)0769520758

In this paper we develop an adaptive RBF fitting procedure for a high quality approximation of a set of points scattered over a piecewise smooth surface. We use compactly supported RBFs whose centers are randomly chosen from the points. The randomness is controlled by the point density and surface geometry. For each RBF its support size is chosen adaptively according to surface geometry at a vicinity of the RBF center All these lead to a noise-robust high quality approximation of the set. We also adapt our basic technique for shape reconstruction from registered range scans by taking into account measurement confidences. Finally, an interesting link between our RBF fitting procedure and partition of unity approximations is established and discussed.

关键词： adaptive RBF surface reconstruction from scattered data

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