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New algorithms for evaluating parametric surface

Progress in Natural Science:Materials International 2001年第2期 64-70页

作者：王国瑾成敏 China Hangzhou 310027 Institute of Computer Images and Graphics State Key Laboratory of CAD&CG Zhejiang University

Through generalization of mathematical model of surface lofting program in the CONSURF system, the definitions for two generalized Ball surfaces and their recursive algorithms are given. Furthermore, the conversion algorithms from Bezier surface to these two generalized Ball surfaces are presented. On the basis of these algorithms, two more efficient algorithms for evaluating parametric surfaces are also derived. One uses generalized Ball forms directly for evaluating surface, and the other converts the given Bezier surface to a generalized Ball surface firstly, and then evaluates the surface. Both theoretical analysis and example computations show that the two new algorithms are more efficient than the de Casteljau algorithm. Especially when Wang-Ball surface is used, the time complexity is reduced from cubic to quadratic of the degree of the surface. If these algorithms are applied to displaying, interactive rendering, designing, intersection-finding, offsetting and approximating for surfaces, conside

关键词： Bezier surface generalized Ball surface evaluating algorithm time complexity.

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Topology recognition of 3D closed freeform objects based on topological graphs

Topology recognition of 3D closed freeform objects based on ...

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Pacific Conference on computer graphics and Applications

作者： D. Steiner A. Fischer CMSR Laboratory for Computer Graphics and CAD Department of Mechanical Engineering Technion-Israel Institute of Technology Haifa Israel

ISBN: (纸本)0769512275

Reverse engineering (RE) deals with an enormous number of irregular and scattered digitized points that require intensive processing in order to reconstruct the surfaces of an object. Surface reconstruction of freeform objects is based on geometrical and topological criteria. Current fitting methods reconstruct an object using a bottom-up approach, from points to a dense mesh, and finally into smoothed connected freeform sub-surfaces. This type of reconstruction, however, can cause topological problems that lead to undesired surface fitting results. Such problems are particularly common with concave shapes. To avoid problems of this type, the paper proposes a new method that automatically detects the topological structure of an object as a base for surface fitting. The topological reconstruction method described in the paper is based on two stages: (1) creating 3D non-self-intersecting iso-curves from a 3D triangular mesh and (2) extracting a topological graph. The feasibility of the proposed topological reconstruction method is demonstrated on several examples using freeform objects with complex topologies.

关键词： Topology Surface fitting Surface reconstruction Shape Reconstruction algorithms Reverse engineering Laboratories computer graphics Mechanical engineering Scattering

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Adaptive reconstruction of freeform objects with 3D SOM neural network grids

Adaptive reconstruction of freeform objects with 3D SOM neur...

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Pacific Conference on computer graphics and Applications

作者： J. Barhak A. Fischer CMSR Laboratory for Computer Graphics and CAD Department of Mechanical Engineering Technion-Israel Institute of Technology Haifa Israel

Reverse engineering is an important process in cad systems today. Yet several open problems lead to a bottleneck in the reverse engineering process. First, because the topology of the object to be reconstructed is unknown, point connectivity relations are undefined. Second, the fitted surface must satisfy global and local shape preservation criteria that are undefined explicitly. In reverse engineering, object reconstruction is based both on parameterization and on fitting. Nevertheless, the above problems are influenced mainly by parameterization. In order to overcome the above problems, the paper proposes a neural network, Self Organizing Map (SOM) method, for creating a 3D parametric grid. The main advantage of the proposed SOM method is that it detects both the orientation of the grid and the position of the sub-boundaries. The neural network grid converges to the sampled shape through an adaptive learning process. The SOM method is applied directly on 3D sampled data and avoids the projection anomalies common to other methods. The paper also presents boundary correction and growing grid extensions to the SOM method. In the surface fitting stage, an RSEC (Random Surface Error Correction) fitting method based on the SOM method was developed and implemented.

关键词： Neural networks Surface fitting Reverse engineering Surface reconstruction Shape Spline Laser modes Data mining Jacobian matrices Laboratories

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Mechanically based design: adaptive refinement for B-spline finite element

Mechanically based design: adaptive refinement for B-spline ...

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International Conference on Shape Modeling and Applications

作者： P. Kagan A. Fischer P. Bar-Yoseph Laboratory for Computer Graphics and CAD Mechanical Engineering Department Technion-Israel Institute of Technology Haifa Israel Computational Mechanics Laboratory Mechanical Engineering Department Technion-Israel Institute of Technology Haifa Israel

ISBN: (纸本)0769508537

This paper presents a method for adaptive refinement within an integrated mechanically based CAE system. The system uses a mechanical B-spline finite element model for both geometric design and mechanical analysis. A technique for locally refining a solution by B-spline finite elements is presented. The key component in the proposed method is the linear coordinate transformation introduced into the refined element. The transformation is constructed in such a way that the transformed nodal configuration of the refined element is identical to the nodal configuration of the neighbor elements. Therefore, the assembly proceeds in the regular fashion, while the C/sup 0/ continuity is forced along the inter-element boundary exactly. The proposed adaptive refinement method has been implemented both for surface and solid design without substantial differences in technical complexity. Its feasibility as applied to sculptured surface and solid objects is demonstrated by several examples.

关键词： Spline Finite element methods computer aided engineering Shape Laboratories Solid modeling Algorithm design and analysis computer graphics Design automation Mechanical engineering

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A graphic view of linear algebra

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computer-Aided Design 2000年第4期32卷 295-295页

作者： A Fischer Technion—Israel Institute of Technology Faculty of Mechanical Engineering CMSR Laboratory for Computer Graphics and CAD Haifa Israel

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Adaptive parameterization for reconstruction of 3D freeform objects from laser-scanned data 7

Adaptive parameterization for reconstruction of 3D freeform ...

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7th Pacific Conference on computer graphics and Applications, Pacific graphics 1999

作者： Fischer, A. Manor, A. Barhak, Y. CMSR Laboratory for Computer Graphics and CAD Department of Mechanical Engineering Technion - Israel Institute of Technology Haifa32000 Israel

ISBN: (纸本)0769502938

This paper proposes a new adaptive parametrization method to overcome the problems of using laser scanners in Reverse Engineering. The method is based on the following stages: (a) Detecting a 3D boundary of the parametric base surface by matching an intensity image from a CCD camera with the scanned data. (b) Adaptively reconstructing a parametric base surface with a non-self intersecting grid, based on a PDE method (c) Calculating the parametrization of the 3D sampled points. (d) Fitting the surface by applying a least square (LSQ) approximation method with boundary constraints. The feasibility of the parametrization algorithm is demonstrated on several examples using sculptured free objects. © 1999 IEEE.

关键词： Reverse engineering

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Virtual 3D sculpturing with a parametric hand surface 98

Virtual 3D sculpturing with a parametric hand surface

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computer graphics International

作者： J.P.Y. Wong R.W.H. Lau Lizhuang Ma Computer Graphics and Media Laboratory Department of Computing Hong Kong Polytechnic University Hong Kong China Department of Computer Science City University of Hong Kong Hong Kong China State Key Laboratory of CAD&&G University of Zhejiang Hangzhou China

ISBN: (纸本)9780818684456

Many techniques have been developed for 3D object deformation. These techniques have been widely used in most cad/CAM systems. Intuitive while efficient methods for interactive 3D object deformation in a VR environment, however, are rare. One of our current research projects is to develop such a technique based on the use of a sensor glove. The idea is to create a hand surface interpolating through all the data points of the sensor glove. Through mapping the vertices of an object model to the hand surface, the object model may be deformed simply by changing the hand gesture. An initial method for implementing this idea was presented in our recent paper. In this paper, we discuss some of the limitations of the earlier method and present a refined method that overcomes most of the limitations. The resulting method is both efficient and intuitive as demonstrated by the results of our experiments.

关键词： Deformable models Lattices Layout Laboratories Virtual reality computer graphics computer science computer aided manufacturing cadCAM Tensile stress

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Two-stage algorithm for determination of the bending sequence in sheet metal products

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JOURNAL OF MECHANICAL DESIGN 1997年第2期119卷 259-266页

作者： Radin, B Shpitalni, M Hartman, I Laboratory for Computer Graphics and CAD Technion-Israel Institute of Technology Haifa Israel 32000

This paper presents an algorithm for solving the complex and critical problem of bending sequence in sheet metal manufacturing. Finding the bending sequence and required tool assignment presents a large combinatorial problem which is impossible to solve optimally for practical applications within a reasonable period of time. The paper presents a two-stage algorithm. The first stage finds a feasible solution based upon collision avoidance heuristics. The second stage rapidly seeks an alternative feasible sequence with a lower cost without exceeding time limitations. The algorithm is very practical because it reaches a low-cost solution quickly within computer memory limitations. In this paper, the problem is defined, the approach is presented formally, and finally, the power of the algorithm is demonstrated by solving bending sequences for real products.

关键词： algorithms Metal products Feasible Solution time periods Sheet metal Bending double-stage

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Optimization-based reconstruction of a 3D object from a single freehand line drawing

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computer-AIDED DESIGN 1996年第8期28卷 651-663页

作者： Lipson, H Shpitalni, M Laboratory for Computer Graphics and CAD Faculty of Mechanical Engineering Technion Haifa 32000 Israel

This paper describes an optimization-based algorithm for reconstructing a 3D model from a single, inaccurate, 2D edge-vertex graph. The graph, which serves as input for the reconstruction process, is obtained from an inaccurate freehand sketch of a 3D wireframe object. Compared with traditional reconstruction methods based on line labelling, the proposed approach is more tolerant of faults in handling both inaccurate vertex positioning and sketches with missing entities. Furthermore, the proposed reconstruction method supports a wide scope of general (manifold and non-manifold) objects containing flat and cylindrical faces. Sketches of wireframe models usually include enough information to reconstruct the complete body. The optimization algorithm is discussed, and examples from a working implementation are given. Copyright (C) 1996 Elsevier Science Ltd.

关键词： drawing to model optimization robustness

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Two-stage algorithm for rapid determination of the bending sequence in sheet metal products

Two-stage algorithm for rapid determination of the bending s...

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ASME 1996 Design Engineering Technical Conferences and computers in Engineering Conference, DETC-CIE 1996

作者： Radin, B. Shpitalni, M. Hartman, I. Laboratory for Computer Graphics and Cad Faculty of Mechanical Engineering Technion - Israel Institute of Technology Haifa32000 Israel

ISBN: (纸本)9780791897591

关键词： Sheet metal

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