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

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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SEPARATION OF DISCONNECTED MACHINING REGIONS ON THE BASIS OF A CSG MODEL

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computer-AIDED DESIGN 1994年第1期26卷 46-58页

作者： SHPITALNI, M FISCHER, A [a]Laboratory for Computer Graphics CAD Faculty of Mechanical Engineering Technion-Israel Institute of Technology Haifa 32000 Israel

The process of converting a given design into the form of a rawstock minus a series of machining features is known as machining-features extraction. One step towards automatic machining-features extraction is the extraction of machining regions. The paper is concerned with the extraction of machining regions from the constructive-solid-geometry representation of a given object. The proposed method for the extraction of machining regions is based on manipulating the original CSG tree, representing the object, evaluating the various machining regions by using octrees, and pruning the CSG tree accordingly. If necessary, an additional stage of compacting follows. As a result, each machining region is represented by a compact CSG tree offering the following advantages. The CSG tree to be analysed is reduced in size, and thus the problem of machining-features extraction is simplified. The information is compact and concise. Moreover, no information is lost (CSG representation is kept rather than boundary representation), and the designer's intensions are conveyed to the process planner more clearly. In the special case in which the machining regions are identical to machining features, the method does offer the automatic extraction of machining features. In addition, the nesting level of the various machining regions is determined when needed.

关键词： FEATURE RECOGNITION CONSTRUCTIVE SOLID GEOMETRY CSG MODELS OCTREES CUTTER-PATH GENERATION

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DESIGN BY INTERPOLATION

DESIGN BY INTERPOLATION

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COMPEURO 93 : computerS IN DESIGN, MANUFACTURING AND PRODUCTION

作者： WEISS, M SHPITALNI, M Laboratory for Computer Graphics CAD Faculty of Mechanical Engineering Technion Haifa Israel

ISBN: (纸本)0818640308

The paper deals with design of shapes by interpolation, that is, cases where the desired shape is somehow "in between" two given shapes. The main issues involved in design by interpolation are: (a) capturing the "nature" (behavior) of the guiding shapes A and B;(b) attaining automatic correspondence between points (i.e., which point in shape A should be associated with which point in shape B);and (c) determining the interpolation method In the paper, new techniques for capturing the "nature" of shapes and for determining automatic correspondence of points are presented. Examples for interpolation of polygons, curves (Bezier and NURBS) and suvaces are included. The possibility of future design based upon extrapolation, rather than interpolation,is also discussed. © 1993 IEEE.

关键词： Bezier cad Interpolation NURBS Shape Design

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Verification of scanned engineering parts with cad models based on discrete curvature estimation

Verification of scanned engineering parts with CAD models ba...

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作者： Lipshitz, B. Fischer, A. Laboratory for Computer Graphics and CAD Department of Mechanical Engineering Technion-Israel Institute of Technology Haifa Israel

The manufacturing industry constantly needs to verify machined objects against their original cad models. Given a prototype design, an engineer should be able to determine whether the part was manufactured well;that is, whether it fits the cad model exactly. However, derivative computations are unstable for real data, and the estimated curvature is thus very sensitive to noise. Moreover, in many cases, spatial fitting of corresponding points is not sufficient. The current work utilizes the curvature properties to inspect manufactured parts that have been reconstructed from noisy and densely sampled data. Copyright © 2005 by ASME.

关键词： computer aided design

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Optimization-based reconstruction of a 3D object from a single freehand line drawing 07

Optimization-based reconstruction of a 3D object from a sing...

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ACM SIGGRAPH 2007 - International Conference on computer graphics and Interactive Techniques

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

ISBN: (纸本)9781450318235

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 free-hand 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 © 1996 Elsevier Science Ltd.

关键词： Three dimensional computer graphics

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

There are several open problems that are viewed as a bottleneck in the reverse engineering process: (1) The topology is unknown;therefore, point connectivity relations are undefined. (2) The fitted surface must satisfy global and local shape preservation criteria, which are undefined explicitly. The reconstruction is based on parameterization and fitting stages. However, the above problems are influenced mainly by the parameterization. To overcome the above problems, the neural network self-organizing map (SOM) method is proposed for creating a 3D parametric grid. The main advantage of the SOM method is that it detects the orientation of the grid and the position of the sub-boundaries. Then through an adaptive process the neural network grid is converged to the sampled shape. The SOM method is applied directly on a 3D grid and avoids projection anomalies, which are common to other methods. For the surface fitting stage the random surface error correction fitting method, which is based on the SOM method, was developed and implemented. © 2002 Elsevier Science Ltd. All rights reserved.

关键词： Reverse engineering

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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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Adaptive tool path generation from measured data

Adaptive tool path generation from measured data

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作者： Yin, Z. Computer Graphics and CAD Laboratory School of Mechanical Engineering Shanghai Jiaotong University Shanghai 200030 China

Conventional algorithms for tool path generation from measured points did not use the region-by-region idea to generate adaptive tool paths since it is difficult to obtain geometric information of scattered points directly, which is necessary for adaptive tool path generation. This paper presents a new strategy for determining geometric information of physical parts measured and then three-axis numerically controlled (NC) adaptive (region-based) tool paths that overcome the inherent drawback (redundant tool paths) can be directly generated from measured points. A new algorithm for computing offsets of B-spline surfaces constructed using chosen point data as control points is also proposed in the paper.

关键词： Adaptive systems

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CNC interpolators: algorithms and analysis

CNC interpolators: algorithms and analysis

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Proceedings of the 1993 ASME Winter Annual Meeting

作者： Koren, Y. Lo, C.C. Shpitalni, M. Department of Mechanical Engineering University of Michigan Ann Arbor MI United States Laboratory for Computer Graphics and CAD Faculty of Mechanical Engineering Technion Haifa Israel

ISBN: (纸本)0791810291

cad systems today interpolate general curves by dividing each curve into many straight-line segments which are downloaded to the CNC. Determining the number of lines to be transferred from the cad to the CNC poses a conflict between the desired precision of the part and the feedrate fidelity. The current method results in severe variations in the feedrate, leading, in turn, to variations in the surface smoothness and a substantial increase in machining time. These problems are caused by the acceleration/deceleration at the ends of each segment. Moreover, the problems are inherent in the CNC interpolator, as is thoroughly discussed in this paper. These problems can be solved by the development of curve interpolation algorithms for CNC. In this paper, a real-time interpolation algorithm for curves presented in their parametric forms is proposed and compared with the existing cad interpolators. Analysis shows that with this new interpolator, a constant feed is maintained along the cut and the machining time is as expected. In addition, the amount of geometric information transferred from the cad system to the CNC is reduced by orders of magnitude. Moreover, the contour errors caused by the new interpolator are much smaller than those caused by conventional cad interpolators.

关键词： Numerical control systems

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Planar parameterization for closed 2-manifold genus-1 meshes

Planar parameterization for closed 2-manifold genus-1 meshes

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Ninth ACM Symposium on Solid Modeling and Applications, SM'04

作者： Steiner, D. Fischer, A. Laboratory for Computer Graphics and CAD Faculty of Mechanical Engineering Technion - Israel Institute of Technology Haifa 32000 Israel

Parameterization of 3D meshes is important for many graphics and cad applications, in particular for texture mapping, re-meshing and morphing. Current parameterization methods for closed manifold genus-n meshes usually involve cutting the mesh according to the object generators, fixing the resulting boundary and then applying the 2D position for each of the mesh vertices on a plane, such that the flattened triangles are not too distorted and do not overlap. Unfortunately, fixing the boundary distorts the resulting parameterization, especially near the boundary. A special case is that of closed manifold genus-1 meshes that have two generators. They can therefore be flattened naturally to a plane without the use of a fixed boundary while still maintaining the continuity of the parameterization. Therefore, in treating genus-1 objects, this attribute must be exploited. This paper introduces a generalized method for planar parameterization of closed manifold genus-1 meshes. As in any planar parameterization with a fixed boundary, weights are assigned over the mesh edges. The type of weights defined depends on the type of mesh characteristics to be preserved. The paper proves that the method satisfies the non-overlapping requirement for any type of positive barycentric weights, including nonsymmetrical weights. Moreover, convergence is guaranteed according to the Gauss-Seidel method. The proposed method is simple to implement, fast and robust. The feasibility of the method will be demonstrated on several complex objects.

关键词： computer aided design

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