Study On Feature Technology In Reverse Engineering CAD Modeling

In this dissertation, the feature technology in reverse engineering is systematically studied. The key algorithms of the extraction and parametric representation of quadric surface and blend surface features are investigated and developed.Fundamental theories of feature in reverse engineering, such as feature definition, feature classification, feature representation and relationship between feature arid constraint, are introduced in chapter 2. A novel method of feature-based segmentation of point data is proposed. The feature points can be extracted from scan line data or point cloud by analyzing the curve and surface's curvature respectively.The well-known least squares method (LSM) is used to extract quadric surface feature. The linear and nonlinear LSM, such as method of normal equations (MNE), singular value decomposition (SVD) and eigenvector estimation (EVE), are discussed in chapter 3. New algorithms for fitting plane, sphere, cylinder and cone with linear and nonlinear LSM are discussed.A new method of extracting blend surface feature, including two steps: segmentation and recovery of parametric representation, is presented in chapter 4. The segmentation separates the points in the blend region from the rest of the point data with the processes of simplifying of point data, estimation of local curvature of surface and comparison of maximum curvature values. The recovery of parametric representation generates a set of profiles by marching throughout the blend region and fitting cylinders. The parameters of blend surface with constant radius or linear radius are analyzed and optimized with the theory of probability and statistics. Because of the existence of data points affected by noise, some causes to bring out extraction deviation are explored.With regard to the extraction of free-form surface feature, a practical method of re-parameterization of free-form surface is proposed with the combination of reverse engineering and conventional design methods. A slicing algorithm, used to get curves from point cloud, is presented in chapter 5. With the slicing and interaction analysis, the free-form surface features, including sweeping surface, rotational surface and skinning surface, can be cataloged.The technologies and key algorithms presented above are implemented in the reverse engineering CAD modeling software RE-SOFT. Two detailed examples are presented in chapter 6 to show the feasibility and application value of featuretechnique in reverse engineering CAD modeling.In the summary of this dissertation, a number of advanced topics for feature technique in reverse engineering are addressed for the future research.