Study On The Theory And Technology Of Quadric Surface Feature Extracting Based On Point Cloud

With regard to CAD modeling in reverse engineering (RE), some key techniques, including feature extraction from point cloud and parametric representation, are studied. For a new solution this thesis aims at the feature-based CAD modeling and especially focuses on the quadric surface extracting and optimizing with given constrains.The technique of segmenting and feature identifying is the bottle-neck problem of CAD modeling in RE. Feature extracting from point cloud directly and then CAD modeling with the feature parameters is a significant process, and it can improve the efficiency and precision. Some key problems in this process are researched.Generally the surface of objects such as mechanical parts is mainly composed of quadric surface, free-form surface and blending surface, which are defined as features in this paper. In relation to the feature extracting, the first step is to extract the "simple" surfaces such as planes, natural quadric surfaces (spheres, cylinders and cones) and tori. Planes considered as degenerated quadric surfaces, the quadric surface feature extracting should be more important in RE.In the process of feature extracting, segmenting and surface fitting are nearly simultaneous, however surface fitting is regarded more. In this thesis how to extract the quadric surface feature from point cloud is addressed. Some algorithms, including plane fitting, sphere fitting, cylinder fitting and cone fitting are discussed and programmed with linear or non-linear least squares method (LSM). As an alternative solution tool, based on LSM and region growing, some new techniques of quadric surface feature extracting are explored also. Finally some theories and methods on free-form surface and blending surface feature extracting are discussed.The CAD modeling in RE covers not only the geometric features but also the constraints. Local individual surface fitting is not adaptive to the theory of parametric design and feature design. A new mathematical model is brought into RE by joining the feature extracting and constraints optimizing together, which seeks a global solution but not a single surface fitting. It makes the reverse design meet the user's purpose better.All the research work mentioned above is derived from practical background of reverse engineering CAD modeling and it owns strong applied value. In practical application, the methods presented in this thesis are proved to be successful, robust and satisfying.