Rearch On The Modeling Technology Of The Freeform Surface Base On The Point Clould

The freeform surface modeling is an important researching content in reverse engineering. The precision and quality of the modeling play a significant guarantee in manufacturing high quality parts quickly. So it has important theoretical significance and utility value to study freeform surface modeling technique based on scanning point cloud.Scanning point cloud is the foundation of freeform surface modeling. It obtains three dimensions data information of sample's surface outline though three-dimension laser scanning system. This paper aims at analyzing and processing scanning point cloud, setting up mathematical model of curve and surface, reversing CAD model of sample.In this paper, the methods of data unify, noise-removal process, data compression technique, technology of mending and dividing are researched. Thereinto, the data is unified the same reference frame by the method of the coordinate transform. based on visual examination, curve examination and the dispatch of the chords, a method on the base of adjacent field to realize noise-removal process is put forward. data compression technique is done based on curvature variation. The practice proves that this method has the advantages of good effect on noise-removal process, high efficiency of data compression, and greatly improved of uniformity coefficient. During the reconstruction procedure of curve and surface, based on the theories of least squares fitting, chebyshev curve fitting and NURBS curve and surface fitting, the method and process of inverse computation of reference point by model value point, and the method of curve surface fitting of four sides region gridding and triangle gridding are researched. Besides, theoretical analysis, algorithm design and program composition are completed. The result of the simulation test indicates that fitting precision is not proportional to fitting rank. When the rank achieves definite value, the precision shows stabilization, which offer gist for choosing method of fitting.Based on the discussing of curve and surface fitting, this paper research on the methods of geometric continuity of curve and surface joint and curve surface smoothing, and then present the method of combine surface joint and smoothing and the criterion of the qulity of the fitting surface.A new software"MySFD"are developed, which based on freeform surface modeling of scanning point cloud, Visual C++ and OpenGL. The software has the basic function of curve and surface modeling from thepoint cloud. Besides, it can observe and dispose all the process of freeform surface modeling visually, and obtain the feedback result of calculation and analysis at any moment.