Free Surface Of Reverse Engineering

Reverse engineering is a rapidly developing discipline, which integrates the developing technologies such as measurement technology, computer geometry a nd graphics processing. While conventional engineering transforms design cone epts and CAD models into real parts, in reverse engineering real parts are tra nsformed into design concepts and CAD models. Reverse engineering not only provides a new methods for product design, but also greatly shortens the desi gn cycle. In industrial areas such as automobiles, domestic electronics and so on, reverse engineering begins to play an important role. The parts reverseeng ineering deals with mostly have freeform surfaces.The regeneration of the free form surfaces is the main task of reverse engineering. In this paper some key techniques for NURBS surface reconstruction in reverse engineering such as B -spline curve fitting , B-spline surface fitting to scattered data ,B-spline surfa ce fitting to contour data and B-spline curve fairing are studied.The dissertation is summarized as follows:1) B-spline curve fitting is studied. Several curve fitting methods are disc ussed, and a method for B-spline curve fitting in the specified tolerance is pr esented.2) B-spline surface fitting is studied. Several surface fitting methods are d iscussed. the parametrization of scattered data ,the selection of knot vector, th e control of precision and the stability of the methods are analyzed, and the algorithm for B-spline surface fitting to scattered data in specified tolerance i s given. Especially, in order to assure the smooth connection between the adj acent surfaces, the surface fitting algorithm of interpolating four boundary cur ves and approximating inner scattered data is presented, the surface fitting al gorithm of interpolating four boundary curves and cross boundary derivative v ectors and approximating inner scattered data is also presented.3) B-spline surface fitting to contour data is studied. A fitting method of using uniform knot vector is given. Using this method, the resulted B-spline s urface not only satisfy the requirements of precision, but also possess fewer c ontrol vertices and good fairness, the computation speed is greatly improved t oo.4) B-spline curve fairing is studied. A fairing method based on energy me thod for cubic B-spline curves is presented.Since only local control vertices ar e modified, this method, compared with energy method, not only makes the c omputation faster, but also makes the changes in shape of curve less . Using this method ,we can obtain good B-spline curves.All the algorithms are verified.