Research And Application Of Wavelet Technology Based On Reverse Engineering

Reverse Engineering(RE) is one important method to develop new product, which hasreceived more and more high attention both from industry and academia. Aiming at thecurrent questions in RE such as low automation and generality, lacking adaptivity, the newtime-frequency tool- wavelet technology is introduced。With a view to raise quality andefficiency, the key technologies including data treatments, data simplification, quasi-uniform B-spline curve fairness, NURBS surface reconstruction, wavelet decompositionand accuracy analysis of CAD model of reconstructed surface are researched anddiscussed.Coordinate transformation, coordinate fusion, delamination and ordering of cloudydata based on CMM are researched. According to the concentrating extent of coordinatevalue, fixed axis is identified automatically, so delaminating data is realized. On theprinciple of distance between data set, the method of judging beginning and end is adoptedto order, and so topology information within same layer is established.The deleting method of abnormal noises is researched. Incorporating the, 3σlaw ofmathematical statistics, by means of calculating mean and standard error to determinatethreshold, the adaptive counting threshold method is put forward, which has welladaptivity.Denoising cloudy data based wavelet technology is researched. Using wavelet tech-nology to denoise is the process of decomposing signal with wavelet, acquiring approxi-mate coefficients and detail coefficients, acting detailed coefficients with soft threshold tosuppress noises, then reconstructing signal to get the goal of denoising.The key of simplifying data technique is retaining original features of cloudy datautmost. On the basis of researching current simplification technique, new method usingsecond generation wavelet based on lifting to simplification data is proposed.Quasi-uniform B-spline curve fairness technique is studied and new method of curvefairness with second generation wavelet based on lifting is presented. From the conceptionof MRA, wavelet representation of B-spline curve is reasoned in detail, semi-orthogonalB-spline wavelet is introduced and B-spline wavelet fast algorithm of decomposing andreconstructing are given.Using the fundamental principle of second generation wavelet,after split, prediction and update, second generation wavelet representation of B-splinecurve is reasoned detailedly, and curve fairness based on second generation is realized. Fairness technique of B-spline curves with arbitrary control points based on wavelet isstudied. Refined curves meeting with the requirement of wavelet fairness are constructedby means of inserting knots to increase control points number.As reconstructing Non-Uniform Rational B-Spline (NURBS) surface, In order togenerate rectangle field grids, with non-uniform data points, a method of accumulatingchord length is presented to create non-uniform knots vector, Non-uniform B-Spline curveis constructed and interpolated on scanning line data points, then sampling it uniformly; Sothe accuracy of interpolated surface is guaranteed.The fast algorithms of quasi-uniform bi-cubic B-spline wavelet and decomposing dualcubic quasi-uniform B-spline surface are given. Re-sample point number which meets thecondition of wavelet decomposition is determined and seamless integration of surfacereconstruction and multi-rank decomposing it is realized.From the source of error, all sort of factors of influencing CAD model precision ofreconstructed surface are analyzed concretely. Evaluation methods of model precision areintroduced briefly and strategies dealing with error are proposed qualitatively. Thefeasibility and accuracy of algorithms of NURBS surface reconstruction anddecomposition with wavelet are verified through testing fairness and error.Adopting object-oriented programming technique, prototype system with wellapplication is tapped.