Research On The Wavelet Analysis And Adaptive Mesh Fitting Of Reverse Engineering

Complex surface reconstruction in Reverse engineering (RE) is an important technology that can realize digital duplication of free-form surface parts and improvements, and it has a wide prospect. In general procedures of surface reconstruction, the measured point cloud is to pre-process, mesh, segment and then reconstruct surface that is segmented. In these ways, the process is proceeded slowly and cost-time, also can not promise the precision. Then direct surface reconstruction is arised, and it can realize the automation easily, also can pass the complex and un-controllable point segmentation process.Normally, non-contact measurement method is mostly used in data acquiring on surface. The laser we use that will make many randam noise data in the point cloud that is affect the quality of the reconstruct surface. For those randam noise data points are at high frequency, it arises that wavelet analysis theory can be applied in noise reduction, that can prove the quality of the surface reconstruction.In the paper, the theories, methods and characteristic of exiting measurement machine is studied. In the meanwhile, every method of free-form surface measurement is also comparied by a lot of parts'measurement. Based on the point cloud which is acquired by TDV800 laser scanner, pre-processing which includes data merge, filtering, noise reduction and coordinate transformation were observed, mostly in applying wavelet technology in denosing cloudy data. Denoising cloudy data based wavelet is the process of decomposing signal with wavelet, aquiring approximate coefficients and detail coefficient, acting detailed coefficient with threshold to suppress noises, then reconstruting signal to get the goal of denoising. After decomposing signal of wavelet, threshold value can be chosen in different level to suppress noises, that means the method is flexible. Most important is that the cloudy data can be judged whether it is a noise point data or not, by some principle.Besides, in the process of topology reconstruction, the scattered point cloud was divided at equal intervals, then be meshed to finish the point cloud reconstruction. The mesh is saved in the software and can be exported, then the mesh is divided to quadrilateral patch. The boudary curve of quadrilateral patch and the normal line to boundary curve are fitted by parametric curve, and a parametric surface will be constructed by fitting the boundary curve, normal line and the points. After that, the error between parametric surface and the mesh point data will be caculated. If the error is larger than the setting value, the quadrilateral patch will be divided, then fitted until the error is not larger than the setting value.Focus on the research contents of this paper, visual software was designed by using VC++ programming and OpenGL graphics library and MATLAB. The operation of this software and the realize procedure of wavelet denoising and adaptive mesh fitting were demonstrated by point cloud samples of"leaf","vane"and"face".