Research On Key Technology In Reconstruction Of Free-Form & Regular Surfaces In Reverse Engineering

In recent years, the arbitrary triangular mesh model acquisition from the existing physical object is more convenient with the development of coordinate measure system. So, the research of CAD model reconstruction from triangular mesh should be carried out urgently. A solution for reconstructing free-form & regular surfaces is deeply studied in this dissertation. The main research achievements are as following: (1) Algorithms of curvature estimation and triangular surface fairing are studied. A new algorithm is presented for fairing the triangular mesh by weighted average of the principle curvatures and principle directions. When fairing a specified local area, vertices are arranged on the closed loops beforehand so that the interior area can be well smoothed by setting smaller weights for inner loops. When comparing our new algorithm with the curvature-average fairing algorithm presented by Karbacher&H?usler, nearly the equivalent results are achieved when undergoing less iterates for a whole triangular mesh model. However, as iterates increasing, our new one has the advantage of less distortion and less volume variation and can produce better results. Otherwise, our new one also behaves better when fairing a local area. (2) Data segmentation, one of the most difficult technologies in reverse engineering, is studied. A feature-based data segmentation algorithm is developed through partition's border expanding based-on the character of triangular-mesh's data structure. Then the partitions can be optimized by several methods such as combining small partitions into adjacent one, decomposing cane partitions into neighbors and smoothing the borders. The final partitions coincide with the feature of objects. It is the foundation for later reconstruction of free-form & regular surfaces. (3) An approach of free-form surfaces reconstruction is studied and implemented. Firstly, a traced-projection algorithm, being efficient and meeting the requirements of interactive operation, is proposed for obtaining the path of two points on the triangular surfaces. Secondly, a feature-line optimization model, which can smoothly capture the object features, is established for producing better boundaries of quadrilateral domain. Latter, a uniformity resampling and force-balance-based uniformity refining procedure is proposed for reparametrization. Finally, better B-Spline surfaces are fitted because of the better quadrilateral domain and better reparametrization. The final result of our domain partition is pretty much the same thing that produced by Geomagic Studio, one of the famous software in reverse engineering. (4) An approach of regular surfaces reconstruction is studied. A projection-based moving least-squares method is studied and implemented for thinning the planar scatter points to a curve-like shape. Farther, the thin points can be approximated with B-Spline curve by ordering and parametering after reducing the number of points. The regular sweeping surfaces can be reconstructed after profile curves approximated by such B-Spline curves. Lots of experimental results demonstrate the algorithms proposed.