【作者】 陈飞舟；

【导师】 叶修梓；

【作者基本信息】 浙江大学 ， 计算机应用技术， 2006， 硕士

【摘要】 作为产品设计制造的一种手段,20世纪90年代初,逆向工程技术开始引起各国工业界和学术界的高度重视。随着计算机技术及测量技术的发展,逆向工程已经成为新产品开发、消化以及吸收先进技术的重要途径。 曲面重构,是指从散乱数据点重构出物体的几何模型,并获得该几何模型的数学表达式,它是逆向工程研究中的关键内容。目前,大多数商品化CAD软件采用非均匀有理B样条(NURBS)作为自由曲面的表达形式。 本文在研究散乱点列曲面重构的基础上,针对三维网格模型的特殊性,提出了面向网格数据的曲面特征识别和构造算法。文章重点阐述了二次曲面、拉伸面、旋转面、以及一般自由曲面的构造方法。 二次曲面的应用非常广泛,目前,提取方法主要采取最小二乘法,由于求解的非线性(平面除外),导致算法效率低且准确性差。本文利用二次曲面的高斯图特性,识别曲面类型,并根据该类型对网格去噪,抽取符合该曲面特征的子网格,最后生成二次曲面。大量实验表明,此方法具有较好的稳定性、准确性,且算法效率较高。 拉伸面、旋转面在逆向工程中也占有一定的地位,算法的关键在于拉伸方向和旋转轴向的提取。对于拉伸面,本文在深入分析其高斯图特性的基础上,巧妙地提取了曲面的拉伸方向;而对于旋转曲面,本文引进了网格主方向的概念,并据此提取曲面轴向。 自由曲面的构造一直是逆向工程研究的热点。由于点列的散乱性质,导致一般的曲面拟合算法效率低,且边界不易控制。本文通过一定的方法,将散乱点列转化为有序点列,进而利用有序点列拟合的高效性,完成网格模型的曲面构造。此方法拟合精度高,对于多数的网格模型,均可以得到较好的结果。更多还原

【Abstract】 Reverse Engineering (RE), as a method of product designing and manufacturing, has been paid more and more attentions by the whole world during last 90’s.With the development of computer science and measure technique, it has already become as a key way of new product designing and advanced technique absorbing.Surface reconstruction, aiming to achieve the mathematical expression of geometric model for complex free-form surface from the scattered data, is a key technique of Reverse Engineering. Major commercial CAD software takes Non-Uniform Rational B-Spline (NURBS) as main expression presently.Through studying on the surface reconstruction upon randomly sampled points, improved surface fitting methods are put forward in this paper, aiming at triangle mesh. We explain the ways of surface reconstruction in details, including quadric surface, extruded surface, revolved surface and free-form surface.Least-square method is widely used to generate quadric surface at present, but the efficiency of it is low because of its non-collinear. With the help of Gaussian image, we propose a method here that denoise the mesh model first, then extract triangles which make up of the surface feature, finally we reconstruct the demanded surface. The exam results show that this approach is available and efficient.Extrude surface and revolved surface are also common in Reverse Engineering. The key of algorithm is to extract extruding direction or revolve axis direction. Based on deep analyzing on Gaussian image, we get the extruding direction magically. Also, we gain the revolve axis direction according to its primary directions.Free-form surface fitting is a hotspot in RE. The results of constructing surface directly upon randomly sampled points are always unacceptable. In this paper, we try to form ordered(m*n) points according to the mesh model, then we fit the given ordered points. Experiments show that the results are much better.更多还原