LCD Mura缺陷的B样条曲面拟合背景抑制

针对机器视觉检测TFT-LCD Mura缺陷时存在的图像整体亮度不均匀、背景复杂等影响检测准确性的问题,提出一种基于B样条曲面拟合的背景抑制方法。在最小二乘法准则的约束下,采用双三次B样条曲面拟合算法拟合出背景,并添加光顺项调整拟合精度,用原始图像减去拟合背景,从而消除亮度不均匀背景对缺陷分割造成的影响。为提高算法速度,对原始图像进行分块拟合,并将双三次B样条函数分解为一元函数求解,减小了计算量,同时避免了对原函数求解时容易出现的病态解问题。实验结果表明,该算法准确、高效。     

用Loop细分曲面拟合点云数据的方法

将输入的点云数据进行三角剖分形成三角网格,按参考文献[1]建立求解插值细分曲面控制顶点的线性方程组.将所建立的线性方程组进行变换,使方程组的系数矩阵对称.证明了该系数矩阵正定,给出了矩阵特征值的上下界估计.将三角网格顶点作为迭代的初始控制点,提出了求解插值细分曲面控制顶点的两种迭代算法以及两个相应的盈亏修正公式.实例表明,两种迭代算法收敛速度快,拟合精度高.     

基于细分模式与能量优化的曲面混合方法

论述了用Catmull-Clark细分曲面及能量优化法对多张三次B样条曲面进行混合的方法。首先引入一种边界拓扑修改的细分规则，可生成逐段光滑的细分曲面，在此基础上构造多张三次B样条曲面的混合曲面，采用能量优化方法求解控制顶点。与现有方法相比，构造的混合曲面形状易于控制，能满足复杂的边界要求，且整个混合曲面除了在有限奇异点处为C^1连续外均达到C^2连续。     

一种可调的Catmull-Clark细分曲面

通过在曲面细分过程中引入一个参数t(0≤t≤1)，使得Catmull-Clark细分曲面可调，得出一种新的算法。这种算法简单直观，通过调节参数t值，可以得到一族细分曲面。该族细分曲面不但保留了许多Catmull—Clark细分曲面的特性，而又可以方便地解决在工程中经常遇到的调整曲面位置和形状的问题。同时，还可以将这种细分算法作为Catmull-Clark细分的前置处理方法。文中详细讨论了这一算法，并给出了验证实例。     

Butterfly细分曲面的快速求值

从分析Butterfly细分曲面的局部参数化出发,通过参数二进制分解生成数列以及构造细分格式的局部加细矩阵,并利用对应矩阵序列乘积与矩阵特征分解计算出控制点权值,从而解决TButterfly细分曲面插值问题.算法独立于网格存储的数据结构,避免了求邻接关系等费时的操作,并且容易推广到其他三角网格插值细分格式的曲面求值中.     

基于散乱数据的B样条曲面重构与优化

利用B样条曲面表示初始逼近曲面，利用三次B样条曲线优化曲面，实现了散乱数据的曲面重构，算例表明，算法简单易行，逼近效果良好。     

NURBS 曲面G1/G2光滑拼接方法

非均匀有理B样条(NURBS)因其优越的性能而在几何造型中校广泛应用。单片NURBS曲面具有较好的参数与几何连续的，性质，而在实际造型系统中，经常需要将不同的曲面片加以拼合。笔者利用G连续的充分条件及B样条基函数的导数，性质，构造了具有q阶公共边界的NURBS曲面之间实现G1(切平面连续)与G2(高斯曲率连续)光滑拼接的实用算法。即根据一个已知的NURBS曲面片，通过调整边界附近的部分控制点及权因子，以达到光滑拼接的目的。     

基于Catmull-Clark细分规则的双参数细分曲面

通过在曲面细分过程中引入两个参数,给出一种新的细分曲面构造的算法,使得所得的细分曲面可调.通过调节一个参数值,可以得到一族细分曲面.另一个参数是细分过程的改变参数,改变它的初值,也可得细分结果.最后给出了曲面设计的实例,表明这种算法简单、有效.     

一类C2连续可调控的交错B样条曲面

提出一类C^2连续可调控的带参数ε的交错B样条曲面的生成方法,这种曲面具有普通3次B样条曲面的主要性质,在控制点固定时,改变参数ε的值能调控曲面的位置,当ε→0时曲面整体地逼近于控制多面体网。     

基于C-B样条的三角形和四边形曲面生成

文章给出了基于C-B样条的由网格数据产生三角形和四边形曲面片的方法,C-B样条是由基底函数{sin t,cos t,t,1}导出的一种新型样条曲线,它可以克服现在正在使用的B样条和有理B样条为了满足数据网格的拓扑结构而增加多余的控制点,求导求积分复杂繁琐,阶数过高,从而讨论其连续拼接时增加了困难等缺点,如何将它推广成曲面就成为一个重要问题。作者利用边-顶点方法构造插值算子,再将这些算子进行凸性组合,将C-B样条曲线推广成三角形曲面片和四边形曲面片,它可以用于CAD的逆向工程中散乱数据的曲面重构。     

基于插值与逼近的复杂曲面拟合

工程图纸和实物模型提供的曲面原始数据通常具有分布不均匀的特点，如果直接使用四边域或三边域曲面进行拟合，曲面的光顺性将无法保证。针对这种情况，笔者利用插值与逼近相结合的曲面拟合思路，构造了由初始曲面拟合、曲面逼近、及曲面细化等3个步骤组成的曲面造型方法。实践表明，这种方法能较好地解决原始数据点分布不均匀的曲面造型问题。     

Subdivision surface-based finish machining

Subdivision surfaces combine smooth spline surfaces and polygonal meshes together, therefore, a smooth design model and discrete machining models may be unified and subdivision surfaces may be used as a common representation for geometric design and machining. Motivated by the idea, this paper presents the study of finish machining of objects represented by subdivision surfaces with emphasis on geometric error control involved in tool-path generation. First, given a design model, chordal error is controlled during finishing model building. A chordal error-driven adaptive subdivision method is used to build finishing models with less data. Second, a surface decomposition machining strategy is used to control the cusp height error. A simple iso-slope curve tracing and surface decomposition algorithm is presented to partition the model into flat and steep regions. Contour-map tool-paths are generated in the steep regions while iso-planar tool-paths are generated in the flat regions. The gouge problem is easily handled through two-dimensional (2D) tool-path correction algorithms. The implementation results demonstrate that subdivision is capable of serving as a unified representation for both geometric modelling and machining.     

基于细分网格的多分辨率几何数据压缩方法研究

提出了一种基于细分网格的多分辨率几何数据压缩算法 ,该算法是一种利用正则曲面法线向量特性及细分曲面的细分连通性的有损压缩方法 ,因此可以获得很高的压缩比     

Reconstruction of Two-Dimensional Randomly Rough Surfaces Based on Bidirectional Reflectance Distribution Function

This article presents an inverse method for reconstructing two-dimensional randomly rough surfaces based on the available (experimental or given) data of the bidirectional reflectance distribution function (BRDF). The Maxwell’s equations of electromagnetic waves are applied to describe the light scattering process of rough surfaces by accounting for the near-field effect. Such a forward problem is numerically solved with the finite-difference time-domain algorithm. The inverse scattering problem of reconstructing the surface profile is handled by means of an optimization technique—the particle swarm optimizer algorithm. As an example, reconstruction of a Gaussian rough surface is conducted based on the experimental data of BRDFs. The retrieved results of the surface profile are compared with those measured by atomic force microscopy from the samples, which shows that the reconstruction algorithm can provide the credible prediction of surface profiles. The reconstruction approach studied in this study can make reliable predictions of the actual or required surface profiles.     

Subdivision shells with exact boundary control and non‐manifold geometry

We introduce several new extensions to subdivision shells that provide an improved level of shape control over shell boundaries and facilitate the analysis of shells with non‐smooth and non‐manifold joints. To this end, extended subdivision schemes are used that enable to relax the continuity of the limit surface along prescribed crease edges and to create surfaces with prescribed limit positions and normals. Furthermore, shells with boundaries in the form of conic sections, such as circles or parabolas, are represented with rational subdivision schemes, which are defined in analogy to rational b‐splines. In terms of implementation, the difference between the introduced and conventional subdivision schemes is restricted to the use of modified subdivision stencils close to the mentioned geometric features. Hence, the resulting subdivision surface is in most parts of the domain identical to standard smooth subdivision surfaces. The particular subdivision scheme used in this paper constitutes an improved version of the original Loop's scheme and is as such based on triangular meshes. As in the original subdivision shells, surfaces created with the modified scheme are used for interpolating the reference and deformed shell configurations. At the integration points, the subdivision surface is evaluated using a newly developed discrete parameterization approach. In the resulting finite elements, the only degrees of freedom are the mid‐surface displacements of the nodes and additional Lagrange parameters for enforcing normal constraints. The versatility of the newly developed elements is demonstrated with a number of geometrically nonlinear shell examples. Copyright © 2011 John Wiley & Sons, Ltd.     

动态隐式曲面高质量三角化

提出了一种新的动态隐式曲面的快速、高质量绘制方法。该方法首先用粒子分裂和漂移实现隐式曲面均匀采样,然后用滚球法(BPA)法对均匀采样点进行快速三角化,最后用细分法对重建网格进行细分,从而得到高质量的隐式曲面多边形化模型。对于动态变化的隐式曲面,该方法充分利用变化前后的连贯性,实现动态隐式曲面的快速绘制。     

A new machine strategy for sculptured surfaces using offset surface

A new CNC tool path planning method is developed for accurate and efficient finishing cutting of sculptured surfaces. The proposed method generates CNC tool paths based on an offset surface of an object instead of the actual surface. The new algorithm consists of two main computational techniques: offset surface generation technique and offset CNC tool path planning technique. In offset surface generation, approximate parametric offset surfaces are generated accurately from an original parametric surface by employing bi-cubic surface patch, surface conversion, and surface subdivision algorithms. In offset CNC tool path planning, the precise geometric models of chordal deviation and cusp height on an offset surface are established. The effectiveness of this proposed CNC tool path planning method is verified by geometric simulation and verification which detect and identify errors in CNC tool paths.     

Automatic metric 3D surface mesh generation using subdivision surface geometrical model. Part 2: Mesh generation algorithm and examples

In this paper, a new metric advancing front surface mesh generation scheme is suggested. This new surface mesh generator is based on a new geometrical model employing the interpolating subdivision surface concept. The target surfaces to be meshed are represented implicitly by interpolating subdivision surfaces which allow the presence of various sharp and discontinuous features in the underlying geometrical model. While the main generation steps of the new generator are based on a robust metric surface triangulation kernel developed previously, a number of specially designed algorithms are developed in order to combine the existing metric advancing front algorithm with the new geometrical model. As a result, the application areas of the new mesh generator are largely extended and can be used to handle problems involving extensive changes in domain geometry. Numerical experience indicates that, by using the proposed mesh generation scheme, high quality surface meshes with rapid varying element size and anisotropic characteristics can be generated in a short time by using a low‐end PC. Finally, by using the pseudo‐curvature element‐size controlling metric to impose the curvature element‐size requirement in an implicit manner, the new mesh generation procedure can also generate finite element meshes with high fidelity to approximate the target surfaces accurately. Copyright © 2003 John Wiley & Sons, Ltd.