Knot removal for parametric B-spline curves and surfaces

This paper is the third in a sequence of papers in which a knot removal strategy for splines, based on certain discrete norms, is developed. In the first paper, approximation methods defined as best approximations in these norms were discussed, while in the second paper a knot removal strategy for spline functions was developed. In this paper the knot removal strategy is extended to parametric spline curves and tensor product surfaces. The method has been implemented and thoroughly tested on a computer. We illustrate with several examples and applications.     

网格图形编辑的样条方法

提出基于样条的网格图形编辑方法,首先在网格表面附近构建近似的样条曲面,同时预计算网格顶点在样条上的对应点处局部标架下的坐标表示,并作为不变量在变形中进行保持;然后编辑样条的位置和形状,利用局部标架和细节坐标重建变形后的网格,同时进行网格光滑和网格细分,改善变形效果,以实现复杂模型简单快捷的编辑/变形.方法在保细节的同时允许对网格在多个尺度下编辑.实验结果表明,融合了样条的三角网格方法较传统的样条编辑方法可避免产生过多的控制点,大大地简化了操作.     

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。     

Local shape control of the rational interpolation curves with quadratic denominator

A rational cubic interpolating spline with quadratic denominator was constructed by Gregory and co-workers. This paper deals with the properties of the interpolation and local shape control of the interpolant curves. The methods of value control, convex control and inflection-point control of the interpolation at a point are developed. Some numerical examples are provided to illustrate these methods.     

Non-polynomial spline for solution of boundary-value problems in plate deflection theory

In this paper a non-polynomial quintic spline function is applied to the numerical solution of a certain fourth-order, two-point boundary-value problem occurring in plate deflection theory. Direct methods of orders two, four, and six have been obtained which lead to five-diagonal linear systems. Boundary formulae of various orders have been developed to retain the bandwidth of the coefficient matrix as five. Convergence analysis of the sixth-order method is given. Numerical results are provided to demonstrate the superiority of our methods.     

基于三坐标测量机的曲面测量规划方法

在三坐标测量中,测量路径的优化是实现曲面自动测量的基础。分析综述了常用的几种测量路径优化方法后,本文提出一种基于多项式法的三次样条插值法。通过实例的测量验证,并与多项式法进行比较,证实三次样条插值法可大大提高三坐标测量机的测量精度和效率。     

多重样条小波与微分方程自适应正交配置算法

０．引 言 由于小波的分层性,时－频空间的局部性,能量正交性等,使得它在构造微分方程自适应快速求解算法方面具有独特的应用价值．最近蔡伟等［８］通过构造一类能量内积意义下的紧支集半正交三次单重样条小波,得到了求解微分方程初边值问题的自适应样条小波结点配置算法．然而,三次样条结点配置解一般只能达到Ｏ（ｈ２）的逼近阶,而利用多重样条（如Ｈｅｒｍｉｔｅ样条）建立的正交配置格式却可以达到更高逼近阶．因此,构造能量内积意义下的紧支集半正交多重样条小波基,并建立相应的微分方程自适应小波快速正交配置算法是一项有意…     

Local control of interpolating rational cubic spline curves

A rational spline based on function values only was constructed in the authors’ earlier works. This paper deals with the properties of the interpolation and the local control of the interpolant curves. The methods of value control, convex control and inflection-point control of the interpolation at a point are developed. Some numerical examples are given to illustrate these methods.     

基于曲线和曲面控制的多边形物体变形反走样

基于参数曲线和曲面控制的空间变形是重要的几何外形编辑和柔性物体动画实现手段．当这两类变形方法的对象是多边形物体时,如何对变形物体进行重采样以得到高质量结果,是计算机动画和几何造型领域中的一个重要问题．该文针对B-样条曲线和曲面控制的空间变形方法,提出了面向多边形物体的空间变形反走样方法．在该方法中,利用等距技术将B-样条曲线或曲面所张成的变形空间近似表示为张量积B-样条参数体,结合作者提出的多边形物体精确B-样条自由变形方法,实现了参数曲线和曲面控制的多边形物体变形反走样．     

Fast evaluation of vector splines in three dimensions

Vector spline techniques have been developed as general-purpose methods for vector field reconstruction. However, such vector splines involve high computational complexity, which precludes applications of this technique to many problems using large data sets. In this paper, we develop a fast multipole method for the rapid evaluation of the vector spline in three dimensions. The algorithm depends on a tree-data structure and two hierarchical approximations: an upward multipole expansion approximation and a downward local Taylor series approximation. In comparison with the CPU time of direct calculation, which increases at a quadratic rate with the number of points, the presented fast algorithm achieves a higher speed in evaluation at a linear rate. The theoretical error bounds are derived to ensure that the fast method works well with a specific accuracy. Numerical simulations are performed in order to demonstrate the speed and the accuracy of the proposed fast method.     

Spline methods for a Birkhoff interpolation problem

In this paper, we study two new spline methods for the Birkhoff interpolation problem proposed in Costabile and Longo (Calcolo 47:49–63, 2010). Our methods are based on cubic spline and quintic spline respectively. The new methods are easy to be implemented. They are effective not only in approximating the original function but also in approximating its derivatives. The respective remainders and error bounds are given. Numerical tests are performed. Numerical results confirm the theoretical analysis and show that our methods are very practical.     

Non-polynomial sextic spline solution of singularly perturbed boundary-value problems

In this paper, we develop a generalized scheme based on non-polynomial sextic spline for the numerical solution of second-order singularly perturbed two-point boundary-value problems. The proposed method is second, fourth- and sixth-order accurate. Convergence analysis of the fourth-order method is briefly discussed. We show that the approximate solution obtained by the proposed method is better than existing spline methods. Numerical examples are given to illustrate the efficiency of our methods.     

Finite-difference technique based on exponential splines for the solution of obstacle problems

In this paper, we introduce a new technique based on cubic exponential spline functions for computing approximations to the solution of a system of fourth-order boundary value problems associated with obstacle, unilateral and contact problems. It is shown that the present method is of order two and four and gives approximations which are better than those produced by other collocation, finite difference and spline methods. Numerical evidence is presented to illustrate the applicability of the new methods.     

Numerische Lösung gewöhnlicher Differentialgleichungen mit Splinefunktionen

In this paper a general procedure to obtain spline approximations for the solutions of initial value problems for ordinary differential equations is presented. Several well-known spline approximation methods are included as special cases. It is common practice to partition the interval for which the initial value problem is defined into equidistant subintervals and to construct successively the spline approximation; thereby the spline function has to satisfy certain conditions at the knots. In the general procedure presented here additional knots are admitted in every subinterval. At these points which need not be equally spaced the spline approximation has to fulfill analogous conditions as at the original knots. Convergence and divergence theorems are proved; especially the influence of the additional knots on convergence and divergence of the method is investigated.     

Stability analysis for plates using the multivariable spline element method

The multivariable spline element method is used in this paper to solve the stability problems of plates and beams. The bicubic spline functions are employed to construct the bending moments, twisting moments and transverse displacements field. The spine eigenvalue equations with multiple variables are derived based on the Hellinger-Reissner mixed variational principle. Some numerical examples are given, the results are good agreement with other methods.     

An algorithm for constructing convexity and monotonicity-preserving splines in tension

In this paper we consider the problem of constructing an interpolatory spline in tension that matches the convexity and monotonicity properties of the data. In this connection, an algorithm is presented relying on the asymptotic properties of the splines in tension and making use of the generalized Newton-Raphson methods developed by Ben-Israel. The numerical performance of the proposed algorithm is tested and discussed for several data sets.     

有理多结点样条插值曲线及曲面

鉴于多结点样条曲线（MSIC）是一种点点通过的插值样条曲线,因此在多结点样条插值曲线研究的基础上,给出了有理多结点条插值曲线和有理多结点样条插值曲面的定义,并讨论了有理多结点样条的性质,对有理多结 样条曲线和有理多结点样条曲面的光滑拼接问题进行了讨论,此外,还对有理多结点样条在计算机辅助几何设计中的若干应用问题进行了说明。     

A class of methods based on a septic non-polynomial spline function for the solution of sixth-order two-point boundary value problems

Two new second- and fourth-order methods based on a septic non-polynomial spline function for the numerical solution of sixth-order two-point boundary value problems are presented. The spline function is used to derive some consistency relations for computing approximations to the solution of this problem. The proposed approach gives better approximations than existing polynomial spline and finite difference methods up to order four and has a lower computational cost. Convergence analysis of these two methods is discussed. Three numerical examples are included to illustrate the practical use of our methods as well as their accuracy compared with existing spline function methods.     

Motion estimation with quadtree splines

This paper presents a motion estimation algorithm based on a new multiresolution representation, the quadtree spline. This representation describes the motion field as a collection of smoothly connected patches of varying size, where the patch size is automatically adapted to the complexity of the underlying motion. The topology of the patches is determined by a quadtree data structure, and both split and merge techniques are developed for estimating this spatial subdivision. The quadtree spline is implemented using another novel representation, the adaptive hierarchical basis spline, and combines the advantages of adaptively-sized correlation windows with the speedups obtained with hierarchical basis preconditioners. Results are presented on some standard motion sequences     

Cubic spline curve fitting with controlled end conditions

Several approximate methods for cubic spline curve fitting have been developed and successfully used. This paper presents a more flexible version of a proven technique by using a set of end conditions suggested by Nutbourne. The advantages and disadvantages of several techniques are clarified and sample graphical output is given. The results should be of greatest interest to users of inexpensive, computer graphics equipment who are interested in improving passive graphical output.