广义Ball曲线的包络定理

Ｂｅｚｉｅｒ曲线和Ｂ样条曲线的包络性已在文［４］中讨论过，本文研讨广义Ｂａｌｌ曲线的包络性。     

广义Ball样条曲线及三角域上曲面的升阶公式和转换算法

Ｔ．Ｎ．Ｔ．Ｇｏｏｄｍａｎ在［９］和［１０］中给出了广义Ｂａｌｌ样条曲线、曲面的奇次升阶公式和有关性质，但未给出偶次广义Ｂａｌｌ样条形式。     

由控制多边形内部两点确定的三次有理Bézier曲线

１．引言主要应用于自由曲线设计的有理Ｂｅｚｉｅｒ曲线在ＣＡＧＤ中起了重要作用．有理Ｂｅｚｉｅｒ曲线的几何形状不仅受其控制多边形而且受其权因子的控制,有关这方面的研究正受到越来越多的关注,例如［１－７］．当控制多边形给定时,权因子为有理Ｂｅｚｉｅｒ曲线的形状控制提供了自由度．权因子的性质及其与有理Ｂｅｚｉｅｒ曲线形状的关系较为复杂,目前尚未得到全面研究·文［４,５］给出了当修改有理Ｂｅｚｉｅｒ曲线上的一点时,权因子的计算公式,但该公式不能用于同时修改曲线上两点的情况,从而限制了修改曲线的灵活性．文…     

参数五次GC^2 Hermite插值

本文研究几何Ｈｅｒｍｉｔｅ插值问题,对于给定的切矢和曲率,导出了一条分段五次Ｂｅｚｉｅｒ插值曲线。该曲线的所有Ｂｅｚｉｅｒ点由已知的曲率、切矢和型值点直接计算生成,曲线是ＧＣ＾２连续的和局部的。最后,给出了一个数值实例。     

Bezier曲线的矩阵形式及其应用

本文给出了Ｂｅｚｉｅｒ曲线的矩阵形式及其某些应用     

关于“有理Bezier曲线面中权因子的性质研究”一文的注记”

关于“有理Ｂｅｚｉｅｒ曲线面中权因子的性质研究”一文的注记”齐从谦，邬弘毅（安徽工学院）ＡＲＥＭＡＲＫＯＮ＂ＡＮＩＮＶＥＳＴＩＧＡＴＩＯＮＯＦＴＨＥＷＥＩＧＨＴＳＩＮＲＡＴＩＯＮＡＬＢＥＺＩＥＲＣＵＲＶＥＳ／ＳＵＲＦＡＣＥＳ＂￥ＱｉＣｏｎｇ－ｑｉａｎ...     

广义Bézier曲线与曲面在连接中的应用

通常的贝齐尔（Ｂｅｚｉｅｒ）曲线、曲面，在其端点或边界只具有ＧＣ１阶插值性．本文在保持通常贝齐尔曲线、曲面性质的基础上，定义了一种广义的贝齐尔曲线、曲面，使其在曲线段的端点和曲面片的边界具有高阶光滑插值性，它可方便地光滑连接两条参数型的曲线段和两张以上参数型曲面片，并且连接方式是ＧＣｒ（ｒ≥１）的．所以广义贝齐尔曲线、曲面在计算机辅助设计应用中更具有独特的意义．     

CONSURF系统中机身造型曲线的若干几何性质

本文用计算几何学的观点对Ａ．Ａ．Ｂａｌｌ在前英车航空公司研制成功的ＣＯＮＳＵＲＦ系统进行分析，证明了这一系统的机身造型曲线具有包络性质，分段性质，变差缩减性质，奇点拐点分布性质和保凸性质。     

任意次有理Bezier曲线／面对其控制多边形／网格的整体或局部逼近

本文给出一种利用权因子构造整体或局部逼近控制多边形／网格的有理Ｂｅｚｉｅｒ曲线／面的方法,该法适用于任意次数的有理Ｂｅｚｉｅｒ曲线／面、任意的控制多边形／网络,权因子的选择和逼近度的估计都只依赖于一个参数ｗ．当ｗ→＋∞时,相应的曲线／面可按预定要求整体或局部地逼近其控制多边形／网络,逼近阶为ｏ（１／ｗ）。     

增长曲线模型回归系数的广义岭估计

本文采用广义岭估计β（Ｋ）来估计增长曲线模型中回归系数β＝ｖｅｃ（Ｂ），通过Ｋ值的选取，可使其均方误差（ＭＳＥ）小于ＬＳ估计β的ＭＳＥ。同时对ＬＳ估计的任一线性变换，给出了其均方误差的一个无偏估计，并应用极小化β（Ｋ）的ＭＳＥ的无偏估计的方法，得到了确定岭参数的公式。     

Rational cubic/quartic Said-Ball conics

In CAGD, the Said-Ball representation for a polynomial curve has two advantages over the Bézier representation, since the degrees of Said-Ball basis are distributed in a step type. One advantage is that the recursive algorithm of Said-Ball curve for evaluating a polynomial curve runs twice as fast as the de Casteljau algorithm of Bézier curve. Another is that the operations of degree elevation and reduction for a polynomial curve in Said-Ball form are simpler and faster than in Bézier form. However, Said-Ball curve can not exactly represent conics which are usually used in aircraft and machine element design. To further extend the utilization of Said-Ball curve, this paper deduces the representation theory of rational cubic and quartic Said-Ball conics, according to the necessary and sufficient conditions for conic representation in rational low degree Bézier form and the transformation formula from Bernstein basis to Said-Ball basis. The results include the judging method for whether a rational quartic Said-Ball curve is a conic section and design method for presenting a given conic section in rational quartic Said-Ball form. Many experimental curves are given for confirming that our approaches are correct and effective.     

ANOTHER TYPE OF GENERALIZED BALL CURVES AND SURFACES

In 2000,Wu presented two new types of generalized Ball curves,one of which is called an NB1 curve located between the Wang Ball curve and the Said Ball curve.In this article,the authors aim to discuss properties of NB1 curves and surfaces,including the recursive algorithms,conversion algorithms between NB1 and Bézier curves and surfaces, etc.In addition the authors compare the computation efficiency of recursive algorithms for the NB1 and above mentioned two generalized Ball curves and surfaces.     

Dual Bases for a New Family of Generalized Ball Bases

This paper presents the dual bases for a new family of generalized Ball curves with a position parameter K, which includes the Bezier curve, generalized Said-Ball curve and some intermediate curves. Using the dual bases, the relative Marsden identity, conversion formulas of bases and control points of various curves are obtained.     

基于最小二乘法的张量积Said-Ball曲面降多阶逼近

给出张量积Said-Ball曲面降多阶逼近的一种方法.该方法根据原张量积Said-Ball曲面Pn,m(u,v)与降多阶张量积Said-Ball曲面Qn1,m1(u,v)(n1≤n-1,m1≤m-1)在最小二乘范数下的距离函数在单位正方形[0,1]×[0,1]上取最小值,从而得到了用矩阵表示的降多阶张量积Said-Ball曲面Qn1,m1(u,v)的控制顶点{qij}in1=,0,m1j=0的显示表示式.在降多阶过程中,分别考虑了带角点高阶插值条件和不带角点插值条件的情形.文末附有数值例子,并将本文方法与参考文献(9)的方法做了比较.     

The Dual Functionals for the Generalized Ball Basis of Wang-Said Type and Basis Transformation Formulas

The generalized Ball curves of Wang-Said type with a position parameter L not only unify the Wang-Ball curves and the Said-Ball curves, but also include several useful intermediate curves. This paper presents the dual functionals for the generalized Ball basis of Wang-Said type. The relevant basis transformation formulae are also worked out.     

DUAL FUNCTIONALS OF SAID-BEZIER TYPE GENERALIZED BALL BASES OVER TRIANGLE DOMAIN AND THEIR APPLICATION

A family of Said-Bézier type generalized Ball (SBGB) bases and surfaces with a parameter H over triangular domain is introduced, which unifies Bézier surface and Said-Ball surface and includes several intermediate surfaces. To convert different bases and surfaces, the dual functionals of bases are presented. As an application of dual functionals, the subdivision formulas for surfaces are established.     

Accurate computations with Said-Ball-Vandermonde matrices

A generalization of the Vandermonde matrices which arise when the power basis is replaced by the Said-Ball basis is considered. When the nodes are inside the interval (0,1), then those matrices are strictly totally positive. An algorithm for computing the bidiagonal decomposition of those Said-Ball-Vandermonde matrices is presented, which allows us to use known algorithms for totally positive matrices represented by their bidiagonal decomposition. The algorithm is shown to be fast and to guarantee high relative accuracy. Some numerical experiments which illustrate the good behaviour of the algorithm are included.     

Total positivity and accurate computations with Gram matrices of Said-Ball bases

In this article, it is proved that Gram matrices of totally positive bases of the space of polynomials of a given degree on a compact interval are totally positive. Conditions to guarantee computations to high relative accuracy with those matrices are also obtained. Furthermore, a fast and accurate algorithm to compute the bidiagonal factorization of Gram matrices of the Said-Ball bases is obtained and used to compute to high relative accuracy their singular values and inverses, as well as the solution of some linear systems associated with these matrices. Numerical examples are included.     

Computing the minimum distance between two Bézier curves

A sweeping sphere clipping method is presented for computing the minimum distance between two Bézier curves. The sweeping sphere is constructed by rolling a sphere with its center point along a curve. The initial radius of the sweeping sphere can be set as the minimum distance between an end point and the other curve. The nearest point on a curve must be contained in the sweeping sphere along the other curve, and all of the parts outside the sweeping sphere can be eliminated. A simple sufficient condition when the nearest point is one of the two end points of a curve is provided, which turns the curve/curve case into a point/curve case and leads to higher efficiency. Examples are shown to illustrate efficiency and robustness of the new method.     

On evolutoids of planar convex curves

There are many interesting curves which we can associate with a given convex curve, however, in this work we are especially interested in studying the relations between the given curve and its evolutoids: that is, the curve obtained as the envelope of lines making a fixed angle with the normal line at every point of the curve. The first result is an inequality between the area enclosed by the given curve and the area enclosed by its evolutoid. Also, we proved that a convex curve is of constant width (centrally symmetric) if and only if its evolutoid for a fixed angle is of constant width (centrally symmetric).