两类新的广义Ball曲线曲面的求值算法及其应用

本文研究两类新的广义Ball曲线曲面的求值算法及其应用.其一是把Bezier曲线曲面的求值转换到这两类曲线曲面的求值,大大加快了计算速度.其二是给出Bezier曲线与这两类广义Ball曲线的统一表示,并利用这种表示给出它们之间相互转换的递归算法.     

UNIFYING REPRESENTATION OF BEZIERCURVE AND GENERALIZED BALL CURVES

Abstract. This paper presents two new families of the generalized Ball curves which include theI~zier curve, the generalized Ball curves defined by Wang and Said independently and some in-termediate curves. The relative degree elevation and reduction schemes, recursive algorithmsand the Bernstein-Bezier representation are also given.     

两类新的广义Ball曲线

本文提出两类新的广义Ｂａｌｌ曲线,一类介于Ｗａｎｇ（王国瑾）和Ｓａｉｄ广义Ｂａｌｌ曲线之间,另一类介于Ｂｅｚｉｅｒ和Ｓａｉｄ曲线之间,同时给出有关的升阶公式、递推算法及转化成Ｂｅｚｉｅｒ形式的系数公式。     

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.     

与给定多边形相切的可调广义Ball闭曲线

讨论了与给定控制多边形相切的分段三次、五次和六次可调广义Ball曲线的构造方法,所构造的曲线分别是C1,C2和C3连续的,而且对切线多边形是保形的.曲线上的所有广义Ball曲线段的控制点由切线多边形的顶点直接计算产生.给出了在保持公共连接点处相应连续的情况下,内控制点的活动范围.曲线可以在一定范围内做局部修改.计算实例...     

基于广义逆矩阵的Ball曲线的降多阶逼近

给出了Ball曲线的一种降多阶逼近方法.将曲线的降多阶过程视为升阶的逆过程,利用广义逆矩阵的理论从而得到降阶曲线控制顶点的显式表示式.这种方法还考虑了原曲线与降阶曲线在两端点处分别达到(r,s)阶连续的情形(r≥0,s≥0).其次,给出了降阶误差界的估计.最后,给出数值例子.     

The dual bases for the Bézier-Said-Wang type generalized Ball polynomial bases and their applications

A unifying representation for the existing generalized Ball bases and the Bernstein bases are given. Then the dual bases for the Bézier-Said-Wang type generalized bases (BSWGB for short) are presented. The Marsden identity and the mutual transformation formulas between Bézier curve and Bézier-Said-Wang type generalized curve (BSWGB curve) are also given. These results are very useful for the applications of BSWGB curves and their popularization in CAGD. Numerical examples are also given to show the effectiveness of our methods.     

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.     

与给定多边形相切的C2和C3 广义 Ball闭曲线

B样条曲线和Bezier曲线在CAD、CAGD及逼近中非常有用,例如,在服装CAD纸样的设计过程中,通常先根据尺寸要求确定控制点,再根据控制点用直线段绘制样片的大体轮廓,即绘制多边形,在多边形内用直线和曲线绘制封闭的图形,由于样片的形状不规则,即构成样片的曲线比较复杂,为了使曲线光滑、丰满、有弹性,经常遇到曲线与控制多边形相切     

Ball基函数的对偶基及其应用

1．引言对于平面或空间上给定的n＋1个点vo，yi，…，v。，熟知的n次Bezier曲线定义为称为n次BernsteiN基函数，vo，yi，…；vn为Bezier曲线的控制点．在Ball开发的英国飞机公司Consurf外形设计系统中，他首先给出了三次Ball基函数的定义l‘，‘］．后来，Goodman和Said定义了［0，1］上Zm＋1次Ball基函数［5］一类似于B6zier曲线，称为［0，1］上关于控制点10，yi，…，vZ。＋1的B。11曲线·类似于B6zier曲线，Ball曲线也具有变差缩减、保凸等良好性质［3］，故在几何外形设计中也有着广泛的应用．熟知的B6zier曲线可由deCasteljan…     

圆弧和球面上的广义Ball多项式

本文以Ｂéｚｉｅｒ多项式理论为基础,引进了圆弧上的广义Ｂａｌ曲线及球面三角剖分上的广义Ｂａｌ曲面及其递归算法．     

三角域上Said-Bézier型广义Ball基的对偶泛函及其应用

A family of Said-Bézier type generalized Ball(SBGB) bases and surfaces with a parameter H over triangular domain is introducermediate 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.     

Intersections of Hugoniot curves with the sonic surface in the wave manifold

Local 1-shock curve arcs and local reverse 2-shock curve arcs were constructed, in the geometric context of the wave manifold, in a previous paper. In that geometric context, sonic and sonic’ surfaces are the boundaries of admissible shock curve arcs; in order to introduce the concept of non-local 1-shock curve arcs and non-local reverse 2-shock curve arcs it is necessary to understand how a hugoniot curve intersects the sonic and sonic’ surfaces; intersections of such curves with sonic’ surface are well known. In this paper we present a complete study on how Hugoniot curves intersect the sonic surface for a quadratic system of two conservation laws.     

On a Class of Generalized Curve Flows for Planar Convex Curves

In this paper, the authors consider a class of generalized curve flow for convex curves in the plane. They show that either the maximal existence time of the flow is finite and the evolving curve collapses to a round point with the enclosed area of the evolving curve tending to zero, i.e., limt→T A(t) = 0, or the maximal time is infinite, that is, the flow is a global one. In the case that the maximal existence time of the flow is finite, they also obtain a convergence theorem for rescaled curves at the maximal time.     

带形状参数的代数三角样条曲线曲面的构造（英文）

The construction of trigonometric B-spline curves with shape parameters has become the hotspot in computer aided geometric design.However,the shape parameters of the curves and surfaces are all global parameters and only meet with C~2 continuity in some previous papers.In order to provide more flexible approaches for designers,the algebraic and trigonometric spline(AT-spline) curves and surfaces are constructed as a generalization of the traditional cubic uniform B-spline curves and surfaces.AT-spline curves and surfaces not only inherit the properties of trigonometric B-spline curves,but also exhibit better performance when adjusting its local shapes through two shape parameters.Particularly,the AT-spline rotational surfaces with two local shape parameters are presented.When the shape parameters take special value,it can accurately represent the conic curve and surface.     

Said型广义Ball基函数的拓展

在本文中,我们给出了构造Said型广义Ball基函数的新方法,该方法的优点在于,既可以推出奇次多项式的Said型广义Ball基函数表示,也可以推出偶次多项式的Said型广义Ball基函数表示;该方法的另一优点是,能很自然地定义Said型广义Ball基函数的对偶泛函; 给出了Said型广义Ball基函数的积分性质;定义了一种新的基函数, Said型广义Ball基函数是其特例; 给出了这种新的基函数的对偶泛函和类Marsden恒等式.     

基于几何连续的AT-β-Spline曲线曲面的构造

为了更好地修改给定的样条曲线曲面,构造了满足几何连续的带两类形状参数的代数三角多项式样条曲线曲面,简称为AT-β-Spline.这种代数三角曲线曲面不仅具有普通三角多项式的性质,而且具有全局的和局部的形状可调性.同时还具备较为灵活的连续性.当两类形状参数在给定的范围内任意取值时,这种带两类形状参数的AT-β-Spline曲线满足一阶几何连续性;如果给定两段相邻曲线段中的两类形状参数满足-1≤α≤1,μ_i=λ_(i+1)或μ_i=λ_i=μ_(i+1)=λ_(i+1)时,则带两类形状参数的AT-β-Spline曲线满足C~1∩G~2连续.另外利用奇异混合的思想,构造了满足C~1∩G~2插值AT-β-Spline曲线,解决曲线反求的几何连续性等问题.同时还给出了旋转面的构造,描述了两类形状参数对旋转面的几何外形的影响;当形状参数取特殊值时,这种AT-β-Spline曲线曲面可以精确地表示圆锥曲线曲面.从实验的结果来看,本文构造的AT-β-Spline曲线曲面是实用的有效的.     

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.     

On the generalized Ball bases

The Ball basis was introduced for cubic polynomials by Ball, and two different generalizations for higher degree m polynomials have been called the Said–Ball and the Wang–Ball basis, respectively. In this paper, we analyze some shape preserving and stability properties of these bases. We prove that the Wang–Ball basis is strictly monotonicity preserving for all m. However, it is not geometrically convexity preserving and is not totally positive for m>3, in contrast with the Said–Ball basis. We prove that the Said–Ball basis is better conditioned than the Wang–Ball basis and we include a stable conversion between both generalized Ball bases. The Wang–Ball basis has an evaluation algorithm with linear complexity. We perform an error analysis of the evaluation algorithms of both bases and compare them with other algorithms for polynomial evaluation.     

Patchworking singular algebraic curves II

In this paper we present various particular versions of the general patch-working procedurefor the construction of reduced algebraic curves with prescribed singularities, on algebraic surfaces. Among the main examples are a deformation of reducible algebraic curves on reducible algebraic surfaces in the presence of non-transverse intersections of a curve with the singular locus of a surface, and a deformation of curves with multiple components. As an application we deduce, a significant asymptotical improvement for the sufficient existence criterion of algebraic curves with arbitrary prescribed singlarities in given linear systems on smooth projective algebraic surfaces. Both authors were partially supported by the Herman Minkowsky-Minerva Center for Geometry at Tel Aviv University, and by grant no. G-616-15.6/99 from the German-Israeli Foundation for Research and Development. The first author was also supported by the Bessel Research Award from the Alexander von Humboldt Foundation.