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1.
MO Guo-liang ZHAO Ya-nan 《浙江大学学报(A卷英文版)》2006,7(12):2043-2049
INTRODUCTION B-spline curves and surfaces have been widely used in Computer Graphics (CG) and Computer Aided Design (CAD) (Hoschek and Lasser, 1993; Piegl and Tiller, 1997). Many practical algorithms, such as those for position and derivatives evaluation, knot insertion, knot deletion and degree elevation, are usually implemented in a CAD system that uses B-spline as a shape design tool. In curve and surface design, a given B-spline curve or surface usually needs to be extended in … 相似文献
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建模是三维制作的基础.NURBS曲线建模是目前比较流行的建模方式,它能产生平滑连续的曲面,使用数学函数来定义曲线和曲面,可在不改变外形的前提下自由控制曲面的精细程度.本文结合具体实例,阐释NURBS建模技术的主要思路及其流程. 相似文献
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利用奇异混合函数将双三次B样条曲面与虚拟曲面片作混合,构造一类可插值给定数据点的插值曲面,该类曲面在边界处可达到C~2连续,参数α可对曲面片整体形状进行调控。进一步,构造了可局部调控形状的带形状参数的插值曲面。 相似文献
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CHENG Si-yuan ZHANG Xiang-wei HUANG Man-hui 《重庆大学学报(英文版)》2005,4(4):185-188
1 Introduction a Planar curve approximation is a crucial issue in many applications of computer graphics, computer vision, CAD/CAM, image processing, etc., and there have been many reports in the literature on solving the curve approximation problem by using the B-splines. However, most of the existing methods required parameterization of data points on the target curve. It is a difficult task to estimate these parameters and different parameter choices may largely affect the approximation … 相似文献
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Catmull-Clark细分曲面能量精确分析方法 总被引：3，自引：0，他引：3
提出了一种新的精确计算包含奇异顶点的Catmull-Clark细分曲面能量的方法.通过把Catmull-Clark细分曲面片转化成双3次B样条曲面片,导出了任意拓扑结构的细分曲面完整的能量计算公式.该方法不需要对细分曲面进行递归细分,就能计算出细分曲面的膜能量和薄板能量,与现有方法相比,该方法能快速准确地计算出细分曲面的能量.曲面光顺实例表明,用该方法计算细分曲面能量高效可行. 相似文献
6.
丁茹 《天津工程师范学院学报》2004,14(4):30-32
对NURBS(非均匀有理B样条)曲面的拟合算法和利用"权值"局部修改NURBS曲面的方法进行了研究,运用OpenGL技术实现了NURBS曲面的虚拟显示,通过血管的表面重建实验,验证了NURBS曲面拟合算法的正确性。 相似文献
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曲面重构是逆向工程的核心内容,目前大多数曲线曲面的研究都是围绕NURBS数学模型展开的。以NURBS数学模型为基础,对曲线曲面重构的方法、步骤、及其常见问题的分析处理进行了研究讨论,提出了曲线与点云相互结合重构曲面的方法,并进行了无动力排风扇叶片曲面的重构。结果表明,提出的方法是有效的和可行的,且具有一定的工程实用价值。 相似文献
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This paper presents an approach for recognizing both isolated and intersecting geometric features of freeform surface models of parts, for the purpose of automating the process planning of sheet metal forming. The developed methodology has three major steps： subdivision of B-spline surfaces, detection of protrusions and depressions, and recognition of geometric features for sheet metal forming domain. The input geometry data format of the part is based on an IGES CAD surface model represented in the form of trimmed B-spline surfaces. Each surface is classified or subdivided into different curvature regions with the aid of curvature property surfaces obtained by using symbolic computation of B-spline surfaces. Those regions satisfying a particular geometry and topology relation are recognized as protrusion and depression （DP） shapes. The DP shapes are then classified into different geometric features using a rule-based approach. A verified feasibility study of the developed method is also presented. 相似文献
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对非均匀有理B样条(NURBS)参数化特征设计和隐式代数曲面的原理实现曲面造型进行了介绍。在仿真的过程中运用CAD/CAM技术软件实现了凉亭顶部的设计,证实了在软件中运用非均匀有理B样条(NURBS)参数化特征设计在曲面造型方面是可行的,不仅拟合度好而且可以提高设计效率,并且可以使得图形更严密。 相似文献
11.
A family of quasi-cubic blended splines and applications 总被引：4，自引：0，他引：4
SU Ben-yue TAN Jie-qing 《浙江大学学报(A卷英文版)》2006,7(9):1550-1560
INTRODUCTION Bézier curves and uniform B-spline curves are powerful tools for constructing free form curves and surfaces (FFC/FFS). But they cannot represent the arcs, hyperbola, sphere, cylinders and other transcendental curves and surfaces exactly. In order to avoid the in- conveniences, many bases are presented in other new spaces (Zhang, 1996; Pe?a, 1997; Walz, 1997; Sánchez-Reyes, 1998; Mainar et al., 2001). Note that, these existing methods can deal with both polynomial curve… 相似文献
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Curve and surface blending is an important operation in CAD systems, in which a non-uniform rational B-spline （NURBS） has been used as the de facto standard. In local comer blending, two curves intersecting at that comer are first made disjoint, and then the third blending curve is added-in to smoothly join the two curves with G^1- or G^2-continuity. In this paper we present a study to solve the joint problem based on curve extension. The following nice properties of this extension algorithm are exploited in depth： （1） The parameterization of the original shapes does not change; （2） No additional fragments are created. Various examples are presented to demonstrate that our solution is simple and efficient. 相似文献
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Due to the complex nature of multi-source geological data, it is difficult to rebuild every geological struc-ture through a single 3D modeling method. The multi-source data interpretation method put forward in this analysis is based on a database-driven pattern and focuses on the discrete and irregular features of geological data. The geological data from a variety of sources covering a range of accuracy, resolution, quantity and quality are classified and inte-grated according to their reliability and consistency for 3D modeling. The new interpolation-approximation fitting construction algorithm of geological surfaces with the non-uniform rational B-spline （NURBS） technique is then pre-sented. The NURBS technique can retain the balance among the requirements for accuracy, surface continuity and data storage of geological structures. Finally, four alternative 3D modeling approaches are demonstrated with reference to some examples, which are selected according to the data quantity and accuracy specification. The proposed approaches offer flexible modeling patterns for different practical engineering demands. 相似文献
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The representation method of heterogeneous material information is one of the key technologies of het-erogeneous object modeling, but almost all the existing methods cannot represent non-uniform rational B-spline (NURBS) entity. According to the characteristics of NURBS, a novel data structure, named NURBS material data structure, is proposed, in which the geometrical coordinates, weights and material coordinates of NURBS heterogeneous objects can be represented simultaneously. Based on this data structure, both direct representation method and inverse construction method of heterogeneous NURBS objects are introduced. In the direct representation method, three forms of NURBS heterogeneous objects are introduced by giving the geometry and material information of control points, among which the homogeneous coordinates form is employed for its brevity and easy programming. In the inverse construction method, continuous heterogeneous curves and surfaces can be obtained by interpolating discrete points and curves with specified material information. Some examples are given to show the effectiveness of the proposed methods. 相似文献
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针对含自由曲面及标准解析曲面零件加工精度的高精度检测,本文提出一种形状公差评定的新方法——面向CAD模型的曲面形状误差检验。它实现了各种标准解析曲面和自由曲面形状的高精度检测,采用表达式精确地表示各种标准解析曲面和自由曲面;利用数据库技术研究CMM测量点云和CAD模型的最佳匹配算法;比较测量点云和CAD模型的法向偏移量即曲面形状误差,且用图形直观地显示出来。最后进行计算机仿真实验,实例验证算法可行性。 相似文献
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曲面柔性制孔机器人末端执行器及其法向姿态调整的一种新算法(英文) 总被引：1，自引：0，他引：1
设计了一种曲面柔性制孔机器人末端执行器,并针对该末端执行器提出了一种法向姿态调整的新算法.空间不共面四点可以确定一个与之相切的球面,求出该球面的半径及球心位置,以该球面近似代表制孔点区域的曲面,联结制孔点与该球面球心的矢量即可近似代表制孔点曲面的法矢量.根据这一原理,该算法首先用4个位移传感器测量出曲面上制孔区域内4个点的坐标,并由此计算出制孔位置的法向矢量,然后计算出此法向矢量与末端执行器上电主轴的轴线矢量的误差.根据该误差,进一步计算出末端执行器上2个旋转轴的旋转角度及制孔机器人另外3个直线移动方向的移动距离,从而实现调整主轴在制孔点与曲面垂直的功能.针对2种类型曲面的仿真结果表明,根据该算法可以实现较高的调整精度和效率. 相似文献
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程少华 《周口师范学院学报》2006,23(2):35-37
根据二次非均匀B样条曲线矩阵表达式，对于任意曲线上的2n＋1个型值数据点，给出了一个仅仅利用这些型值数据，反算二次非均匀B样条曲线控制顶点的算法。 相似文献
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在分析车身外形曲面设计规律的基础上，从ＮＵＲＢＳ方法的原始定义出发推导了 具有实用意义的算法，并建立了用于车身外形曲面几何造型的ＣＡＧＤ系统，最后给出了 设计实例． 相似文献