共查询到17条相似文献,搜索用时 577 毫秒
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嵌入参数空间的曲面控制自由变形方法 总被引:5,自引:1,他引:5
提出了一种新的通过控制参数曲面来实现物体的自由变形的方法,物体通过映射函数被嵌入到曲面的参数空间从而实现变形,同时映射函数的引入增加了变形的控制手段。实验表明该方法具有易于交互和控制的优点,适用于几何造型和计算机动画领域。 相似文献
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基于曲线和曲面控制的多边形物体变形反走样 总被引:2,自引:0,他引:2
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. 相似文献
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将双参数四点细分曲线方法进行推广,提出了基于双参数四点细分法的曲面造型方法,并对其收敛性进行了分析。该方法通过对两个参数的适当调节能够较容易地控制极限曲面的形状,极限曲面能够达到C4连续,可以应用到对曲面的连续性要求较高的曲面造型中去。在给定初始数据的条件下,可通过对形状参数的适当选择来实现对极限曲面的形状调整和控制,试验表明该算法生成光滑曲面是有效的。 相似文献
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提出用推广B 样条细分曲面来混合多张曲面的方法,既适用于一般网格曲面,又适
用于推广B 样条参数曲面混合。根据需要选择阶数和张力参数,可全局调整整张混合曲面的形状。
中心点和谷点的计算都设置了形状参数,可局部调整混合部分形状。推导出二次曲面细分初始网
格计算公式,并将3 阶推广B 样条细分曲面混合方法用于多张二次曲面混合,与已有的二次曲面
混合方法相比具有明显的优势。 相似文献
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BBN曲面的形状分析与控制 总被引:2,自引:0,他引:2
研究了调节凸Bézier曲面、B-样条曲面及NURBS曲面(BBN曲面)一个控制点以后,曲面形状变化的规律.通过将BBN曲面分解成一张凸曲面与具有特殊形状曲面的叠加,建立了曲面变形前后一些几何量与变形位移量之间的数量关系,得到了凸BBN曲面失去凸性的充分条件和判据.相应的结果可应用于调节与控制BBN曲面形状的算法设计. 相似文献
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基于元球隐式曲面表示,提出一个对给定3维物体表面采样数据进行自动曲面重建的方法。首先由空间采样点获取它们的球逼近表示;然后使用这些球作为元球的初始估计,构造出一张初始的元球隐式曲面;最后通过一个能量优化过程调整每个元球的形状参数,得到最终的隐式曲面。球的位置与形状的有效估计和局部支撑的元球核函数的使用极大地加速了曲面优化过程。实验结果表明该方法是有效而实用的。 相似文献
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多边形物体的精确B-样条自由变形* 总被引:6,自引:0,他引:6
在计算机动画与几何造型中,自由变形是一种重要的几何形状修改方法.该文从移位算子和函数复合的观点探讨一种方法,即当被变形物体用三角片表示、变形工具为B-样条参数体时,变形后的物体可以精确地表示为一组三角Bzier曲面片,其次数为B-样条参数体3个方向的次数之和.此方法的核心在于自由变形是作用在三角片上,而不是顶点上,所以解决了多边形物体B-样条自由变形的点采样问题. 相似文献
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三角域上带形状参数的三次Bézier曲面 总被引:1,自引:0,他引:1
张量积Bézier曲面被成功地应用于商业CAD系统中,然而实际工程中的某些外形却无法依靠张量积形式实现.因此在CAGD中,三角Bézier曲面成为外部形状设计的主要工具之一.为了更加灵活地控制三角曲面的形状,构造了一组带形状参数的三次多项式基函数,它们是三角域上三次Bernstein基的扩展.利用该组基函数定义了三角域上带形状参数的多项式曲面.基函数和曲面分别具有Bernstein基和Bézier曲面的性质.在形状参数的取值范围内,三次Bézier三角曲面是它的特例.由于含有可调的形状参数,该曲面在形状修改与变形中具有更大的灵活性.形状参数具有明确的几何意义,参数越大曲面越逼近控制网格.实例表明,通过改变形状参数的取值可以调整曲面的形状,在CAGD中该方法是有效的. 相似文献
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Shape Modification and Deformation of Parametric Surfaces 总被引:2,自引:0,他引:2
A new method for shape modification or deformation of all kinds of parametric surfaces is presented. Instead of using any control mesh and designing any auxiliary tools for modification or deformation, this method only needs to multiply the equation of the original surface by several shape operator matrixes so that deformation effects are achieved. Due to introducing interactive control parameters with different properties those parameters can be changed to get more ideal effects of deformation or shape modification. The core of the method is that so-called cosine extension function is proposed by which the shape operator matrix can be created. Experiment shows that the method is simple, intuitive and easy to control, and diversified local deformations or shape modifications can easily be made via small and random variations of interactive control parameters. 相似文献
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Adrien Bernhardt Loic Barthe Marie‐Paule Cani Brian Wyvill 《Computer Graphics Forum》2010,29(2):367-375
Blending is both the strength and the weakness of functionally based implicit surfaces (such as F‐reps or soft‐objects). While it gives them the unique ability to smoothly merge into a single, arbitrary shape, it makes implicit modelling hard to control since implicit surfaces blend at a distance, in a way that heavily depends on the slope of the field functions that define them. This paper presents a novel, generic solution to blending of functionally‐based implicit surfaces: the insight is that to be intuitive and easy to control, blends should be located where two objects overlap, while enabling other parts of the objects to come as close to each other as desired without being deformed. Our solution relies on automatically defined blending regions around the intersection curves between two objects. Outside of these volumes, a clean union of the objects is computed thanks to a new operator that guarantees the smoothness of the resulting field function; meanwhile, a smooth blend is generated inside the blending regions. Parameters can automatically be tuned in order to prevent small objects from blurring out when blended into larger ones, and to generate a progressive blend when two animated objects come in contact. 相似文献
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为了改进参数曲面自由变形方法,构造了凸多边形域上的伸缩因子函数,它具有已往文献所引入的伸缩因子的特性。可使用新的伸缩因子去作用待变形曲面的参数方程,从而使曲面发生形变。可通过交互改变控制参数来控制曲面的形状,使其能够更好地表示一些不规则实体的外型。实验表明,该方法的数学背景简单、易于控制、重复使用可以达到获得丰富变形效果的目的。可用于几何造型、计算机动画以及CAD/CAM等领域。 相似文献
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Multiresolution free-form deformation with subdivision surface of arbitrary topology 总被引:1,自引:0,他引:1
Jieqing Feng Jin Shao Xiaogang Jin Qunsheng Peng A. Robin Forrest 《The Visual computer》2006,22(1):28-42
A new free-from deformation method is presented in this paper. Object deformation is controlled by a mesh of arbitrary topology,
namely a control mesh. The subdivision surface determined by the control mesh spans an intermediate deformation space. The
object is embedded into the space by the nearest point rule. When the shape of the control mesh is changed, the object embedded
in the intermediate deformation space will be deformed accordingly. Since the subdivision surface has a multiresolution property,
the proposed deformation method naturally has a multiresolution property. A technique for generating control meshes is also
introduced in the paper. Compared with previous deformation methods with arbitrary topology control tools, the proposed method
has the advantages of flexible control and computational efficiency. 相似文献
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Frédéric Truchetet 《计算机科学技术学报》2006,21(2):238-243
In the previous work, an efficient method has been proposed to represent solid objects as multiple combinations of globally deformed supershapes. In this paper, this framework is applied with a new supershape implicit function that is based on the notion of radial distance and results are presented on realistic models composed of hundreds of hierarchically globally deformed supershapes. An implicit equation with guaranteed differential properties is obtained by simple combinations of the primitives' implicit representations using R-function theory. The surface corresponding to the zero-set of the implicit equation is efficiently and directly polygonized using the primitives' parametric forms. Moreover, hierarchical global deformations are considered to increase the range of shapes that can be modeled. The potential of the approach is illustrated by representing complex models composed of several hundreds of primitives inspired from CAD models of mechanical parts. 相似文献
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Displaying objects with high accuracy is necessary for CAGD (computer-aided geometric design) and for the synthesis of photo-realistic images. Traditionally, polygonal approximation methods have been employed to display free-form surfaces. They bring on low accuracy of display not only in shape, but also in intensity of objects. In this paper, a scanline algorithm to directly display parametric surface patches, expressed by trimmed Bézier surfaces, without polygonal approximation is proposed. In the method proposed here, curved surfaces are subdivided into subpatches with curved edges intersecting with a scanline, and the intersections of every subpatch and the scanline are calculated. This method is extremely robust for calculating the intersections, which can be obtained with only a few iterations; the Bézier clipping method is used for the iteration. Anti-aliased images with shadows and texture mapping are given to show the effectiveness of the method proposed. 相似文献