共查询到19条相似文献,搜索用时 734 毫秒
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基于线元几何的旋转面点云数据旋转轴提取算法 总被引:2,自引:0,他引:2
当前逆向工程CAD建模技术中,由于基于特征的曲面重构技术在精确表达原始模型、还原设计意图以及快速建模中所具备的优势,使其逐渐成为逆向工程领域新的研究热点.为实现海量数据快速特征提取,提出了一种基于线元几何、线性丛的旋转面点云数据旋转轴提取算法.算法首先将三维空间中的点投影到线元空间中,构建线性丛,而后在线性丛上拟合运动方程,通过特征参数计算旋转轴位置.此方法无须精确估算曲面法矢,有效地提高了特征提取速度.在算法中设计并使用了K-Local-RANSAC算法进行快速离散区域扩张并排除外点,保证了算法的健壮性.实验证明,本算法对于包括圆环面在内的旋转面都能得到较好的效果,而且能较好地适用于碎片数据及含有噪声的情况. 相似文献
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三角网格模型的特征线提取 总被引:19,自引:5,他引:19
在反求工程中,散乱数据点云的曲面重构常采用三角网格模型,若将其转换成曲面实体模型则有更广泛的应用,从三角网格模型中提取特征线是转换过程中的重要步骤.在讨论反求工程中数据点云分块方法的基础上,采取“基于边”的方法来提取特征线:先提取特征点,再连接成特征线.根据相邻三角片的法矢夹角和各点主曲率是否为极值,分两次提取特征点,利用三角顶点加权和均匀化等方法减少狭长三角片对特征点提取的计算误差影响,再将特征点分组连接成B样条曲线.文中算法的结果可为B样条曲面分片拟合和建立B-rep曲面实体模型提供依据。 相似文献
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点云中提取的特征线在点云处理中具有重要的应用价值,已被应用于对称性检测、表面重建及点云与图像之间的注册等。然而,已有的点云特征线提取算法无法有效地处理点云中不可避免的噪声、外点和数据缺失,而随机采样一致性RANSAC由于具有较高的鲁棒性,在图像和三维模型处理中具有广泛的应用。为此,针对由建筑物或机械部件等具有平面特征的物体扫描得到的点云,提出了一种基于RANSAC的特征线提取算法。本算法首先基于RANSAC在点云中检测出多个平面,然后将每个平面参数化域的边界点作为候选,在这些候选点上再应用基于全局约束的RANSAC得到最终的特征线。实验结果表明,该算法对点云中的噪声、外点和数据缺失具有很强的鲁棒性。 相似文献
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三维散乱点云快速曲面重建算法 总被引:1,自引:0,他引:1
提出了一种基于Delaunay三角剖分的三维散乱点云快速曲面重建算法。算法首先计算点云的Delaunay三角剖分, 从Delaunay四面体提取初始三角网格, 根据Voronoi体元的特征构造优先队列并生成种子三角网格, 然后通过区域生长的方式进行流形提取。实验结果表明, 该算法可以高效、稳定地重构具有复杂拓扑结构、非封闭曲面甚至是非均匀采样的点云数据。与传统的基于Delaunay的方法比较, 该算法仅需要进行一次Delaunay三角剖分, 无须极点的计算, 因此算法的重构速度快。 相似文献
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《计算机辅助设计与图形学学报》2017,(4)
由LiDAR点云数据准确提取建筑物顶面是实现三维建筑模型自动重建的关键步骤.在分析现有顶面提取方法的基础上,提出一种渐进地提取LiDAR点云数据中精细建筑物顶面的方法.先以法向阈值和曲率阈值为约束,借助区域生长算法对原始点云进行初步分割,并得到面积较大、边界特征较明显的初始顶面;再借助主元分析法估算每个初始顶面的平面方程,并以点到平面的距离为约束,利用基于距离的区域生长算法提取其对应的精确顶面;最后通过随机抽样一致性算法(RANSAC)迭代地提取剩余点云中的小顶面.实验表明,通过动态调整阈值和迭代步骤,能够从LiDAR数据中精确地提取出复杂建筑物的顶面. 相似文献
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《计算机辅助设计与图形学学报》2015,(12)
特征线对三维模型的表达和识别具有重要意义,提出了符号曲面变化度的概念,其具备同时表达曲面弯曲程度和凹凸类型的能力,可以作为曲面曲率的良好近似.在此基础上,提出了一种基于符号曲面变化度与特征分区的特征线提取算法.首先选取点云中符号曲面变化度绝对值大于一定阈值的点作为潜在特征点;然后将符号曲面变化度作为区域增长限定条件对潜在特征点进行分割,并在通过局部曲面重建确定区域边界点后,采用基于曲面变化度和距离加权的双边滤波算法迭代细化边界点,以确定特征点真实位置;最后通过建立特征点的最小生成树实现特征线连接.实验结果表明,该算法能很好地识别、分割点云中的特征点,提取到准确、完整的特征线. 相似文献
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发展型对流占优扩散方程的FD-SD法的后验误差估计及空间网格调节技术 总被引:4,自引:0,他引:4
0.引言 流线扩散法(streamline diffusion method,简称 SD法)是由Hughes和 Brooks在1980年前后提出的一种数值求解对流占优扩散问题的新型有限元算法.随后,Johnson和 Navert把SD法推广到发展型对流扩散问题.这一方法因其兼具良好的数值稳定性和高阶精度,近年来在理论与实践方面都得到了很大发展. 对于发展型对流扩散问题的SD法均采用时空有限元,即把时间、空间同等对待,这样做虽然使关于时间、空间的精度很好地统一起来,但与传统的有限元相比,由于维数增加,计… 相似文献
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This article proposes a method of positive solution of a newly developed five-strut parallel machine with joint rings. The
key of this method is to find a mechanic principle contained in the structure. That is, the panels in which each strut locates
intersect in a single line, which is the axis line of the principal axis (active platform). According to this principle, a
mathematical geometric model is set up and an equation of positive solution is got through the principle of two panels intersecting
in one line. This method is different from early developed ones which are based on a non-linear equation set. In this article,
we set up a one-to-one correspondent relation among the structure parameters, the attitudes of strut and the attitudes of
spindle in space. Thus we get a unique, simple, accurate and temporarily effective positive solution. This positive solution
is also usable to other structures of parallel machine with joint rings, which have different degrees of freedom. In this
paper, the information of the attitudes of stretching struts is utilized during the process of positive solution in order
to prevent multi-solution. This methodology could be a common reference for other positive solutions of parallel machines. 相似文献
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本文提出了一种基于二次等参单元的等值线图生成算法,该算法根据有限元法将整个区域分割成多个互相连续的二次等参单元,通过生成每个等参单元内的等值线,进而生成整个区域内的等值线。 相似文献
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研制了一种新型的基于激光结构光三维视觉技术的移动机器人模块化测距雷达样机,并提出了多平面靶标的转轴现场标定方案,为实现其对周围环境的扫描测量,首先标定线激光器与网络摄像头的相对位置,利用三角法测量激光交线到摄像头光心的距离。然后标定舵机转轴与摄像机的相对位置,并将旋转的激光交线坐标,统一到一个世界坐标系下,实现扫描测距。三维测量实验中,相对误差0.31%,系统测量误差小于4%。实验证明该样机测量精度高,成本低,具有广阔的应用前景。 相似文献
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This paper presents a symmetric isoparametric finite element formulation for the inverse problem of aquifer transmissivity calculation with known piezometric head. An important aspect of the present formulation is that the groundwater flow equation describing the aquifer behavior is transformed into a second-order differential equation by introducing an artificial variable φ. The two-dimensional, line and transition elements derived based on the weak formulation of this transformed equation possess symmetric matrices. In the formulation of the line elements φ and its derivative in η direction are retained as primary variables. This permits modelling of sudden changes in aquifer width. The transition elements provide a natural connecting link between the two-dimensional elements and the line elements. The line elements provide an efficient means of modelling aquifers with unidirectional flow. Numerical examples are given. A comparison of the results obtained here with the Galerkin finite element solution (nonsymmetric formulation) clearly demonstrates the superiority of the formulation presented here. 相似文献
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In this paper, we study stabilization for a Schoedinger equation, which is interconnected with a heat equation via boundary coupling. A direct boundary feedback control is adopted. By a detailed spectral analysis, it is found that there are two branches of eigenvalues: one is along the negative real axis, and the other is approaching to a vertical line, which is parallel to the imagine axis. Moreover, it is shown that there is a set of generalized eigenfunctions, which forms a Riesz basis for the energy state space. Finally, the spectrum-determined growth condition is held and the exponential stability of the system is then concluded. 相似文献
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In this paper, a Galerkin finite element scheme to approximate the time–space fractional diffusion equation is studied. Firstly, the fractional diffusion equation is transformed into a fractional Volterra integro-differential equation. And a second-order fractional trapezoidal formula is used to approach the time fractional integral. Then a Galerkin finite element method is introduced in space direction, where the semi-discretization scheme and fully discrete scheme are given separately. The stability analysis of semi-discretization scheme is discussed in detail. Furthermore, convergence analysis of semi-discretization scheme and fully discrete scheme are given in details. Finally, two numerical examples are displayed to demonstrate the effectiveness of the proposed method. 相似文献