三次Bézier曲线与圆弧有重合点时的Hausdorff距离

Hausdorff距离常用来度量两条曲线的匹配程度,因此,它可以用来度量三次Bézier曲线与圆弧之间的逼近程度。论文给出了三次Bézier曲线与圆弧在中点重合时,它们之间的Hausdorff距离表达式;以及三次Bézier曲线与圆弧在一般情况重合(除端点外)时的Hausdorff距离表达式。通过这些表达式可以直接得出三次Bézier曲线与圆弧之间的Hausdorff距离。     

一种改进的薄壁文物碎片特征轮廓线提取技术

针对使用一般的边界提取方法提取三维网格模型特征轮廓线不完整问题,提出一种新的薄壁文物碎片特征轮廓线提取的综合算法。区别了特征轮廓线和轮廓线的概念,引入主轮廓线和次轮廓线以及二级邻接生长曲面的概念。主轮廓线的提取使用改进的基于边重数判断的提取方法;提出次轮廓线的一种新的提取方法:首先对三维网格曲面分割并识别断裂面,然后对断裂面的二级邻接生长曲面进行曲面扫描,提取次轮廓线;最后从主轮廓线和次轮廓线中得到三维模型的特征轮廓线。使用该算法准确地提取了文物碎片的特征轮廓线,实验结果表明此方法稳定且准确。     

计算机输出曲线的割线段快速逼近法

采用割线段击逼近计算机输出的非线性曲线．文中分析了用割线段厦用弦线段逼近间的关系。自变量h和曲线及割(弦)线间距离d之间的关系。它指出在同样精度下弦线段数与割线段数之比是√2，当自变量步长h变成ah(a<1)时,割线与曲线的距离d将变成a^2d．文中给出了不含任何迭代的步长函数h(x)的计算公式。     

基于显著几何特征的文物碎片分类

采用传统的基于文物碎片形状特征的分类方法对外形受损的文物碎片准确率低下.有浮雕或者印记的文物表面存在一些规律性的显著几何特征,提取此类特征结构可更好地描述受损文物形状特征.提出一种基于显著几何特征的文物碎片分类方法.首先给出显著几何特征的定义并计算代表模型表面局部区域的局部表面描述符,然后通过对局部表面描述符聚类来提取兵马俑碎片表面的显著几何特征,最后运用EMD方法对显著几何特征进行匹配并确定分类.实验结果表明该方法对兵马俑碎片的分类具有较高的准确率.     

带自由曲面的三视图重建算法研究

针对蕴含自由曲面的三视图,提出了通过恢复边界线和轮廓线进而根据这些恢复的空间曲线重建自由曲面的算法。首先分析并证明了自由曲面在三视图中的投影性质,从而提出边界投影和轮廓投影的匹配算法。针对视图中存在的被打断的样条曲线,提出了分段样条曲线的爬坡算法来解决此类曲线不能匹配的问题。然后基于投影匹配序列重建出自由曲面的边界线,再由边界投影上的点和轮廓投影端点的对应关系重建出空间轮廓线。由轮廓线等参采样构造截面线并和边界线一起蒙皮生成最终自由曲面。本文提出的算法扩展了工程图的重建域。     

宽带声学多普勒流量剖面仪的系统仿真

90年代初发展起来的宽带声学多普勒流量剖面仪克服了传统窄带ADCP存在距离分辨力与速度分辨力之间的矛盾，从而解决了低速浅水河流流量(流速)精确测量的问题，是一种有着广泛应用前景的先进水文遥测仪器。文章中着重分析了BBADCP(宽带声学多普勒流量剖面仪)如何通过时间选通采样从河流不同深度返回的后向散射回波，实现测距离的目的；如何测量回波的多普勒频移，实现测流速的目的。文中从二维信号矢量的角度分析了多普勒频移调制和解调的过程，推导出提取速度信息的信号处理方法。文中最后采取等效基带仿真方法，运用匹配滤波器理论设计了一个BBADCP系统模型，通过仿真手段验证了文中对BBADCP的分析结果。     

浅谈基于矩阵运算的碎纸片拼接问题

随着科学技术的不断发展,碎片拼接技术在军事、医学、文物鉴定等各生活领域得到广泛的应用。碎片拼接复原其核心思想就是先将图像数字化,然后从图像边缘等概率提取子矩阵,根据计算机相应的程序对其进行拼接处理,最终实现全自动或是半自动的拼接复原。     

基于ICCP的地磁矢量匹配算法研究

针对基于等值线最近点迭代(ICCP)的地磁匹配算法在地磁总量特征相似区域应用时存在的误匹配问题,提出基于ICCP的地磁矢量匹配算法。该算法利用地磁矢量测量信息与匹配区域的矢量地磁图,采用三分量差异寻找地磁等值线附近的最优参考路径,进而求解刚性变换矩阵,通过刚性变换实现惯导指示路径的误差校正。仿真分析传统标量ICCP算法存在明显误匹配的情况及该情况下矢量匹配算法的校正效果,同时对比标量算法可以实现正确匹配情况下矢量算法的匹配效果。结果表明:基于ICCP的地磁矢量匹配算法不仅能够解决传统标量算法存在的误匹配问题,而且相对于标量算法具有更高的定位精度。     

组织中人岗匹配的测算模型及应用

将工作岗位标准的指标分为标准值型、区间值型和临界值型三类.针对前两种类型指标,应用空间距离和相关性的计算方法,给出了人与岗位的横向匹配与纵向匹配的测算模型;考虑到任职者的部分指标可能超过岗位标准,提出了截面匹配度的概念,并用任职者指标曲线的凸凹比例来刻画.最后通过计算实例验证了模型的有效性.     

高速列车车头纵剖面最大轮廓线辅助快速设计

目的研究符合设计师在Rhinoceros软件中三维草图建模习惯的计算机辅助高速列车车头纵剖面最大轮廓线设计方法。方法基于Rhinoceros二次开发高速列车车头纵剖面最大轮廓线辅助设计程序。分析曲线设计需求,根据NURBS曲线原理,将曲线控制点分为固定控制点、可左右水平移动控制点和可上下左右自由移动控制点三类,采用轮盘赌算法确定每个控制点的随机移动方向,根据产生的随机数和该控制点与相邻控制点距离最小值的乘积确认移动距离、移动控制点并生成若干NURBS曲线。结果在给定曲线基础上快速批量生成足够变异的NURBS曲线设计方案,供设计师选择,且曲线可持续迭代。结论相比此前对于基于NURBS建模的高速列车车头计算机辅助造型设计研究,在提高设计效率的同时,兼顾了设计师在Rhinoceros软件中的三维草图建模习惯。     

Three-dimensional angle measurement based on propagation vector analysis of digital holography

We propose what we believe to be a novel method for highly accurate three-dimensional (3D) angle measurement based on propagation vector analysis of digital holography. Three-dimensional rotations in space can be achieved by use of a CCD camera and a multifacet object, which reflects an incident wave into different directions. The propagation vectors of the reflected waves from the object can be extracted by analyzing the object spectrum of the recorded hologram. Any small rotation of the object will induce a change in the propagation vectors in space, which can then be used for 3D angle measurement. Experimental results are presented to verify the idea.     

Determination of three-dimensional displacement using two-dimensional digital image correlation

A novel method that uses a two-dimensional (2D) digital image correlation (DIC) based on a single CCD camera to measure three-dimensional (3D) displacement and deformation is proposed. Rigid-body displacement in 3D space consists of both in-plane and out-of-plane components. The presence of an in-plane displacement component results in a shift of the center of the image displacement vector, while the slope of the image displacement vector is related to the out-of-plane displacement component. Global DIC is employed to determine the displaced position of each point on an object based on a linear distribution characteristic of the displacement vector. Speckle images with deformation introduced by 3D displacement are generated to demonstrate the feasibility of the proposed method. In the 3D rigid-body displacement, both in-plane and out-of-plane displacement components are separated by determining the intercept and slope of the image displacement vector. In the 3D deformation, a zero order displacement (pure rigid-body displacement) mode is assumed in a small subset of pixels. Simulated and experimental results demonstrate that both in-plane and out-of-plane displacements can be accurately retrieved using the proposed method.     

Self-calibration of a binocular vision system based on a one-dimensional target

This paper proposes a method of self-calibration of a binocular vision system based on a one-dimensional (1D) target. This method only needs a 1D target with two feature points and the distance between the two points is unknown. During the process of computation, the distance value can be set an arbitrary value which is near the actual distance value. Using the method proposed in this paper, we can get the parameters of the binocular vision system including internal parameters of the two cameras and the external parameters (but there exists a non-zero scale factor in the translation vector which is connected to the initial distance value we set), the distortion parameters of cameras and the three-dimensional coordinates of the two points in different positions. In this paper, we determine theoretically that the initial distance value will not influence the results, and also the results of numerical simulation and experiment example are shown to demonstrate the method. Most importantly, this method is insensitive to the initial distance value, and it is the biggest advantage. In a practical application, we can use a 1D target with unknown distance to calibrate the binocular system conveniently; also we can use this method to calibrate the camera in a large field of view with a small 1D target.     

基于压缩量化与邻域空间LBP算子的图像哈希算法

目的为了解决哈希算法的感知鲁棒性与伪造检测能力不高的问题,提出基于特征压缩机制与邻域空间局部二值模式的紧凑图像哈希算法。方法首先利用2D线性插值技术,对输入图像进行预处理;嵌入Ring分割技术,将其变为二次图像;再利用Gabor滤波技术对其完成过滤;考虑到图像的颜色特征与其内在的空间关系,基于局部二值模式LBP设计邻域空间LBP算子,提取滤波图像的特征;构建特征压缩量化准则,输出紧凑的哈希二值数组;迭代Logistic映射,输出随机序列,通过量化每个序列值输出密钥流,通过构建动态引擎设计分段异加密模型,实现紧凑哈希序列的加密,获取图像哈希;最后计算原始哈希序列与待检测哈希序列的Hamming距离,实现图像信息的安全认证。结果与已有的哈希生成机制相比,文中算法所输出的哈希序列更紧凑,对旋转、伽马校正等篡改操作具有更好的感知鲁棒。结论所提哈希技术具备较高的安全性,在包装图标检索、信息检测等领域具有较好的价值。     

New Generation Model of Word Vector Representation Based on CBOW or Skip-Gram

Word vector representation is widely used in natural language processing tasks. Most word vectors are generated based on probability model, its bag-of-words features have two major weaknesses: they lose the ordering of the words and they also ignore semantics of the words. Recently, neural-network language models CBOW and Skip-Gram are developed as continuous-space language models for words representation in high dimensional real-valued vectors. These vector representations have recently demonstrated promising results in various NLP tasks because of their superiority in capturing syntactic and contextual regularities in language. In this paper, we propose a new strategy based on optimization in contiguous subset of documents and regression method in combination of vectors, two of new models CBOW-OR and SkipGram-OR for word vector learning are established. Experimental results show that for some words-pair, the cosine distance obtained by the CBOW-OR (or SkipGram-OR) model is generally larger and is more reasonable than CBOW (or Skip-Gram), the vector space for Skip-Gram and SkipGram-OR keep the same structure property in Euclidean distance, and the model SkipGram-OR keeps higher performance for retrieval the relative words-pair as a whole. Both CBOW-OR and SkipGram-OR model are inherent parallel models and can be expected to apply in large-scale information processing.     

Equivalent dose (palaeodose) estimation in thermoluminescence dating using a single aliquot of polymineral fine grains

A single aliquot protocol for the estimation of the natural dose in thermoluminescence dating (SATL) is presented that makes use of polymineral fine grains extracted from ceramic materials. The protocol is demonstrated using aliquots made from two Neolithic sherds and is compared with results from an additive dose polymineral technique. The results of both techniques are in close agreement and highlight the potential advantages of the new procedure, especially when sample availability is restricted, e.g. dating of small pottery fragments, or in cases of authenticity testing.     

基于曲率自适应的航空零件法矢量测量研究

现有的法矢量测量技术无法满足测量准确度和实时性的双重要求,法矢量计算方法不能适用于不同曲率的曲面。利用双目立体视觉,本文提出了一种基于曲率自适应的法矢量测量方法。首先,在双目立体视觉的基础上,基于变曲率曲面特征建立制孔区域曲面模型,提出投影点的布局方法;然后,基于三维重建的投影点数据,提出了基于曲面曲率自适应识别的法矢量计算方法;最后,针对小曲率曲面样件的测量结果,与三坐标测量仪测得的法矢量进行对比,用以验证本双目视觉测量方法的精度。实验结果表明:该方法测量法矢量误差为1.6°。该方法可有效提高法矢量测量的准确度,满足大型航空零件现场测量的工程要求。     

Multi-objective sequence optimization of PCB component assembly with GA based on the discrete Fréchet distance

A new mechanism,namely a combination of curve matching method based on the discrete Fréchet distance and evolutionary algorithms,is proposed to solve pick-and-place sequence optimisation problems as a multi-objective optimisation problem. The essence of the mechanism is to accomplish the comparison of objective vectors with curve matching method. The objective vector is mapped into the array of points with a binary mapping operator and the discrete Fréchet distance is utilised to measure the similarity between the reference array of points and the comparison array of points. The genetic algorithm based on the discrete Fréchet distance (FGA) is proposed. To test the new mechanism, together with FGA, three other test algorithms are selected to solve the sequence optimisation problem. The simulation results indicate that FGA outperforms other algorithms. This new mechanism is rational and feasible for multi-objective pick-and-place sequence optimisation problems.     

Three-dimensional object detection under arbitrary lighting conditions

A novel method of 3D object recognition independent of lighting conditions is presented. The recognition model is based on a vector space representation using an orthonormal basis generated by the Lambertian reflectance functions obtained with distant light sources. Changing the lighting conditions corresponds to multiplying the elementary images by a constant factor and because of that, all possible lighting views will be elements that belong to that vector space. The recognition method proposed is based on the calculation of the angle between the vector associated with a certain illuminated 3D object and that subspace. We define the angle in terms of linear correlations to get shift and illumination-invariant detection.     

三维无旋矢量场的一种新的可视化方法

提出了三维无旋矢量场的一种新的可视化方法,即构造空间曲面,使得矢量场在曲面上任意一点处垂直于该曲面。首先找到曲面所满足的偏微分方程组,通过采用类似于经典四阶龙格―库塔方法的数值解法对其求解,得到曲面上的离散点,然后进行三角剖分,从而得到逼近于曲面的空间三角网格。论文的偏微分方程组的求解借鉴了常微分方程求解算法的设计思想,构造出的曲面与传统的点图标和线图标相比,在更大程度上揭示了矢量场本身的连续性。