摄像机径向畸变校正和内参估计的单图标定方法

提出了一种对摄像机的径向畸变进行校正和内参数估计的单图标定方法.拍摄一幅平面标定模板图像,提出若干条直线,拟合在单参数除法畸变模型下的圆弧参数,从而估计出径向畸变.对径向畸变进行校正后,利用标定模板点与经过校正后的图像点之间的对应关系,估计出单应性矩阵.在假定摄像机主点与畸变中心重合的条件下,线性地计算出摄像机焦距初值.以上述线性方法得到的结果为初值,进行非线性优化,最终得到准确的摄像机参数.超广角鱼眼相机和普通数码相机的实验结果表明,本文提出的算法实现简单、适用性广,结果准确,具有较强的实用性.     

基于两步法的摄像机标定算法

摄像机标定是机器视觉中的一个重要问题.精确的摄像机标定在涉及定量测量的应用中是非常重要的.摄像机标定的目的是得到摄像机的内部参数和外部参数.通过这些参数我们能够将一个点的三维位置与它的图像平面的坐标相匹配.本文提出了一种基于两步法的摄像机标定方法.第一步,使用基于无畸变的相机模型估计标定参数;第二步,在考虑相机畸变的情况下,对第一步中得到的标定参数通过非线性优化进行迭代优化,并求解畸变系数,包括径向畸变系数和切向畸变系数.用单幅图像即可完成标定,标定过程比两步法更为简洁.实验结果表明,这种算法是简单而有效的.     

基于网格靶标快速高精度摄像机标定方法

本文针对单摄像机成像特点,首先建立其实际成像数学模型,为快速高精度的标定摄像机参数,靶标采用平行网格线靶标,有效利用直线的平行性约束条件,可高效的求取目标点,此种方法先求解摄像机纵横比,然后利用参数分离的方法通过迭代求解其余模型参数,从而简化了求解过程,将标定结果与Tsai法相比较可知,标定精度相当。     

基于交比不变性的投影仪镜头畸变参数标定方法

利用了透视投影中的交比不变的性质,针对由CCD和投影仪组成的测量系统,在CCD已经标定的情况下,仅考虑投影仪畸变模型为一阶径向畸变的情况,只需要投影仪投射共线的投影坐标已知的4个点,利用交比不变性,建立一元二次方程就可以标定投影仪镜头的畸变参数.该方法的特点是算法简单,易于实施,需要已知条件较少.     

基于交比不变性的分区域相机畸变矫正

针对相机不同畸变程度的大视场区域很难同步等精度标定的问题,提出基于交比不变性的分区域相机畸变矫正方法。以相机主点为中心,按距离加权原则将相机视场区域分割为若干个区域;利用各分割视场区域中的多组共线4点坐标建立交比不变性畸变系数求解模型;据此实现分区域相机畸变矫正。此方法的测量误差的评价是通过比较直线偏移量来实现的。实验表明,两区域分割法和三区域分割法的直线偏移量误差比传统不分区方法分别降低14.7%和29.93%。此方法在传统方法的基础上进行改进,解决大视场区域非等精度标定。从实验结果可得到此方法优于传统方法。     

基于共面点的摄像机线性标定法

提出了一种线性求解摄像机内外参数的方法。通过分解参数确定相机主点坐标和纵横比,利用径向平行约束求解大部分的外参数,再引入新的畸变模型线性求解其余内外参数。该法特点是采用共面点标定物,且不需摄像机做任何运动就可以实现全过程的线性标定。既避免了非线性优化的繁琐和不稳定,也解决了其它线性法中部分内参数的标定问题。两套实验结果误差分别为0.3391pixels和0.6004pixels,表明该法具有较高的精度,是一种简单、有效、实用的标定法。     

广角镜头桶形畸变的样条函数修正方法

为了修正广角镜头的桶形畸变,本文提出了一种基于样条函数的修正方法.依据镜头桶形畸变产生的物理机制,本文首先制作了一个同心圆标定模板并用该模板对广角镜头进行标定.然后利用样条函数的光滑性和桶形畸变的径向连续性,采用三次样条函数拟合桶形畸变规律.最后,用该样条函数拟合的桶形畸变规律对同一个视觉系统拍摄的变形图像进行恢复.在实验中,该方法能够对畸变图像进行快速恢复并表现出良好的效果.因此对于固定焦距视觉系统,在不考虑视觉系统具体参数的情况下,新的方法能够快速有效地对广角镜头桶形畸变进行修正.     

一种摄像机自标定的线性方法

提出了一种基于空间共面直线从单幅图像进行摄像机自标定的线性方法.本方法结合工程应用实际,直接利用场景的直角信息,根据点的中心投影关系,推导直线的投影关系,基于平面上不平行的3条直线,由单幅图像线性的高精度的标定出摄像机内、外参数.算法用仿真实验和实拍图像都得到了精确、可靠的结果,在精度上明显优于基于共面点的算法.     

大视场线结构光视觉传感器的现场标定

针对大视场线结构光视觉传感器的现场标定,提出了一种基于自由组合一维靶标的标定方法。自由组合多个一维靶标并固定,其中每个一维靶标至少包含3个共线特征点。靶标在传感器测量空间内自由摆放至少两次。以一维靶标两两之间夹角恒定为约束求解摄像机内部参数;由一维靶标消影点性质和特征点之间距离约束,求解各特征点在摄像机坐标系下的空间坐标;根据交比不变计算光平面与各一维靶标交点的摄像机坐标,拟合出光平面方程。实验表明,该方法可获得与平面靶标相当的标定精度,具有靶标加工容易、精度高、摆放次数少的特点,适合大视场线结构光视觉传感器的现场标定。     

船用光电系统中摄像机参数的标定方法

基于一阶径向畸变的针孔摄像机模型,提出了一种新的线性三步摄像机定标方法,即通过径向排列约束计算摄像机参数的旋转矩阵、X轴平移矢量和Y轴平移矢量;根据透视投影的交比不变性解算一阶径向畸变参数;利用求得的摄像机参数建立有效焦距和Z轴平移矢量的线性方程,采用最小二乘法得到线性解。实验表明,该方法简单快捷,具有较高的标定精度,解决了原有算法采用非线性搜索寻优可能存在的解不稳定性等问题。     

X射线光刻掩模加工过程中的形变研究

对以SiNx为衬基的X射线光刻掩模在背面刻蚀过程中的形变进行数值仿真,研究了Si片和衬基的各种参数对掩模最大平面内形变和非平面形变的影响.结果表明,参数的变化明显影响最大非平面形变量.当Si片的厚度和直径增大,衬基的厚度和初始应力减小时,最大平面内形变与非平面形变减小,而衬基的材料对两者的影响不明显.     

三维重构视觉系统的标定

文章基于改进两步法的标定思想,在三维重构中提出了一种新的视觉系统参数标定与镜头畸变修正方法.该方法根据图像中心附近点畸变量较小的性质,利用中心附近点和全场视点对CCD相机和DLP投影仪的内外部参数标定和镜头畸变修正进行分离.在标定过程中,所设计的带标准圆阵列的靶标和伪随机连续方形编码可以实现特征点的自动识别和匹配.实验表明,该方法能快速、方便地对视觉系统参数进行标定和镜头畸变修正.     

A 20‐node hexahedron element with enhanced distortion tolerance

This paper presents a distortion resistant 20‐node hexahedron element that employs two different sets of shape functions for the trial and test functions. The formulation seeks to satisfy the continuity and completeness requirements by exploiting the intrinsic properties of these two sets of shape functions. Several test problems are used to assess the performance of the element under various mesh distortions. The ability of the proposed as well as the classical 20‐node element to maintain solution accuracy under severe mesh distortions has been studied. The proposed element exhibits a very high tolerance to mesh distortions. In particular, for problems involving linear and quadratic displacement fields, the element is capable of reproducing exact solution under all admissible geometrical distortions of the mesh. For test problems involving higher‐order displacement fields, the performance of the present element is in general better than that of the classical element. Copyright © 2004 John Wiley & Sons, Ltd.     

正弦波形畸变和失真度的分析

测试波形的畸变程度可用波形的失真度来表示.目前常用的频域法求取和计算失真度的结果与波形的畸变有背离的地方.实际失真度很大,测出来的值却偏小.本文提出一种INV时频法,可以弥补频域法的缺陷,文内给出了计算实例.     

Controlling of Distortion by means of Quenching in adapted Jet Fields

Controlled temporal and/or spatial inhomogeneous (adapted) quenching within the heat treatment process creates the possibility of influencing the distortion of a workpiece. Suitable heat transfer conditions at the workpiece surfaces within the quenching process are realized by impressing and regulating of adjusted flexible flow fields on the basis of jet arrays inside liquid or gaseous media. For analysis of workpiece distortion in heat treatment, the locally asymmetric quenching process is analysed and modelwise described in the framework of the Collaborative Research Centre (SFB570) “Distortion Engineering” at the University of Bremen. Here the potential of measures for avoidance as well as reduction of distortion within the heat treatment process is appraised on the basis of simulation models. These model calculations are verified by experimental examinations on the asymmetric quenching of simple shaped parts like rings of SAE 52100 (100Cr6) and cylinders of AISI 5120 (20MnCr5) in the framework of flexible quenching conditions.     

Quadratic serendipity finite elements over convex polyhedra

The conventional approach to construct quadratic elements for an n‐sided polygon will yield n(n+1)/2 shape functions, which increases the computational effort. It is well known that the serendipity elements based on isoparametric formulation suffers from mesh distortion. Floater and Lai proposed a systematic way to construct higher‐order approximations over arbitrary polygons using the generalized barycentric and triangular coordinates. This approach ensures 2n shape functions with nodes only on the boundary of the polygon. In this paper, we extend the polygonal splines approach to 3 dimensions and construct serendipity shape functions over hexahedra and convex polyhedra. This is done by expressing the shape functions using the barycentric coordinates and the local tetrahedral coordinates. The quadratic shape functions possess Kronecker delta property and satisfy constant, linear, and quadratic precision. The accuracy and the convergence properties of the quadratic serendipity shape elements are demonstrated with a series of standard patch tests. The numerical results show that the quadratic serendipity elements pass the patch test, yield optimal convergence rate, and can tolerate extreme mesh distortion.     

A Review of HTS Thick-Film Microwave Filter Technology

For 10 years, thick-film YBCO has been used to make radio frequency filters out of three-dimensional superconductor coated structures. These filters are presented in a detail never before revealed. The chronology of solving technical problems such as coating and construction will be recounted from a historical perspective. The most recent design, which results in a 16-pole, 1.9 GHz filter in a housing measuring 145 mm×60 mm×35 mm, will be shown in detail. We will discuss the challenges in resonator design, substrate fabrication, coating technology, filter design, and filter realization associated with this filter. This overview demonstrates the progression of size over the past decade, resulting in an order of magnitude reduction in filter size and lessening size as a concern for system application of thick-film HTS filters. The impact of this size reduction on performance metrics such as Q and realizable filter order, as well as device characteristics such as intermodulation distortion, will be shown.     

Thermal and mechanical evolution of welding‐induced buckling distortion

Abstract

The evolution of the buckling phenomenon starts during the weld cooling cycle, caused by an onset inelastic strain incompatibility condition. This initial bifurcation phenomenon may continue to grow until the completion of the cooling cycle, which results in the final buckling distortion of the plate. With lower heat input and/or smaller plate dimensions this initial instability may stop during the cooling cycle due to diminishing strain incompatibility and recovering of the plate rigidity. The buckling evolution process is complex due to the highly nonlinear nature of the welding problem. This paper studies this buckling evolution process using an integrated experimental and numerical approach. Bead‐on‐plate welds of AH36 steel were experimentally studied. The welding process was numerically simulated and analyzed using a three‐dimensional, thermo‐elastic‐plastic, large deformation model. The transient stress bifurcation phenomenon and the displacement evolution process were analyzed to understand the critical weld conditions causing the final buckling distortion of the weldment. The critical weld conditions were evaluated on the longitudinal inherent shrinkage (plastic) strain distribution in the weldment.     

Control of Titanium Alloy Thin Plate Welding Distortion by Trailing Peening

The technology of trailing peening is a kind of promisingly bran-new technology which can be used to control weldingstress and distortion of Ti alloy thin plate. Control of TC4 Ti alloy thn plate welding stress and distortion underthe condition of convent     

略阳电厂84.8m双曲线冷却塔定向爆破拆除

针对略阳电厂双曲线冷却塔高、大、壁薄的结构特点以及爆破周围环境安全要求,通过选定合适的切口形式、切口大小、切口角度以及选择合理的爆破孔网参数,对冷却塔实施了定向爆破.冷却塔起爆后在空中经过短暂的扭曲变形,最后按预计方向倒塌在安全范围内,破碎效果良好,爆堆高度只有4-5 m,达到了预期的爆破效果.爆破实践表明,高大、薄壁双曲线型冷却塔在定向爆破过程中要发生扭曲变形,扭曲是否顺利,直接影响到冷却塔的倒塌方向和破碎效果,值得在类似工程爆破中引起注意.