条纹投影动态三维表面成像技术综述

对条纹投影动态三维表面成像技术进行了总结,分析了典型方案的特点。首先介绍了该技术的基本原理,包括系统基本结构、三维表面成像原理及相移法和傅立叶变换法这两种典型的相位提取方法。接着介绍了动态成像方案,包括高速投影方案和采用速度相对低的相机进行动态三维表面成像的方案。然后介绍了动态三维成像中绝对相位获取方法,主要是模拟和数字编码法及区域统计特性编码法。最后介绍了高精度动态相位测量方案。     

相位测量轮廓术中投影条纹畸变的研究

在传统的采用发散照明的相位测量轮廓术中,为了准确得到被测物体的高度分布,测量前必须将参考平面坐标与相位分布之间的映射关系计算出来并以数据表的形式存储在计算机中备用。文中研究改进了投影条纹的分布,使投影到参考面上的条纹满足周期性分布,参考面上的相位分布是坐标的线性函数,无须提前将参考面坐标与相位分布的映射关系计算好并储存于计算机中,提高了测量精度,简化了实验装置。实验表明所提出方法的可行性与有效性。     

相位拼接闭合条纹干涉图处理技术

二维傅里叶变换法处理闭合条纹干涉图时,解调的相位含有符号突变.为矫正符号偏差,提出一种算法,通过一对正交的半侧低通滤波器得到4个含有符号突变的相位面,将其中符号正确的部分进行拼接以得到正确的相位分布.该方法计算量小,并且能有效避开符号突变位置的相位失真区域;选择了合适的滤波窗,并对干涉条纹圆心附近区域的相位进行单独低通...     

条纹投影与相位偏折测量技术研究进展

条纹投影和相位偏折测量术可用于精确地测量待测物面形,在全场光学三维轮廓测量领域具有较好的发展前景。首先,介绍了条纹投影和相位偏折测量技术的基本原理,重点是这两种技术中的相位提取技术、摄像机定标技术等关键技术。其次,对条纹投影和相位偏折测量术这两种测量方法的异同点做了对比。最后,介绍了条纹投影和相位偏折测量技术在提升测量精度和速度方面的发展。为了提升测量精度,主要有校正条纹Gamma效应、提升相位提取精度、摄像机标定精度和相位-高度/梯度标定精度等途径;为了提升测量速度,主要有提升相位提取速度、相位解包裹速度等方法。     

条纹投影测量系统的相位误差抑制方法

针对投影仪和相机的伽马非线性效应会使解包裹相位结果产生周期性误差的问题,提出一种基于均值模板的相位误差抑制方法.首先对解包裹相位进行傅里叶变换,计算出相位误差的周期值.之后,设计出长度可变的一维均值滤波模板,模板的长度与相位误差的周期相关.最终用此模板对解包裹相位进行均值滤波,消除周期性误差.实验结果显示,所提方法使解...     

基于条纹跟踪的动态过程三维轮廓术

针对在快变化动态过程三维轮廓术中,成像设备拍摄频率不满足抽样定理,对物体表面动态条纹时间采样不足以及物体表面发生破裂的动态过程,提出一种采用标记条纹进行跟踪的动态过程三维轮廓术,能有效地解决因成像设备时间采样不足和条纹断裂对三维相位展开所带来的影响问题,获得物体正确的动态面形分布,计算机模拟证实了此种方法的正确性。     

颜色编码正弦条纹实现孤立动态物体3维测量

采用常规条纹投影与相位分析方法,对动态物体,尤其是空间存在孤立区域、分布不连续的动态物体进行3维面形测量时,很难得到可靠的展开相位。为了解决这一问题,提出一种用颜色编码正弦条纹光栅投影测量的新方法。该方法使用二级编码的颜色信息来标记待投影的正弦条纹,从另一角度拍摄记录带有颜色信息的变形条纹图,根据编码特征进行解码获取颜色级次来确定条纹级次,并指导截断相位的展开,重建空间孤立动态物体的3维面形数据。结果表明,该算法的编码稳定、解码方式可靠,只需要拍摄1幅图就可以较好地重建空间孤立物体的3维面形。     

基于光流场理论测量物体变形相位的新方法

基于光流场理论,提出一种由两幅条纹图像解调出 物体变形相位的新方法。首先根据光流场理论,获 得两帧连续图像之间的光流矢量场;然后运用双幅图像中初始图像的条纹频率与矢量场进行 计算,获得 物体的全场变形相位分布。模拟结果和实 验结果表明,本文算法将直观的运动矢量场和变形相位的提取相联系,能够解调出物体变形 相位信息, 不需要相位解包络运算,过程简单方便,并且在条纹越密集处提取的变形相位信息越准确。 本文方法为计算 物体全场变形相位分布和动态测量提供了新的途径。     

2维载频条纹傅里叶变换轮廓术

为了在3维形貌测量中解决非连续物体所存在的非连续相位解包问题并提高测量精度,提出采用2维网格光栅作为空间载频条纹的傅里叶变换轮廓术。首先应用2维傅里叶变换对2维光栅条纹图像进行频谱分析;然后设计带通滤波器分离出两个1维变形光栅条纹,在1幅变形网格光栅条纹得到两个1维光栅各自所对应的包裹相位分布;最后应用查表法进行解包得到确定的调制相位分布,给出了详细的理论推导和实验结果。结果表明,采用2维网格光栅+查表相位解包法很好地解决了1维单一频率光栅条纹的低测量精度、1维双频光栅的频率混叠以及3维测量中高度不连续所存在相位解包问题,该方法是可行的。     

基于图像拼接和双频投影栅线法的三维形貌测量

为解决采用光栅投影式三维轮廓术测量物体三维形貌时,出现的条纹图样的不连续性,利用计算机编程,生成由两种不同频率合成的复合光栅,将它投影到被测物体上,并将被测物体放在精密的旋转平台上,通过二次成像后对两幅图像进行图像拼接,得到清晰的被光栅调制的物体图像,再对图像进行傅里叶变换,然后采用滤波器滤出相应的高频和低频成分,利用低频光栅的相位差辅助解出高频光栅的真实相位差,从而实现物体的三维形貌重建.结果表明,本方法简单、精度高,可以成功解决有突变面形和投影时具有阴影的物体的三维形貌测量问题.     

位相法三维形貌测量数值模拟系统

设计了位相法三维形貌测量数值模拟系统.实验结果表明,该系统可以模拟相位测量的主要过程,根据模拟物体和系统参数对投影光栅进行有效调制,并利用行列法对调制光栅得到的包裹相位图正确解包裹.本系统为研究各种高效健壮的相位解包裹算法提供了模拟平台.     

High precision traffic measurement

Making passive measurements is a challenging process. A small number of research groups have overcome these difficulties and have made terabytes of captured network traffic available to the Internet community. We have discovered that even when initial hurdles to collecting traces have been overcome, there are potentially many methodological weaknesses that can severely limit the usefulness of the data collected. This article describes these weaknesses and suggests methodologies to avoid them. Five case studies from the work of the University of Waikato's WAND network research group are presented. These studies illustrate the need for care at all stages of the measurement process, analysis, and presenting the results     

高精度GPS动态测量分析

GPS定位技术凭借其高精度以及全天候的特点,被广泛的应用在地测量学、地球动力学、地球物理学、天体力学、载人航天学、全球海洋学和全球气象学等领域中。本文主要论述了高精度GPS动态测量技术的工作原理,GPS动态测量技术的发展现状,动态测量技术的优点和缺点,对动态测量结果的精度进行了论述,并且介绍了GPS动态测量技术的应用。     

基于FTP的动态相位展开方法的研究

在采用结构照明的光学三维传感方法中 ,相位展开是被测物体三维面形正确重建的关键步骤之一 ,也是一个难点。本文就动态傅里叶变换轮廓术中相位展开问题进行研究 ,对比分析了直接相位展开算法、基于相邻帧间相位差之间的相位展开算法和基于调制度排序的相位展开算法。解决了基于傅立叶变换轮廓术的动态三维测量中相位展开问题 ,特别是孤立区域的相位展开。为动态傅立叶变换轮廓术的在冲击和爆轰过程中应用 ,提供了理论基础。文中给出了详细的理论分析和计算机模拟     

Full-field 3-D measurement of solder pastes using LCD-based phase shifting techniques

Quality inspection of deposited solder pastes is critical in surface mounting processes. As surface-mount technology (SMT) component pitches decrease, three-dimensional (3-D) measurement of solder pastes has become more and more important in ensuring solder joint reliability. Currently, the 3-D measurements for solder pastes are mainly performed by laser-based systems. However, they suffer from low inspection speed due to the physical line-scanning process. In this paper, a fast and cost-effective 3-D measurement system for deposited solder pastes is proposed. The proposed system uses a liquid crystal display (LCD)-based phase shifting technique to perform full-field 3-D measurement of solder pastes with high accuracy. Experiments have shown that the 3-D profiling and volume measurement of solder pastes are very efficient and effective with the proposed system. The volume measurement repeatability is in the micrometer range. The processing time of the proposed 3-D measurement system for an image of 640/spl times/480 pixels is less than 1 s on a typical personal computer.     

提高DSSS信号PN码相位测量精度的三点二次插值法

提出了利用三点二次插值法处理相关谱谱峰数据以提高DSSS(直序扩频)信号PN码相位测量精度的算法。该算法利用相关谱谱峰及其邻近的2个数据点确定二次插值多项式,然后求取插值多项式的极大值点以确定相关谱谱峰精确位置,有效地提高DSSS信号PN码相位的测量精度。实验结果表明,该算法实现了大幅度提高PN码相位测量精度的目的。     

2-D phase unwrapping and instantaneous frequency estimation

The phase of complex signals is wrapped since it can only be measured modulo-2π; unwrapping searches for the 2π-combinations that minimize the discontinuity of the unwrapped phase, as only the unwrapped phase can be analyzed and interpreted by further processing. Given an estimate of the phase gradient (i.e., of the instantaneous frequency), the 2-D unwrapped phase can be obtained as a solution of a variational problem. The analysis of unwrapping is done quite separately from instantaneous frequency estimation so that the reliability of both steps can be assessed independently. Various methods for evaluating 2-D instantaneous frequency are presented and compared in the presence of noise and amplitude variations. A study has also been made on aliasing arising in areas where, with respect to instantaneous frequency, spatial sampling is insufficient. The presence of noise in the data further complicates phase aliasing analysis since there is no way to distinguish between the aliasing due to noise or that due to steep phase slopes     

A correction method of color projection fringes in 3D contour measurement

In the three-dimensional (3D) contour measurement, the phase shift profilometry (PSP) method is the most widely used one. However, the measurement speed of PSP is very low because of the multiple projections. In order to improve the measurement speed, color grating stripes are used for measurement in this paper. During the measurement, only one color sinusoidal fringe is projected on the measured object. Therefore, the measurement speed is greatly improved. Since there is coupling or interference phenomenon between the adjacent color grating stripes, a color correction method is used to improve the measurement results. A method for correcting nonlinear error of measurement system is proposed in this paper, and the sinusoidal property of acquired image after correction is better than that before correction. Experimental results show that with these correction methods, the measurement errors can be reduced. Therefore, it can support a good foundation for the high-precision 3D reconstruction.