New Approach for 3D Shape Measurement Based on Color-Coded Fringe and Neural Network

A new 3D surface contouring and ranging system based on digital fringe projection and phase shifting technique is presented. Using the phase-shift technique, points cloud with high spatial resolution and limited accuracy can be generated. Stereo-pair images obtained from two cameras can be used to compute 3D world coordinates of a point using traditional active triangulation approach, yet the camera calibration is crucial. Neural network is a well-known approach to approximate a nonlinear system without an explicit physical model, in this work it is used to train the stereo vision application system to calculating 3D world coordinates such that the camera calibration can be bypassed. The training set for neural network consists of a variety of stereo-pair images and the corresponding 3D world coordinates. The picture elements correspondence problem is solved by using projected color-coded fringes with different orientations. Color imbalance is completely eliminated by the new color-coded method. Once the high accuracy correspondence of 2D images with 3D points is acquired, high precision 3D points cloud can be recognized by the well trained net. The obvious advantage of this approach is that high spatial resolution can be obtained by the phase-shifting technique and high accuracy 3D object point coordinates are achieved by the well trained net which is independent of the camera model works for any type of camera. Some experiments verified the performance of the method.

Multi-objective strategy to optimize dithering technique for high-quality three-dimensional shape measurement

Dithering optimization techniques can be divided into the phase-optimized technique and the intensity-optimized technique. The problem with the former is the poor sensitivity to various defocusing amounts, and the problem with the latter is that it cannot enhance phase quality directly nor efficiently. In this paper, we present a multi-objective optimization framework for three-dimensional(3D) measurement by utilizing binary defocusing technique. Moreover, a binary patch optimization technique is used to solve the time-consuming issue of genetic algorithm. It is demonstrated that the presented technique consistently obtains significant phase performance improvement under various defocusing amounts.

PCA-based 3D Shape Reconstruction of Human Foot Using Multiple Viewpoint Cameras

This paper describes a multiple camera-based method to reconstruct the 3D shape of a human foot. From a foot database, an initial 3D model of the foot represented by a cloud of points is built. The shape parameters, which can characterize more than 92% of a foot, are defined by using the principal component analysis method. Then, using ＂active shape models＂, the initial 3D model is adapted to the real foot captured in multiple images by applying some constraints （edge points＇ distance and color variance）. We insist here on the experiment part where we demonstrate the efficiency of the proposed method on a plastic foot model, and also on real human feet with various shapes. We propose and compare different ways of texturing the foot which is needed for reconstruction. We present an experiment performed on the plastic foot model and on human feet and propose two different ways to improve the final 3D shapers accuracy according to the previous experiments＇ results. The first improvement proposed is the densification of the cloud of points used to represent the initial model and the foot database. The second improvement concerns the projected patterns used to texture the foot. We conclude by showing the obtained results for a human foot with the average computed shape error being only 1.06 mm.

Auto-measuring System of 3-Dimensional Human Body

To realize the automation of fashion industry measuring,designing and manufacturing, the auto-measurement of 3D size of human body is of great importance. The auto measurement system of 3D human body based on Charge Coupled Devices (CCD) and infrared sensors is presented in this paper. The system can measure the bare size of human body that excludes the effect of clothing quickly and accurately.

Optimized dithering technique in frequency domain for high-quality three-dimensional depth data acquisition

On the basis of the objective functions,dithering optimization techniques can be divided into the intensity-based optimization technique and the phase-based optimization technique.However,both types of techniques are spatial-domain optimization techniques,while their measurement performances are essentially determined by the harmonic components in the frequency domain.In this paper,a novel genetic optimization technique in the frequency domain is proposed for highquality fringe generation.In addition,to handle the time-consuming difficulty of genetic algorithm(GA),we first optimize a binary patch,then join the optimal binary patches together according to periodicity and symmetry so as to generate a full-size pattern.It is verified that the proposed technique can significantly enhance the measured performance and ensure the robustness to various amounts of defocusing.

Tides and short-term variabilities in the Kuroshio west of Yonakuni-jima

Direct current measurements at the mooring station M southwest of Yonakuni-jima are carried out from May 18 to June 1, 1996. The Observed Kuroshio Current at 290 and 594 m depths of the mooring station M is quite steady ddring the pened of Observation. The rotary spectral estimates of the current data by the maximum entropy method show that there are prominent diurnal and semidiurnal spectral peaks. The semidiurnal tide is predominant at 290 m depth while there is the current fluctuation with the inertial period except for the tidal oscillation at 594 m depth. There are also peaks at the pened of 4-7 d. There is a significant coherence between two time series of currents at 290 and 594 m depths in the pened range of 3 - 5 d. The Japan Meteorological Agency (JMA) wind data during the same period as the oceanic measurement are used in comparison with the current meter data. Rotary spectral estimates for the wind data show significant peaks at the period of 3 - 5 d. It is concluded from the cross spectra between the wind and the current that the current fluctuation of 3 - 5 d period at 290 m depth response to the wind fluctuation of the same periods with time lags smaller than 1 d.

Investigation on 3Dt wake flow structures of swimming bionic fish

A bionic experimental platform was designed for the purpose of investigating time accurate three-dimensional flow field, using digital particle image velocimetry （DSPIV）. The wake behind the flapping trail of a robotic fish model was studied at high spatial resolution. The study was performed in a water channel. A robot fish model was designed and built. The model was fixed onto a rigid support frame- work using a cable-supporting method, with twelve stretched wires. The entire tail of the model can perform prescribed motions in two degrees of freedom, mainly in carangiform mode, by driving its afterbody and lunate caudal fin respectively. The DSPIV system was set up to operate in a trans- lational manner, measuring velocity field in a series of parallel slices. Phase locked measurements were repeated for a number of runs, allowing reconstruction of phase average flow field. Vortex structures with phase history of the wake were obtained. The study reveals some new and complex three-dimensional flow structures in the wake of the fish, including ＂reverse hairpin vortex＂ and ＂reverse Karman S-H vortex rings＂, allowing insight into physics of this complex flow.

3-D Shape Measurement of Complex Objects by Combining Color-Coded Fringe and Neural Networks

A new approach for three dimensional (3-D) shape measurement was proposed based on colorcoded fringe and neural networks. By applying the phase-shift technique to fringe projection, point clouds were generated with high spatial resolution and limited accuracy. The picture element correspondence problem was solved by using projected color-coded fringes with different orientations. Once the high accurate corresponding points were decided, high precision dense 3-D points cloud was calculated by the well trained net. High spatial resolution can be obtained by the phase-shift technique and high accuracy 3-D object point coordinates are achieved by the well trained net, which is not dependent on the camera model and will work for any type of camera. Some experiments verify the performance of this method.

A Novel 360°3D Profilometry

A new method of 360° turning 3D shape measurement in which light sectioning and phase shifting techniques are both used is presented in this paper.A sine light field is applied in the projected light stripe,meanwhile phase shifting technique is used to calculate phase of the light slit.Thereafter wrapped phase distribution of the slit is formed and the unwrapping process will be made by means of the height information based on the light sectioning method.Therefore phase measuring results with better precision can be obtained.At last the target 3D shape data can be produced according to geometric relationships between phases and the object heights.The principles of this method are discussed in detail and experimental results are shown in this paper.

Dual-frequency fringe for improving measurement accuracy of three-dimensional shape measurement

A new phase unwrapping method based on dual-frequency fringe is proposed to improve both high accuracy and large measurement range of three-dimensional shape measurement by synthesizing the projected dual-frequency fringes obtaining higher and lower frequencies.The lower-frequency one is their phase difference,which can help unwrap the wrapped phase of the higher-frequency one from their phase sum.In addition,the relationship between the measuring accuracy and the frequencies of the projected fringes is studied to guide the frequency selection in actual measurement.It is found that the closer the two frequencies are,the higher the measurement accuracy will be.The computer simulation and experiment results show the viability of this method.

基于LCD数字投影技术的傅里叶变换法测量物体三维形貌

利用数字投影栅线技术,采集变形前后的两幅图像,存入计算机中,然后根据Fourier变换原理进行处理,解调出物体的形貌信息.整个过程自动化程度较高,尤其是投影栅线为正弦栅线且栅距随意可调,比栅板投影栅线所含噪音小,因此精确度较高,而且使用的仪器常见,对环境要求低,简便易行,有利于进一步推广.给出对爆竹像的实际测量结果,结果表明了该方法的实用价值.

基于傅里叶变换去隔行图像的动态3维面形测量

为了解决动态面形测量中隔行扫描CCD相机记录动态物体表面变形条纹图像存在缺陷的问题,提出了傅里叶变换去隔行算法,即把隔行扫描CCD获取动态物体的错位模糊帧图像分成两个单场图像,分别对每一单场图像进行傅里叶变换去隔行处理,再利用条纹分析法重建对应时刻的3维面形。理论分析得出单场傅里叶变换去隔行图像与对应的准确满帧图像相同的结论。结果表明,该方法可以很好地恢复条纹和重建物体,且简单实用,可用于基于空间相位检测、相位测量轮廓术、傅里叶变换轮廓术等条纹分析方法的动态物体3维测量中。

基于小物体的LCD数字相移条纹投影轮廓测量

采用数字相移条纹投影技术,利用计算机生成具有高对比度和较高亮度、并有一定相差的正弦条纹,用数字投影仪将这些条纹图依次投射到被测物体表面,相位移动由软件控制,这一过程即实现了数字相移投影,避免了传统相移带来的各种误差.可以根据不同尺寸的面形确定最优的投影条纹,使得系统适应性强,操作简单,并能得到较高的测量精度.实验证实可实现小物体面形自适应测量.

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。

一种管道内3维形貌检测系统

为了解决常见结构光管道内3维形貌检测系统存在光线遮挡引起测量误差和"盲区"的问题,采用了一种新改进的圆结构光垂直照明、用两个互补金属氧化物半导体摄像机同步拍摄的管道内3维形貌检测系统,建立了适合该系统的图像处理和系统标定方法,完成了检测实验。结果表明,该系统可以很好地解决"盲区"问题,减小了测量误差,系统的标准差为0.50mm,并能得到完整的管道内壁3维形貌信息。

条纹投影动态3维测量中相位高精度估计

为了提高条纹投影动态3-D形貌测量精度,采用加窗傅里叶分析辅助相移的方法来减小运动导致的相移误差。首先采用加窗傅里叶分析法估计变形条纹间的实际相移量,然后采用最小二乘法估计出变形条纹的高精度相位分布,最后由估计的相位计算得到场景3维形貌。理论分析了物体运动对相移量的影响,通过仿真研究了所提方法的相移量估计精度,并搭建了实验系统进行验证。结果表明,实验中采用所提方法的相位恢复精度达到0.1673rad,比现有方法有明显提高。该方法用来提高条纹投影动态3-D形貌测量中相位精度是有效的。

Influence of Different Lubricants on Deformation Behaviour of IN 718 Alloy in Hot Compression Process

The influence of different lubricants on the deformation behaviour of IN 718 alloy was studied. The results show that, with the improvement of lubrication condition, the deformation of the alloy tends to be homogeneous, and the resistance of deformation decreases. Consequently, FR 2 glass lubricant is considered to be an ideal choice when the relationship between stress and strain of IN 718 alloy is measured by means of hot compression experiment.

基于条纹反射的镜面测量及三维重建算法分析

本文详细介绍了依据条纹反射术测量镜面、类镜面的原理和方法,分析了经由梯度数据重建三维面形的主要算法和关键问题。通过计算机模拟和波面实际测量,对十字路径积分法、傅里叶变换积分法和区域波前重构法三种主要算法的重建精度进行了对比研究。研究表明:区域波前重构法不但对高频噪声有较强的抑制作用,同时也可以处理复杂的连通区域和非等间距分布梯度数据的复杂情况,因此更适用于基于条纹反射术的波面测量。

数字散斑相关方法用于牙冠形状的三维测量

本文介绍了数字散斑相关方法用于牙冠形状的三维测量的过程。对于一个后牙牙冠的三维形状测量，我们首先测量该牙冠的五个面：颊面、舌面、近远中面、面，然后根据各测量面座标轴的相对位置关系，将五组局部数据转换到同一座标系中实现该牙冠的三维重建，并通过计算机绘图进行三维显示。该测量方法所获取的牙冠形状的三维数据为修复体CAD／CAM的实现奠定了数据基楚。本文还就该测量方法的特点、系统精度、三维重建中的数据结合方式、系统量程、可靠性等方面进行了讨论。

基于三维人体测量技术的女性乳房形态细分研究

人体体型细分是数字化服装生产和销售的前提,胸部形态结构是影响女装合体性和舒适性的关键因素.针对女性而言,即使是胸围、胸下围尺寸完全一致,胸厚、胸宽、乳房的耸、扁程度也有不同的差异.通过非接触式三维人体测量仪（TecMath）测量270名中国西部地区年龄在18～30岁之间的青年女性,对测量项目数据进行统计分析（聚类分析）,找到影响青年女性胸部特征的部位,同时将乳房形态细分为9类,为文胸等贴体内衣设计及服装量身定制提供技术参数.