Global Calibration Method of Multi-sensor Vision System Using Skew Laser Lines

Multi-sensor vision system plays an important role in the 3D measurement of large objects.However,due to the widely distribution of sensors,the problem of lacking common fields of view（FOV） arises frequently,which makes the global calibration of the vision system quite difficult.The primary existing solution relies on large-scale surveying equipments,which is ponderous and inconvenient for field calibrations.In this paper,a global calibration method of multi-sensor vision system is proposed and investigated.The proposed method utilizes pairs of skew laser lines,which are generated by a group of laser pointers,as the calibration objects.Each pair of skew laser lines provides a unique coordinate system in space which can be reconstructed in certain vision sensor＇s coordinates by using a planar pattern.Then the geometries of sensors are computed under rigid transformation constrains by taking coordinates of each skew lines pair as the intermediary.The method is applied on both visual cameras with synthetic data and a real two-camera vision system;results show the validity and good performance.The prime contribution of this paper is taking skew laser lines as the global calibration objects,which makes the method simple and flexible.The method need no expensive equipments and can be used in large-scale calibration.

Calibration method for multi-line structured light vision sensor based on Plücker line

For the rapid calibration of multi-line structured light system,a method based on Plücker line was proposed.Most of the conventional line-structured light calibration methods extract the feature points and transform the coordinates of points to obtain the plane equation.However,a large number of points lead to complicated operation which is not suitable for the application scenarios of multi-line structured light.To solve this issue,a new calibration method was proposed that applied the form of Plücker matrix throughout the whole calibration process,instead of using the point characteristics directly.The advantage of this method is that the light plane equation can be obtained quickly and accurately in the camera coordinate frame.Correspondingly a planar target particularly for calibrating multi-line structured light was also designed.The regular lines were transformed into Plücker lines by extending the two-dimensional image plane and defining a new image space.To transform the coordinate frame of Plücker lines,the perspective projection mathematical model was re-expressed based on the Plücker matrix.According to the properties of the line and plane in the Plücker space,a linear matrix equation was efficiently constructed by combining the Plücker matrices of several coplanar lines so that the line-structured light plane equation could be furtherly solved.The experiments performed validate the proposed method and demonstrate the significant improvement in the calibration accuracy,when the test distance is 1.8 m,the root mean square(RMS)error of the three-dimensional point is within 0.08 mm.

Calibration of line structured light vision system based on camera’s projective center

Based on the characteristics of line structured light sensor, a speedy method for the calibration was established. With the coplanar reference target, the spacial pose between camera and optical plane can be calibrated by using of the camera’s projective center and the light’s information in the camera’s image surface. Without striction to the movement of the coplanar reference target and assistant adjustment equipment, this calibration method can be implemented. This method has been used and decreased the cost of calibration equipment, simplified the calibration procedure, improved calibration efficiency. Using experiment, the sensor can attain relative accuracy about 0.5%, which indicates the rationality and effectivity of this method.

Analysis of the Design and Application of a Novel CT Secondary Cable Line Calibrator

With the rapid development of electrical power systems,ensuring the accuracy and reliability of power transmis-sion has become particularly crucial.The secondary cable line calibrator for current transformers(CT)plays an essential role in calibrating electrical power systems.It is not only related to the safe operation of the system but also directly im-pacts the accuracy of energy metering.This study aims to design and analyze an efficient CT secondary cable line calibra-tor to explore its application effects in the power system.By thoroughly analyzing the characteristics of CT secondary ca-ble lines and the design requirements of the calibrator,this paper proposes an innovative design scheme for the calibrator.This device demonstrates significant effects in enhancing the accuracy and stability of power system calibration,providing robust technical support for the optimization and upgrade of the power system.This research not only offers a theoretical basis and practical guidance for the design and application of CT secondary cable line calibrators but also contributes new ideas and methods for the precise calibration and efficient management of the power system.

Novel camera calibration method based on invariance of collinear points and pole-polar constraint

To address the eccentric error of circular marks in camera calibration,a circle location method based on the invariance of collinear points and pole–polar constraint is proposed in this paper.Firstly,the centers of the ellipses are extracted,and the real concentric circle center projection equation is established by exploiting the cross ratio invariance of the collinear points.Subsequently,since the infinite lines passing through the centers of the marks are parallel,the other center projection coordinates are expressed as the solution problem of linear equations.The problem of projection deviation caused by using the center of the ellipse as the real circle center projection is addressed,and the results are utilized as the true image points to achieve the high precision camera calibration.As demonstrated by the simulations and practical experiments,the proposed method performs a better location and calibration performance by achieving the actual center projection of circular marks.The relevant results confirm the precision and robustness of the proposed approach.

Sub-pixel extraction of laser stripeand itsapplication in laser plane calibration

For calibrating the laser plane to implement 3D shape measurement, an algorithm for extracting the laser stripe with sub-pixel accuracy is proposed. The proposed algorithm mainly consists of two stages： two-side edge detection and center line extraction. First, the two-side edge of laser stripe is detected using the principal component angle-based progressive probabilistic Hough transform and its width is calculated through the distance between these two edges. Secondly, the center line of laser strip is extracted with 2D Taylor expansion at a sub-pixel level and the laser plane is calibrated with the 3D reconstructed coordinates from the extracted 2D sub-pixel ones. Experimental results demonstrate that the proposed method can not only extract the laser stripe at a high speed, nearly average 78 ms/frame, but also calibrate the coplanar laser stripes at a low error, limited to 0.3 mm. The proposed algorithm can satisfy the system requirement of two-side edge detection and center line extraction, and rapid speed, high precision, as well as strong anti-jamming.

Refined empirical line method to calibrate IKONOS imagery

To extract quantitative biophysical parameters such as leaf biomass and leaf chlorophyll concentration from the remotely sensed imagery, the effect of atmospheric attenuation must be removed. The refined empirical line （REL） method was used to calibrate the IKONOS multispectral imagery. The IKONOS digital numbers （DN） were converted to the at-satellite reflectance, then the linear relation between at-satellite reflectance and surface spectral reflectance （ρA） was derived from six bright targets of known reflectance in the image, and modelled estimates of the image reflectance at ρA=0. Validation targets were used to test the feasibility of REL method. The mean relative errors between ρA retrieved from IKONOS image using REL method and ground-measured ρA were 11%, 13%, 3% and 5% in the IKONOS blue, green, red and near-infrared （NIR） respectively. When dark targets are unavailable or measurement of dark target is inconvenient, the REL method was most crucial for retrieving surface spectral reflectance. The REL offers a simple approach for quantitative retrieval of biophysical parameters from IKONOS imagery.

Empirical Line Method Using Spectrally Stable Targets to Calibrate IKONOS Imagery

By using speetrally stable targets, the empirical line （EL） method was tested to correct the multispectral IKONOS imagery acquired over Putuo Mountain, Zhejiang, China. A series of calibration targets, which were spectrally stable over time, were selected to establish the linear predicted equation. Subsequently, a series of spectrally stable validation targets were selected to assess the accuracy of the equations. And, validation targets, which were speetrally unstable over time, were used to test the feasibility of using the EL method to calibrate the archival remotely sensed data. Ground reflectance measurements for each target were made using an ASD FieldSpec spectroradiometer. A Trimble GeoXTTM GPS unit with sub-meter accuracy was used to estimate the target position accurately. Linear regression equations for four tKONOS bands were derived. The coefficients of determination for the blue, green, and red bands were all greater than 0.9800 and it was 0.9697 for the near infrared band. It was concluded that reasonable results could be obtained by using speetrally stable targets.

High-speed VUV spectroscopy for edge impurity line emission measurements in HL-2A tokamak

A 20 cm focal length normal incidence vacuum ultraviolet （VUV_20 cm） monochromator with a fast time response has been developed for measuring edge impurity line emission in the wavelength range of 300-2000 A on an HL-2A tokamak. An aberration corrected concave holographic grating with 1200 grooves/mm is adopted in the monochromator, which provides a wavelength dispersion of 40 A mm-1. The aperture is f/4.5. A channel electron multiplier is used as a detector. The time resolution of the system is 17 μs. Wavelength calibration of the system has been done by using a hollow cathode light source in the laboratory with helium and argon gases. The obtained signals of helium and argon spectra are very strong since the inner surface of the monochromator vacuum chamber is blackened and the stray light level is then significantly reduced. The optical property of the system has been examined by scanning the width of the entrance and exit slits. The system is then installed at the mid-port of the HL-2A tokamak and typical line emissions from the HL-2A plasma are measured. Time behaviors of edge impurity line emissions are observed with the fast time response system in different plasma confinement regimes, especially in the H-mode discharges. The result shows that the VUV_20 cm system works very well to measure the edge impurity line emissions in the edge localized modes phase of H-mode discharges.

A fast and precise three-dimensional measurement system based on multiple parallel line lasers

This paper conducts a trade-off between efficiency and accuracy of three-dimensional(3 D)shape measurement based on the triangulation principle,and introduces a flying and precise 3 D shape measurement method based on multiple parallel line lasers.Firstly,we establish the measurement model of the multiple parallel line lasers system,and introduce the concept that multiple base planes can help to deduce the unified formula of the measurement system and are used in simplifying the process of the calibration.Then,the constraint of the line spatial frequency,which maximizes the measurement efficiency while ensuring accuracy,is determined according to the height distribution of the object.Secondly,the simulation analyzing the variation of the systemic resolution quantitatively under the circumstance of a set of specific parameters is performed,which provides a fundamental thesis for option of the four system parameters.Thirdly,for the application of the precision measurement in the industrial field,additional profiles are acquired to improve the lateral resolution by applying a motor to scan the 3 D surface.Finally,compared with the line laser,the experimental study shows that the present method of obtaining 41220 points per frame improves the measurement efficiency.Furthermore,the accuracy and the process of the calibration are advanced in comparison with the existing multiple-line laser and the structured light makes an accuracy better than 0.22 mm at a distance of 956.02 mm.

一种角向传输线B-dot标定平台的设计

基于感应电压叠加器感应腔角向传输线电流探头离线标定的需求,设计了离线标定平台。离线标定平台为平板传输线结构,与在线标定相比,对标定信号的畸变更低。分析了跨平台标定误差的来源,并针对性提出降低误差的措施。分析表明,安装偏心及探头纵向安装深度是跨平台标定误差的最大来源,需要在工程设计中重点关注。实际建立了离线标定平台并开展误差分析,得到跨平台标定误差3.3%的结果。

基于近红外光谱模型转移的牛奶蛋白检测方法研究

目的研究基于近红外光谱模型转移的牛奶蛋白检测方法。方法分别采用实验室与在线检测近红外光谱仪采集生产过程中原料奶样品的近红外光谱,研究斜率截距法(slope/bias,S/B)、分段直接标准化(piecewise direct standardization,PDS)算法、Shenk’s方法在不同仪器测量光谱之间模型转移应用,优化模型参数,提高实验室仪器建立的校正模型应用于在线光谱仪器的预测精度。结果经过Shenk’s算法转移,主从机的光谱平均差异降低为0.0075,光谱校正率达到98.95%。利用模型转移方法与偏最小二乘模型结合,将实验室分析光谱仪建立的模型用于生产在线光谱仪测量光谱预测,显著提高了牛奶中蛋白质含量预测准确度,不同仪器之间模型预测相对均方根误差从5.52%下降到2.03%。结论本研究的方法实现了实验室分析与在线检测仪器测量光谱及定量分析模型转移共享,为近红外在线检测的智能化改进提供了基础。

薄膜热流计与原子层热电堆热流传感器的激波风洞试验对比

激波风洞试验的主要测试量是热流密度,且多采用薄膜热流计进行测试,但薄膜热流计热流测试结果缺乏直接验证手段,存在测热结果不确定度偏大等问题。原子层热电堆(ALTP)热流传感器响应时间短且线性度好,结合高精度可溯源的热流传感器标定实验,可保证ALTP热流传感器测热结果的准确性和可靠性。在多个流场条件下的激波风洞试验中开展了薄膜热流计和ALTP热流传感器测热结果交叉对比验证。对比试验显示:ALTP热流传感器和薄膜热流计在不同流场参数下测热结果相对稳定,中高热流下两者测热结果相差在8%以内。结合对比标定溯源链以及激波风洞试验测热结果的讨论,展现了利用ALTP热流传感器在激波风洞试验中在线标定薄膜热流计的可行性。

基于线结构光的大型构件表面尺寸加工质量检测方法

针对大型构件表面尺寸加工质量的高精度三维检测的需求,设计了一套主动式线结构光旋转扫描检测系统.采用相机主动式旋转扫描,适用于不方便移动且跨距大、特征多的大型构件检测.提出了一种新的系统旋转中心快速标定的方法,仅需标靶上一点即可完成标定,适合大型构件检测的现场快速标定.加入编码机构,可根据被测物的特征变化动态调整扫描速度,提高了系统检测效率和通用性.所有元器件均可单独调用,保证了系统的可扩展性.改善了扫描时的串口逻辑,进一步提高了三维点云的密度.实验结果表明,本系统对标准物体的最大偏差为0.0310 mm,标准差最大为0.0150 mm,对大型构件实物的检测误差在0.05 mm以内,满足大型构件表面特征加工质量的高精度三维检测需求.

大范围生态保护红线定标布局方法

生态保护红线勘界定标是生态保护红线划定落实之后的又一项重要工作,是常态化监管的基础和前提。当前,生态保护红线勘界定标处于摸索试点阶段,国家层面缺乏具体指导细则,省市作为生态保护红线勘界定标工作的责任主体,只能结合实地因地制宜开展,缺乏系统性、标准性。定标布局是勘界定标的关键环节,主要解决生态保护红线区域内界桩和标识牌的数量确定、拟埋设位置选择等问题。本文提出一种大范围生态保护红线定标布局方法,先将生态保护红线区域按一定尺度划分为格网单元,筛选出涉及生态保护红线边界的格网单元,再引入行政区域、人口数量、道路交通、地形类别等特征因子构建度量模型,进一步开展度量特征计算,根据特征阈值最终选定格网单元,并以最终选定的格网单元作为定标布局方案,指导界桩和标识牌数量设定及埋设点位选址。以重庆市为例开展大范围生态保护红线定标布局应用,为重庆全市域生态保护红线勘界定标工作提供了第一手资料,同时,验证了本文方法在指导省市实施生态保护红线定标布局的科学性和实用性。

基于线结构光的零件三维尺寸测量系统

针对原有接触式三维测量技术测量时间长、效率低、对零件有损伤等问题,提出一种基于线结构光的零件三维尺寸测量系统。建立光平面数学模型,采用基于平面靶标的自由移动标定法标定光平面,利用基于Hessian矩阵的Steger方法对线结构光中心提取,通过坐标变换得到零件的三维尺寸。在Visual Studio软件中的Winform窗体应用设计三维测量系统的软件交互界面,搭建实验测量平台进行多个零件的测量实验。实验结果表明,对不同零件三维尺寸测量相误差均小于4%,提出的测量系统及方法具有较高的精度和稳定性,能够满足工程应用。

基于四面体特征的面阵激光雷达与相机标定方法

为了提高面阵激光雷达与相机标定精度,提出了一种基于四面体结构的面阵激光雷达与相机标定方法。利用图像中角点的反投影射线和点云中直线特征建立“点-三线”的对应关系,提高了约束强度,根据异面直线间的距离和投影直线间的夹角建立约束方程,通过非线性优化求解相机和雷达坐标系间的变换向量并最终得到变换矩阵。构建三角板和地面组成的四面体结构并进行实验验证,实验结果表明:该方法的平均投影误差在0.6像素以内,优于其他两种标定方法,为后续激光雷达数据与图像数据融合提供了研究基础。

基于2.5D标定扇的线阵相机内参数标定方法

针对工业生产线上或集成设备中线阵相机内参数定期检校困难且成本高的问题,提出一种基于2.5D标定扇的线阵相机内参数标定方法。设计了一款特定的2.5D标定扇,构建包含镜头畸变的线阵相机内参数标定模型,顾及了标靶相对相机的两个姿态角,通过方程线性变换法解算模型参数初值,利用改进的Levenberg-Marquardt(L-M)算法加速优化相机参数的求解过程,给出了详细的解算步骤和数据处理过程,并通过仿真和实测数据验证了方法的可行性。结果表明:该线阵相机标定方法简单灵活,可得到大量分布规律的特征点对,参数标定精度不受相机移动精度和特定移动方向的限制;在扇骨面与靶面间夹角小于10°时,可以获得高精度、高一致性的相机内参数,特征点重投影误差的最大值优于0.28 pixel,平均RMSE为0.11 pixel,标准差仅0.01 pixel。

可见光光谱辐射计波长标定技术研究

为了解决可见光光谱辐射计波长标定过程中存在的峰值偏移、较弱特征谱误判及人工谱线识别等问题,采用自适应阈值法和差分法完成对特征谱检测与识别,利用最小二乘法和拉格朗日插值法确定波长和像元的关系,进行了理论分析和实验验证,获得最佳波长标定方程。结果表明,特征谱根据谱线强度依次被检测并识别出来,以404.6565 nm、435.8335 nm、546.0750 nm、579.0670 nm为基准的拉格朗日插值法得到的方程为最佳波长标定方程,其残差标准差仅为3.2747×10^(-13)nm,波长标定误差分布在±0.2 nm范围内。自动谱线检测方法及谱线识别方法提高了波长标定效率,避免了噪声误判和谱线识别错误现象,为其它光谱类仪器的波长标定提供了参考。

基于单目视觉的无水尺水位测量方法

水位是水文监测的关键要素,其精准测量对洪涝灾害防御和水量计量具有重要的意义。随着智慧水利建设和视频设备的大规模部署,基于图像处理的水位识别方法发展迅速,是目前水利量测领域的前沿方向。本文提出了一种基于单目视觉的无水尺水位测量方法。该方法采用深度学习构建水面分割模型,自动从水岸图像中提取水位线;再根据相机标定得到的空间映射关系,结合断面约束,计算水位线像素坐标对应的三维空间坐标,进而处理得到水位值。该方法应用于室内河工模型水槽实验,水面分割准确,水位线平均错误分割像素个数为0.825,计算水位值的平均绝对误差约为1.5 mm,均方根误差约为1.9 mm。实验结果表明该方法准确测量了水位的变化过程。