三阶段局部双目光束法平差视觉里程计

针对光束法对初始值依赖性大以及双目相机模型的特点,在ORB-SLAM2算法基础提出了一种三阶段局部双目光束法平差算法。在帧间位姿跟踪阶段,为降低累积误差对匀速模型下3D-2D匹配的影响,引入环形匹配机制进一步剔除误匹配,并将关键帧地图点与当前帧3D-2D投影匹配;在跟踪局部地图阶段插入关键帧时,增加双目相机基距参数优化环节;在局部地图优化阶段,将最近的两关键帧间的普通帧也作为局部帧进行优化。KITTI数据集实验表明,三阶段局部双目光束法平差与ORB-SLAM2相比,构造了更多精确的3D-2D匹配,增加了优化约束条件,提高了运动估计与优化精度。     

跟踪式偏振光三角法测头

针对三角法测量的不足,设计了一种跟踪式偏振光三角法测头。对三角测量法的理论分析表明减小测量范围能提高测量精度。测头结合表面跟踪方法与三角测量法,跟踪使测量范围不受限制;仅在小范围内进行三角法测量,测量精度大大提高。对金属表面的反射特性进行了分析和推导,得出镜面反射与漫反射具有不同的偏振特性。通过偏振滤光减少了镜面反射光对测量的影响,从而降低了对被测表面材质的要求。本文给出了测头结构和工作原理。试验表明,测头能测量镜面反射较强的金属表面,测头可自动跟踪表面,并可结合测距仪实现表面形状的高精度测量。     

Unification scheme for 3D surface reconstruction using physically based models

We propose a unification framework for three-dimensional shape reconstruction using physically based models. A variety of 3D shape reconstruction techniques have been developed in the past two decades, such as shape from stereopsis, from shading, from texture gradient, and from structured lighting. However, the lack of a general theory that unifies these shape reconstruction techniques into one framework hinders the effort of a synergistical image interpretation scheme using multiple sensors/information sources. Most shape-from-X techniques use an “observable” (e.g., the stereo disparity, intensity, or texture gradient) and a model, which is based on specific domain knowledge (e.g., the triangulation principle, reflectance function, or texture distortion equation) to predict the observable, in 3D shape reconstruction. We show that all these “observable–prediction-model” types of techniques can be incorporated into our framework of energy constraint on a flexible, deformable image frame. In our algorithm, if the observable does not confirm to the predictions obtained using the corresponding model, a large “error” potential results. The error potential gradient forces the flexible image frame to deform in space. The deformation brings the flexible image frame to “wrap” onto the surface of the imaged 3D object. Surface reconstruction is thus achieved through a “package wrapping” or a “shape deformation” process by minimizing the discrepancy in the observable and the model prediction. The dynamics of such a wrapping process are governed by the least action principle which is physically correct. A physically based model is essential in this general shape reconstruction framework because of its capability to recover the desired 3D shape, to provide an animation sequence of the reconstruction, and to include the regularization principle into the theory of surface reconstruction.     

Measurement based on fringe reflection for testing aspheric optical axis precisely and flexibly

A method based on fringe reflection is proposed to measure the optical axis of an aspheric mirror precisely and flexibly. In the measurement, a screen displaying a fringe pattern is moved along its normal direction, and a camera is located beside and observes the fringe pattern reflected via a tested surface. This method can test the optical axis of an aspheric mirror quantitatively before measuring the absolute height of the tested surface. And it can be combined with some presented methods that need to fit the aspheric mirror according to the optical axis to measure the surface. To validate the ability of this method, it is combined with one of the presented methods to measure absolute height of an aspheric mirror precisely and flexibly. Computer simulations and preliminary experiment validate the feasibility of this method.     

由序列图像进行三维测量的新方法

目前的三维测量方法都需要专门的测量设备且存在着种种限制,为此提出了一种基于图像序列进行三维测量的新方法。将由数码相机围绕被测物体拍摄的多幅图像导入计算机,利用图像处理知识得到特征的二维信息;采用计算机视觉方法,对特征从射影空间到欧式空间分层逐步重建即可完成三维测量。设计一套特征标志组合,作为辅助测量工具避免了特征匹配难题。确立了一套图像分割与识别策略获得特征标志二维信息,识别率可达到95%以上。采用基于模约束的摄像机分层自标定方法得到特征在欧式空间下的三维信息,并通过多种优化方法减少误差的影响。该方法在硬件上实现简单,对测量条件要求不高。实际试验表明,相对误差可达到1.48%,重投影误差为0.3864像素。     

多目视觉测量系统的光束法平差改进

为了消除三维扫描测量机器人系统中工业机器人定位误差对测量结果的不利影响,搭建了多目视觉测量系统对三维扫描测头进行空间同步定位.由于系统中相机与标志点之间的距离变化较大,标志点重投影误差难以评价空间定位误差,另外受相机标定精度影响,光束法平差对三维坐标修正不明显.为解决上述问题,本文改进了光束法平差,在传统光束法平差的误...     

基于光束法平差单点三坐标测量的新方法

在研究多组像片内方位元素的修正和全局光束法平差的基础上,提出使用3台像机同时对测棒进行数据采集,通过光束法平差实现单点三坐标测量的新方法,并完成系统硬件的组建。通过实验,将新系统测量的结果与计量型三坐标仪测量值进行比较,得到系统的相对测量精度高于129061,优于单、双像机系统,能够满足工业产品的检测需求。     

Intermittent process hybrid measurement system on the machining centre

This study introduces the development of a hybrid measurement system integrated on a machining centre to carry out the possible intermittent measurement of a workpiece. The developed hybrid measurement system principally consists of a MP10 touch trigger probe system, a circular triangulation laser probe system, and the measurement software. The touch trigger probe system was primarily used to measure the regular geometric features, whereas the circular triangulation laser probe system was adopted to inspect the freeform surface part of a test carrier with the help of the developed measurement software. An adjustment device consisting mainly of an adjustment unit, a joint unit, and an assembly unit, was designed and manufactured to minimize the cosine error caused by the assembly inaccuracy for the laser probe. The measuring uncertainty analysis experiments for both the touch trigger probe system and the non-contact laser probe system were investigated by using a calibrated standard sphere and the HP5529A laser interferometer system, respectively. The information in the whole measuring system – which comprised a personal computer, a CNC machining centre controller, a Renishaw MP10 touch probe system, and the controller of a Wolf & Back OTM3A20 circular triangulation laser probe system – was integrated technically. The measurement software was also developed to simulate the measuring path, prevent collision, and generate the corresponding measuring NC codes. The developed system can also be used to digitize the data points of a 3D small complex workpiece, such as a tooth model and an IC part. A carrier, combined with free form surface and regular geometric feature referred to in the ISO 10791-7 cutting test standard, was designed, manufactured and inspected in order to evaluate the performance of the developed hybrid measuring system. The measurement results of this carrier were verified through a CNC coordinate measuring machine, with satisfactory consistency. According to the measuring results, the developed hybrid measuring system was successfully and effectively used to carry out the intermittent measurement.     

一种平面标靶的校正方法

提出一种新的标靶校正方法.首先,用一台数码相机从不同角度拍摄标靶,获取多幅图像.分别提取各图像中标志点的中心作为特征点,根据标靶图案的拓扑关系,建立各幅图像间同名标志点的对应关系,并结合光束平差计算特征点的三维坐标,该特征点的三维坐标由尺度因子所约束.最后,根据任意两个特征点的实际距离来获取尺度因子,并将各特征点的三维...     

激光三角法距离传感：散斑的影响

描述了一个激光三角法距离传感，并用于鞋楦三维测量。讨论了系统的静态和动态测量误差，指出其深度分辨率主要由散斑决定，实验表明 ，增加透镜孔径或在成象透镜前加一随机振动位相掩膜均可极大改善深度分辨率。     

环形子孔径检测技术中测量数据的准确提取方法

环形子孔径拼接测试技术是一种无需辅助元件就能检测旋转对称大口径非球面镜的有效手段。根据该技术的检测原理及基于Zemike多项式的“拼接”算法,提出了一种相应的环形子孔径数据提取方法。该方法基于商用相移干涉仪的CCD成像系统和其数据处理软件提供的Mask编辑功能,利用被测镜面上方的三个可移动的基准标记进行绝对定位,给出了具体的实施方案。对一口径700mm、F2的抛物面主镜进行实验,研究结果表明,该数据提取方法操作简单可行,适合于加工车间的实施,取得了符合“拼接”算法需求的子孔径测试数据和对应环带的内外半径值。     

一种新的模板匹配算法及其在三维形貌测量中的应用

投影光栅法是进行三维形貌测量的有效手段，但当被测物体陡峭度较大或存在高度突变时会出现阴影问题。为此本提出一种基于互相关函数差值的模板匹配算法，该算法可以有效地解决这一问题，同时该算法也可用于大尺度物体三维形貌测量的拼接技术，中给出了算法的详细描述及实例计算，计算结果证明了该算法的正确性。     

Flying triangulation--an optical 3D sensor for the motion-robust acquisition of complex objects

Three-dimensional (3D) shape acquisition is difficult if an all-around measurement of an object is desired or if a relative motion between object and sensor is unavoidable. An optical sensor principle is presented-we call it "flying triangulation"-that enables a motion-robust acquisition of 3D surface topography. It combines a simple handheld sensor with sophisticated registration algorithms. An easy acquisition of complex objects is possible-just by freely hand-guiding the sensor around the object. Real-time feedback of the sequential measurement results enables a comfortable handling for the user. No tracking is necessary. In contrast to most other eligible sensors, the presented sensor generates 3D data from each single camera image.     

A high-accuracy monocular self-calibration method based on the essential matrix and bundle adjustment

Accurate camera calibration is necessary in photogrammetry systems. While traditional calibration methods need precise calibration pattern, this paper introduces a high-accuracy self-calibration method that doesn’t need any metric information of the scene. The proposed method combines epipolar geometry and bundle adjustment, and both intrinsic and extrinsic parameters are obtained. Synthetic data as well as real data have been used to test the method, and the simulation result shows that the mean absolute relative calibration errors of the focal lengths and the principal point are about 4.5e-4 and 8e-4, respectively, under zero-mean Gaussian noise with 0.1 pixels standard deviation. Compared with existing calibration methods, the proposed method is cost-effective and simple with comparable accuracy.     

Telecentric three-dimensional sensor with a liquid mirror for large-object inspection

We describe a device that applies the advantages of the space invariance of telecentric triangulation with the measurement of large objects (1 m(3)). Because the scan motion of the laser beam is decoupled from the physical transport of the sensor head, the fast scanning of large volumes becomes feasible. The device consists of a triangulation laser telemeter head that uses a large liquid primary mirror and an aspheric secondary mirror to realize the telecentric f-theta objective. We propose using liquid-mirror technology to make low-cost large objectives that have low f numbers, a diffraction-limited performance, and low scattering in the visible. This new optical system is useful for 3-D measurement. We discuss the optical configuration of the system and the performance of a laboratory prototype. The prototype has a standoff distance of 1.5 m, a telecentric scan as long as 1 m, a depth of view of 1 m, and a relative depth resolution of 0.5-1 mm.     

基于Delaunay三角剖分的层析图像离散数据表面重建算法

提出一种基于Delaunay三角剖分思想的层析图像离散数据的表面重建算法。该算法考虑了组成最优重建表面的三角片的形态特点,以三角片集的内角矢量最大为优化目标,根据Delaunay三角剖分思想,采用局部判定的方法,逐次选取最佳几何形态的三角片,组成最优的重建表面。     

基于多视图立体视觉的沙堆三维尺寸测量研究

利用从运动中恢复结构方法(SFM),提出了一种基于多视图立体视觉的沙堆三维重建及三维尺寸测量方法。首先根据SFM方法的求解不稳定特点,结合光束平差法对SFM求解过程进行分析及优化;其次针对SFM重建结果为稀疏点云的问题,利用基于面片的稠密重建算法重新生成稠密的三维点云,再利用泊松算法对密集点云进行三维曲面重建;最后获得模型的三维尺寸信息。对某建筑工地的沙堆进行了三维尺寸的测量实验,实验结果验证了该方法的有效及可行性,提高了重建能力及精度,同时考虑了目标实际测量误差与重建误差,能够满足实际智能测量的应用需求。     

无人飞艇低空数码影像多视摄影测量

针对大比例尺测图的精度要求,研究低空数码影像多视摄影测量的方法.根据计算机视觉的多视几何原理建立匹配的约束条件,实现多视匹配;利用低空数码影像的重叠度大的特点,建立多基线立体,进行多片空间前方交会.不同重叠度的立体像对空间前方交会和多片空间前方交会的实验结果证明,多视摄影测量能够提高有效低空数码影像的摄影测量精度.     

基于近景数字摄影的坐标精密测量关键技术研究

研究了基于数字近景摄影原理的三维坐标精密视觉测量方法，可用于工业现场大尺寸范围内的坐标测量。对其核心技术，即数字成像器件高精度模型及标定、成像器件空间精密定向、高精度亚像素图像处理算法以及光学编码与精密测头技术，进行了深入的讨论，给出了原理和实现思路，为工业现场数字近景摄影三维坐标精密测量系统的设计提供了理论依据。     

Novel method of calibration with restrictive constraints for stereo-vision system

Regarding the calibration of a stereo vision measurement system, this paper puts forward a new bundle adjustment algorithm based on the stereo vision camera calibration method. Multiple-view geometric constraints and a bundle adjustment algorithm are used to optimize the inner and outer parameters of the camera accurately. A fixed relative constraint relationship between cameras is introduced. We have improved the normal equation construction process of the traditional bundle adjustment method, so that each iteration process occurs just outside the parameters of two images that are taken by a camera that has been optimized to better integrate two cameras bound together as one camera. The relationship between the fixed relative constraints can effectively increase the number of superfluous observations of the adjustment system and optimize higher accuracy while reducing the dimension of the normal matrix; it means that each iteration will reduce the time required. Simulation and actual experimental results show the superior performance of the proposed approach in terms of robustness and accuracy, and our approach also can be extended to stereo-vision system with more than two cameras.