非接触三维测量全场结构关系模型分析及系统开发

研究开发了一种基于光栅投影和主动式三角法的高精度三维测量系统。分析了系统的全场结构关系模型及镜头失真对系统的影响,给出了空间三维坐标的详细算法。试验结果表明,系统的测量误差小于0.04mm,测量精度约为0.03mm。多视角测量的拼合结果表明,系统具有良好的360°测量精度,测量精细表面纹理效果好。该系统在反求工程及质量控制等领域具有良好的工业应用前景。     

基于二维彩色靶标的结构光三维测量系统快速标定方法

系统标定是基于结构光投影的主动式光学三维面形测量的关键技术之一,同时也是一项复杂和耗时的工作。提出了一种基于RGB彩色模型的系统快速标定新方法。利用一个彩色的二维平面靶标和由投影仪投影的彩色标记特征图像实现了摄像机和投影仪的同时快速标定,对靶标的每个标定姿态位置只需要拍摄一幅图像即可得到该位置的特征参数。与传统方法相比,标定过程简单快捷,所需的数据量较少。利用该方法对一个结构光三维测量系统进行了现场标定,并测量了一个平面和一个半圆柱物体,实验结果中点到拟合平面的最大距离为0.8039mm,平均误差为0.1693mm。利用该系统恢复半圆柱物体的面形与传统标定方法的测量结果符合得很好。实验表明,由该方法获得的结果准确可用,且标定速度快。     

Calibration for stereo vision system based on phase matching and bundle adjustment algorithm

Calibration for stereo vision system plays an important role in the field of machine vision applications. The existing accurate calibration methods are usually carried out by capturing a high-accuracy calibration target with the same size as the measurement view. In in-situ 3D measurement and in large field of view measurement, the extrinsic parameters of the system usually need to be calibrated in real-time. Furthermore, the large high-accuracy calibration target in the field is a big challenge for manufacturing. Therefore, an accurate and rapid calibration method in the in-situ measurement is needed. In this paper, a novel calibration method for stereo vision system is proposed based on phase-based matching method and the bundle adjustment algorithm. As the camera is usually mechanically locked once adjusted appropriately after calibrated in lab, the intrinsic parameters are usually stable. We emphasize on the extrinsic parameters calibration in the measurement field. Firstly, the matching method based on heterodyne multi-frequency phase-shifting technique is applied to find thousands of pairs of corresponding points between images of two cameras. The large amount of pairs of corresponding points can help improve the accuracy of the calibration. Then the method of bundle adjustment in photogrammetry is used to optimize the extrinsic parameters and the 3D coordinates of the measured objects. Finally, the quantity traceability is carried out to transform the optimized extrinsic parameters from the 3D metric coordinate system into Euclid coordinate system to obtain the ultimate optimal extrinsic parameters. Experiment results show that the procedure of calibration takes less than 3 s. And, based on the stereo vision system calibrated by the proposed method, the measurement RMS (Root Mean Square) error can reach 0.025 mm when measuring the calibrated gauge with nominal length of 999.576 mm.     

Implementation and experimental study on fast object modeling based on multiple structured stripes

In this paper, a practical structured light-based system for fast object modeling and reconstruction is reported. The system consists of an off-the-shelf digital projector, a video camera and a turntable. The system calibration is implemented accurately and automatically by taking a single image of an illuminated calibration template. The multiple color light stripes emitted by the projector adopt only three colors and the color can be modified easily according to the surface texture of the object. This makes the system widely applicable in many situations, and the assumption about color neutrality, which is a limitation to other similar systems, can be largely relaxed. The registration and merging algorithm is greatly simplified by employing a turntable. The validity and high accuracy of the method are demonstrated by extensive real experiments.     

The effect of out-of-plane motion on 2D and 3D digital image correlation measurements

The effect of out-of-plane motion (including out-of-plane translation and rotation) on two-dimensional (2D) and three-dimensional (3D) digital image correlation measurements is demonstrated using basic theoretical pinhole image equations and experimentally through synchronized, multi-system measurements. Full-field results obtained during rigid body, out-of-plane motion using a single-camera vision system with (a-1) a standard f55mm Nikon lens and (a-2) a single Schneider–Kreuznach Xenoplan telecentric lens are compared with data obtained using a two-camera stereovision system with standard f55mm Nikon lenses.Results confirm that the theoretical equations are in excellent agreement with experimental measurements. Specifically, results show that (a) a single-camera, 2D imaging system is sensitive to out-of-plane motion, with in-plane strain errors (a-1) due to out-of-plane translation being proportional to ΔZ/Z, where Z is the distance from the object to the pin hole and ΔZ the out-of-plane translation displacement, and (a-2) due to out-of-plane rotation are shown to be a function of both rotation angle and the image distance Z; (b) the telecentric lens has an effective object distance, Z_eff, that is 50× larger than the 55 mm standard lens, with a corresponding reduction in strain errors from 1250 μs/mm of out-of-plane motion to 25 μs/mm; and (c) a stereovision system measures all components of displacement without introducing measurable, full-field, strain errors, even though an object may undergo appreciable out-of-plane translation and rotation.     

结构光三维测量系统中投影仪标定技术研究

投影仪标定是单摄像机单投影仪结构光三维测量中的基础。采用双面标定块实现投影仪的标定。标定块正面为黑底白色圆点图案,通过Tsai两步法及非线性优化完成摄像机标定。背面为反射率均匀的白色平面,由投影仪投影双方向高亮度的直线来生成特征点。针对特征点三维坐标难以确定的问题,采用了两种方法:一是依靠摄像机标定结果;二是结合正面圆点图案,利用交比不变性获取更多的有效输入数据。标定设备简单,操作方便。实验结果证明具有较理想的标定精度。     

Visualization of 3D variable in time object based on data gathered by active measurement system

The recent needs of analysis and visualization of variable in time real 3D objects in many applications require development of new approach towards combining rapid 3D shape acquisition and the methodology of data processing in order to perform visualization and analysis of real 3D dynamic objects. In this paper, the general concept of visualization system of data gathered by means of optical 4D (x,y,z,t) shape measurement system is presented. The concept of a virtual camera, as the mean for interactive object visualization is introduced. The experimental results for processing of simulated and real variable in time 3D object are presented and discussed. The directions of future works focused on full implementation of the concept are introduced.     

Fast 3D modeling in complex environments using a single Kinect sensor

Three-dimensional (3D) modeling technology has been widely used in inverse engineering, urban planning, robot navigation, and many other applications. How to build a dense model of the environment with limited processing resources is still a challenging topic. A fast 3D modeling algorithm that only uses a single Kinect sensor is proposed in this paper. For every color image captured by Kinect, corner feature extraction is carried out first. Then a spiral search strategy is utilized to select the region of interest (ROI) that contains enough feature corners. Next, the iterative closest point (ICP) method is applied to the points in the ROI to align consecutive data frames. Finally, the analysis of which areas can be walked through by human beings is presented. Comparative experiments with the well-known KinectFusion algorithm have been done and the results demonstrate that the accuracy of the proposed algorithm is the same as KinectFusion but the computing speed is nearly twice of KinectFusion. 3D modeling of two scenes of a public garden and traversable areas analysis in these regions further verified the feasibility of our algorithm.     

High-accuracy and real-time 3D positioning,tracking system for medical imaging applications based on 3D digital image correlation

This paper presents a system for positioning markers and tracking the pose of a rigid object with 6 degrees of freedom in real-time using 3D digital image correlation, with two examples for medical imaging applications. Traditional DIC method was improved to meet the requirements of the real-time by simplifying the computations of integral pixel search. Experiments were carried out and the results indicated that the new method improved the computational efficiency by about 4–10 times in comparison with the traditional DIC method. The system was aimed for orthognathic surgery navigation in order to track the maxilla segment after LeFort I osteotomy. Experiments showed noise for the static point was at the level of 10⁻³ mm and the measurement accuracy was 0.009 mm. The system was demonstrated on skin surface shape evaluation of a hand for finger stretching exercises, which indicated a great potential on tracking muscle and skin movements.     

基于大景深三维扫描系统对RAC标定法的修正

基于大景深三维扫描系统的倾斜摄像机模型,推导了新的物像关系并修正了Tsai的RAC标定法.利用修正后的RAC标定法对大景深扫描系统的摄像机进行了标定, 实验结果表明修正后的RAC标定法适用于倾斜的摄像机系统,标定准确度可以达到0.03 mm.     

光栅投影式三维肖像测量的关键技术

提出了一种在光栅投影式三维肖像测量系统中光栅投影平面的标定方法,讨论了该方法在应用中需要注意的问题。根据光栅投影式测量系统所获取的三维点群的特点,提出了基于线状分布的对三维测量点群进行曲面重建的方法,在对人物肖像的拟合应用中,既可确保所生成的三角形片形状良好,又可避免三维点的遗漏、曲面裂缝或形成孔洞,生成的三角片所逼近的人物肖像具有很好的连续性和光顺性。     

Differential 3D shape retrieval

We are presenting a differential three-dimensional (3-D) shape profiling method that is based on the combination of orthogonal fringe projection. It allows us to compute depth gradient maps in a fast and efficient manner. What we are demonstrating is that depth gradients can be computed in a simple way by measuring fringe deformation throughout a novel single-shot approach. We show the usefulness and potential applications of the proposed approach. Validation experiments are presented as well.     

基于3D结构光传感器的老龄人异常行为检测方法

针对多视角下老龄人异常行为检测问题,利用3D人体数据和多线性子空间分析方法,从时间、视角和空间动作特征对其进行了研究。首先通过三维结构光传感器获取人体扫描点云数据,并进行点云精简和人体表面重建。然后提取人体点云数据的表面曲率特征,并将其映射到二维彩色图像中,构成彩色动作特征图。通过提取特定时长内所有动作的彩色特征图,生成基于曲率的彩色动作能量图模型,并使用2D-PCA对彩色动作能量特征图进行降维。最后运用基于张量分析的多线性子空间分析方法,对多视角下降维后的数据进行视角无关的特征提取,并完成异常行为的分类和识别。实验结果表明,该方法切实可行,可将其应用于助老机器人和老龄人监护等相关领域。     

基于线结构光的双目三维体积测量系统

针对工业应用中工件的体积测量问题,设计了一个基于双目立体视觉原理的体积测量系统。线结构光投射到被测物表面产生变形的激光条纹,精确提取光条中心线,利用极线约束实现左右图像特征点匹配;根据双目视觉原理,由光条图像坐标计算出其在相机坐标系下的三维坐标,完成三维重建;将相机坐标系下的三维点云转换到理想的世界坐标系下,经过积分计算得到被测物体积。采用该系统对不规则棱锥实现三维重建,并完成体积测量。实验结果表明该方法具有一定的可行性和有效性,在工业检测领域有较好的应用前景。     

基于拟牛顿和遗传算法的三维人脸建模

用网格重采样算法和点变形技术把不同人脸纹理全景图进行标准化,实现三维人脸的像素级对齐;根据在不同姿态下用拟牛顿法优化目标函数优化速度的不同和提取的人脸特征点精确计算出输入图像中人脸的姿态;确定三维人脸模型在此姿态下的可见点,最后利用改进的实数遗传算法进行匹配计算,建立完整的三维人脸模型。实验表明,此算法能实现三维人脸像素级的精确对齐,快速的精确计算输入图像中人脸的姿态,减少优化参数,简化目标函数,提高模型匹配效率和重构精度,缩短匹配时间。     

Fringe projection based quantitative 3D microscopy

A fringe projection based quantitative three-dimensional microscopy (FP-3DM) is presented. The image formation for FP-3DM is formulated based on a concept of active micro stereovision. The problem of point correspondences in active stereo imaging can be solved with help of the phase measuring technique. A prototype of the FP-3DM is also established and calibration strategy for proposed FP-3DM is suggested. Some preliminary experiment results are also presented to verify this approach. The FP-3DM can provide quantitative 3D micro imaging especially for quantitative characterization of 3D microstructures.     

基于快速骨架提取的三维目标识别(英文)

针对三维目标识别问题,提出了一种基于快速骨架提取的方法。根据骨架所反映的目标拓扑结构,建立了不同目标局部结构之间的对应关系;而在对应的局部曲线段上,采用基于曲线配准的方法进行匹配;以各个局部匹配的成本之和评估不同目标的相似性.这种方法在目标出现一定程度的视觉变形时仍具有较好的识别效果,同时避免了基于曲线方法的匹配目标的局部,而忽略局部之间相互的空间组织的缺点所造成的误匹配.算例结果表明这种算法对于三维目标有较好的识别效果.     

基于快速骨架提取的三维目标识别

针对三维目标识别问题,提出了一种基于快速骨架提取的方法。根据骨架所反映的目标拓扑结构,建立了不同目标局部结构之间的对应关系;而在对应的局部曲线段上,采用基于曲线配准的方法进行匹配;以各个局部匹配的成本之和评估不同目标的相似性.这种方法在目标出现一定程度的视觉变形时仍具有较好的识别效果,同时避免了基于曲线方法的匹配目标的局部,而忽略局部之间相互的空间组织的缺点所造成的误匹配.算例结果表明这种算法对于三维目标有较好的识别效果.