Special issue-“Optical 3D measurement technology”
2019, 48(5): 503001.
doi: 10.3788/IRLA201948.0503001
Aiming at the problem that it was difficult to achieve large-scale and high-precision 3D reconstruction of land form of geomorphology by visual method in deep-sea environment, a design scheme of line structured light 3D reconstruction vision sensor for deep-sea topography features based on Jiaolong manned submersible was presented. According to the principle of 3D reconstruction of linear structured light, firstly, the Steger algorithm was improved to extract the center line of laser fringes quickly and accurately, then direct calibration method was used to solve the 2D spatial coordinates of topographic features, and the influence of image distortion on reconstruction was overcame. Then, the obtained 2D point cloud was fused with multi-sensor data, and the offset was calculated in real time according to the coordinates of the submersible, and the image was corrected according to the change of sensor position and attitude. Finally, the 3D point cloud data of landform was obtained. According to the reconstruction principle, the hardware and software system of the vision sensor was designed, and an experimental simulation platform was built to verify the feasibility of the scheme. Through underwater experiments, the complete reconstruction of simulated geomorphology can be achieved, with an accuracy of 96.9%, which meets the reconstruction requirements.
Aiming at the characteristics of large-scale, high-resolution, high-efficiency, complex structure of large component shape measurement in aerospace and marine manufacturing filed, a method for measuring the high-resolution geometric shape of large components was proposed, based on the optic-electrical scanning and positioning theory combined terminal shape measurement technology. The fringe projection photogrammetry system was used to project phase fringes on the local surface of the component to obtain high-precision dense point cloud, the pose measurement algorithm was designed to solve the problem that the pose measurement cannot be realized when the complex scene does not meet the intersection condition, the position of fringe projection photogrammetry system in the global measurement network system established by the workshop measurement positioning system(wMPS) can be measured. Therefore, the overall shape measurement of large components was completed through data fusion without relying on the software splicing algorithm. The experimental results show that the point cloud density of the system is 50 points/mm2, and the overall measurement accuracy of the system can reach 0.22 mm.
2019, 48(5): 503003.
doi: 10.3788/IRLA201948.0503003
The security of electronic payment has become an urgent problem. A secure Quick Response(QR) code system was proposed based on the technology of three-dimensional(3D) imaging and 3D authentication information. Firstly, the integral imaging technology was used to generate 3D digital watermark as the logo of the merchant. Secondly, identity based digital signature was carried out. Then, in the Fresnel domain, the 3D digital watermark with signature information was carried by using a secure QR code system, which was then compressed and hidden in the QR code. Finally, the users scan QR code to identify and extract the hidden data. If the signature information of verification was confirmed by users, the algorithm of reconstruction was executed, and the 3D digital watermark images were displayed. The payments were confirmed after the users were authenticated. The process of interactive authentication was completed. According to the results of experiments, the schemes can effectively prevent the 3D digital watermark from being tamper-bent, falsified, and unjustified. The proposed method not only enhances the security of scanning mobile payment, but also improves the real-time and convenience of the system. When multiple parameters of the proposed system are combined as keys, the dimensions of keys are effectively increased. The key space is broadened. The difficulty of illegal attack is enhanced, and the safety and stability of the system are improved too. It can protect the security of personal fund, and also maintain the reputation and property security of enterprises.
2019, 48(5): 503004.
doi: 10.3788/IRLA201948.0503004
The three-dimensional scanning LiDAR can actively acquire three-dimensional information of target. High-speed data acquisition and transmission are key technical issues for three-dimensional real-time imaging. A ground-based three-dimensional scanning LiDAR was designed using data acquisition and control system to achieve three-dimensional imaging with point cloud. The LiDAR hardware design included a transmitting and receiving unit, a ranging unit, and a scanning unit for acquiring the three-dimensional point cloud data of the target. The software design of the LiDAR included upper computer program, lower computer program and USB firmware program design for accomplishing point cloud data acquisition, data transmission, data storage, data analysis and real-time imaging which were collected in lower computer and transmitted into upper computer. Through multiple scene experiments, the results show that three-dimensional scanning LiDAR system has a centimeter-level ranging error, which can realize three-dimensional real-time imaging.
2019, 48(5): 503005.
doi: 10.3788/IRLA201948.0503005
When a flight flies at high speed in the atmospheric, aerodynamic heating, the optical window interacts with the external airflow to form a complex flow field structure. Its refractive index distribution was irregular and non-uniform, so it was difficult to accurately obtain the ray trajectory. In order to obtain accurate ray trajectory, three ray tracing methods with fourth-order accuracy were proposed. Via comparing the results with the analytical solutions of helical rays, it is found that the maximum relative error of the fourth-order Runge-Kutta method is 1.610-8, Richardson extrapolation method is 1.210-8, and Adams method is 1.210-11. The Adams method is a high-precision and high-speed method for ray tracing. An arbitrary point interpolation method based on the polynomial fitting can obtain higher accuracy refractive index field than that computed by distance inverse ratio method. The method was applied to compute the distorted wavefront caused by the flow field around the optical window of a missile, and the calculation results were compared. It is found that Adams linear multi-step method starts with Runge-Kutta method, but Admas method does not neglect the calculation results of the previous step and will not lead to the accumulation of errors, so the results are closer to the real solution, while Richardson extrapolation method calculates the optical path difference significantly different from the other two algorithms.
2019, 48(5): 503006.
doi: 10.3788/IRLA201948.0503006
As an important part of traceability chain for micro-nano geometric quantity, the grid standard template is the basic guarantee for the development of nano-technology. In order to achieve the rapid tracking and calibration of the effective area in the micro-nano grid structure, a tracking structure was designed to quickly locate the effective measurement area and orthogonally scanning direction. In order to meet the calibration requirements of different accuracy and size range, the grid standard template with multi-dimension and multi-parameter structure was designed and integrated in the same substrate. The measurement result error was analyzed and evaluated by the metrological nano measuring machine (NMM), which could characterize the traceability of grid standard template. The experimental results show that the grid standard template has good uniformity, accuracy and stability, and it is verified that the developed grid standard template can be used as an ideal reference standard for nano geometry traceability system.
