Research On Key Technology Of Tunnel Point Cloud Data Processing And Visualization

With the rapid development of the city,Metro tunnels are playing an increasingly important role in urban transport,and Real-time safety monitoring of subway tunnels is an important link to ensure its safe and efficient operation.The traditional means of monitoring can't reflect the overall deformation of the tunnel,meanwhile the monitoring efficiency is low and the cost is high.Three-dimensional laser scanning technology has broken through the traditional single-point measurement method with high precision,high efficiency,non-contact,real-time dynamic and other unique advantages,which provides a new means for solving the tunnel monitoring.Therefore,this paper focuses on the three aspects of tunnel point cloud data acquisition,tunnel point cloud processing and tunnel point cloud analysis,several key technologies of 3D laser scanning technology for tunnel monitoring are studied.1)Firstly,the principle of 3D laser scanning technology is expounded,the method of determining the scanning pitch and the resolution of the station aiming at the Error Source of 3D Laser Scanner in Tunnel Survey is discussed.According to the existing target layout and splicing scheme,an optimization scheme based on the rear view splicing of the scanner is designed to improve the measurement efficiency while avoiding the error transmission of multi-station splicing;an improved ICP algorithm is studied,and the iterative nearest point algorithm is applied to the fine splicing of the site cloud,not only solving the scanner backstroke stitching brought the error,but also meeting the tunnel deformation monitoring of the splicing accuracy.Experiments show that the method can achieve the effect of millimeter mosaic.2)In the aspect of cloud data processing,the tunnel point cloud filtering based on RANSAC algorithm and the point cloud compression based on Octree principle are realized,combined with the actual point cloud data of Shanghai subway tunnel,the best filtering and compression streamline parameters are given;method of intercepting continuous section of tunnel in space is studied,the accuracy of the extraction of the axis in the space is verified by the cross prong of the tunnel;the intercepted point cloud is obtained by coordinate transformation and coordinate projection to obtain two-dimensional coordinates of the point cloud,the fitting precision of the fitting method of five function approximations is discussed,method of Fourier function approximation is used to segment the point cloud to get the final section line,this method ensures the details of the tunnel deformation,meanwhile it is more conducive to the deformation of the tunnel analysis.3)Three-dimensional reconstruction and visualization of the tunnel are realized and the reconstruction accuracy is verified.The deformation analysis method based on section line and tunnel model is studied,the former can achieve a single section of the specific deformation of the situation,the latter can get the overall settlement of the tunnel.The model of the excavated tunnel is established and the overburden excavation condition is analyzed.The method of grid division is used to calculate the amount of overburden excavation.