Abstract
Abstract. With the improvement of the accuracy and efficiency of laser scanning technology, high-resolution terrestrial laser scanning (TLS) technology can obtain high precise points-cloud and density distribution and can be applied to high-precision deformation monitoring of subway tunnels and high-speed railway bridges and other fields. In this paper, a new approach using a points-cloud segmentation method based on vectors of neighbor points and surface fitting method based on moving least squares was proposed and applied to subway tunnel deformation monitoring in Tianjin combined with a new high-resolution terrestrial laser scanner (Riegl VZ-400). There were three main procedures. Firstly, a points-cloud consisted of several scanning was registered by linearized iterative least squares approach to improve the accuracy of registration, and several control points were acquired by total stations (TS) and then adjusted. Secondly, the registered points-cloud was resampled and segmented based on vectors of neighbor points to select suitable points. Thirdly, the selected points were used to fit the subway tunnel surface with moving least squares algorithm. Then a series of parallel sections obtained from temporal series of fitting tunnel surfaces were compared to analysis the deformation. Finally, the results of the approach in z direction were compared with the fiber optical displacement sensor approach and the results in x, y directions were compared with TS respectively, and comparison results showed the accuracy errors of x, y, z directions were respectively about 1.5 mm, 2 mm, 1 mm. Therefore the new approach using high-resolution TLS can meet the demand of subway tunnel deformation monitoring.
Highlights
With the development of laser scanning technique, its accuracy keeps enhancing
According to these researches some problems existed in the deformation monitoring of tunnels by using terrestrial laser scanning (TLS): firstly, because of lacks of some necessary control strategies, the registration accuracy of the point cloud data acquired in a few adjacent stations in the tunnel is a little low, so it needs to be improved; secondly, TLS can acquire magnanimity point cloud data causing that it is difficult to search out the homologous point in the scanning data acquired in different time, so there still is not a good approach to monitor dynamically just by using the original point cloud data
This paper analyzed the problems that existed in this application including low efficiency, low accuracy and hard to transform the coordinates as well as other problems, proposed a method of improving the accuracy of registration accuracy and solving the problem of the transformation of the coordinates by combining the TLS, the total stations (TS) and the level
Summary
With the development of laser scanning technique, its accuracy keeps enhancing. The single-point accuracy of phase laser scanner has reached 1mm, and which of the VZ-400 scanner from Riegl Company has reached 2mm. A deformation of a cylindrical tunnel was monitored by firstly fitting the cylindrical model and exploiting the statistical tests method to statistically analyze the deformation monitoring data of the tunnel (Van Gosliga et al, 2006) According to these researches some problems existed in the deformation monitoring of tunnels by using TLS: firstly, because of lacks of some necessary control strategies, the registration accuracy of the point cloud data acquired in a few adjacent stations in the tunnel is a little low, so it needs to be improved; secondly, TLS can acquire magnanimity point cloud data causing that it is difficult to search out the homologous point in the scanning data acquired in different time, so there still is not a good approach to monitor dynamically just by using the original point cloud data.
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