Abstract
The large number of bolts and screws that attached to the subway shield ring plates, along with the great amount of accessories of metal stents and electrical equipments mounted on the tunnel walls, make the laser point cloud data include lots of non-tunnel section points (hereinafter referred to as non-points), therefore affecting the accuracy for modeling and deformation monitoring. This paper proposed a filtering method for the point cloud based on the elliptic cylindrical model. The original laser point cloud data was firstly projected onto a horizontal plane, and a searching algorithm was given to extract the edging points of both sides, which were used further to fit the tunnel central axis. Along the axis the point cloud was segmented regionally, and then fitted as smooth elliptic cylindrical surface by means of iteration. This processing enabled the automatic filtering of those inner wall non-points. Experiments of two groups showed coincident results, that the elliptic cylindrical model based method could effectively filter out the non-points, and meet the accuracy requirements for subway deformation monitoring. The method provides a new mode for the periodic monitoring of tunnel sections all-around deformation in subways routine operation and maintenance.
Highlights
With the rapid development of 3D laser scanning technology and the improvement of measurement accuracy, the application of laser scanning technology has been extended to the field of precision engineering measurement (Waldemar Kociuba et al, 2015;Cheng-Wei Kuo et al, 2015;Anne Griebel et al, 2015). 3D laser scanning technology can expanded the monitoring method from discrete points to comprehensive surface in the deformation monitoring of subway tunnel’s daily operation and maintenance, which provides a new and efficient methods for routine monitoring method
Extraction the edge of tunnel points according to the rule of searching used for fitting the tunnel axis after putting the original point cloud of tunnel projection to the horizontal surface; divided the point cloud data into equal intervals along the axis, and using elliptic cylinder model proposed by this paper for each area of point cloud data to filter non-points of the tunnel
The point cloud after region segmentation can be regarded as elliptical cylinder and its direction is parallel to X axis, so the discrete point set can be fitted to the elliptic curve by using the Y and Z coordinates: ( y y0 )2 a2
Summary
With the rapid development of 3D laser scanning technology and the improvement of measurement accuracy, the application of laser scanning technology has been extended to the field of precision engineering measurement (Waldemar Kociuba et al, 2015;Cheng-Wei Kuo et al, 2015;Anne Griebel et al, 2015). 3D laser scanning technology can expanded the monitoring method from discrete points to comprehensive surface in the deformation monitoring of subway tunnel’s daily operation and maintenance, which provides a new and efficient methods for routine monitoring method. 2014), combine intensity textures and local geometry(Luca Penasa et al, 2014), shape-based segmentation method(Bisheng Yang and Zhen Dong, 2013) and so on; The filtering(classification) algorithm. Different filtering algorithms are proposed for different sources of laser scanning and obtained good results. It is not work for the special structure of the subway tunnel. Construct tunnel DSM and take overlay analysis based on surface deformation monitoring method
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