| In recent years, with the constant innovation of surveying and mapping technology, the way of information acquisition of measured object in the surveying is also changing: from contact survey to non-contact survey, from single-point survey to the comprehensive information collection of measured object surface. Three-dimensional laser scanner as the product incorporating those changes with the characteristics of high efficiency, high-precision, large amount of data, digital data acquisition breaks through the shortcomings of the traditional measure methods and becomes one of the main methods of mass data acquisition. With the continuous improvement of the three-dimensional laser scanner technology, the data quantity is more and more big, the accuracy of point cloud data acquisition by three-dimensional laser scanner is more and more high, and it will be put in application in some field. In metro shield tunnel deformation monitoring, we can use on-board three-dimensional laser scanner to scan quickly the whole tunnel profile, and get complete mass data information about the metro shield tunnel, then we can also analysis deformation of the tunnel by processing the data. It has an important application value to research mass point cloud data of metro shield tunnel by three-dimensional laser scanner in tunnel deformation monitoring. This article mainly researches on mass point cloud data processing and application of laser scanning in metro shield tunnel. The main finished work is as follows:1. The research background and the significance of deformation monitoring of metro shield tunnel are elaborated in this paper. The disadvantage and problems of the traditional deformation monitoring methods are analyzed. The research situation and prospect of metro shield tunnel deformation monitoring technology is discussed.2. The method of mass point cloud data acquisition by the three-dimensional laser scanner is discussed. The way to work and the workflow of on-board three-dimensional laser scanner is summarized. The characteristics of three-dimensional laser scanner and mass point cloud data is analyzed. The application and the research status of mass point cloud data are discussed at home and abroad.3. To deformation monitoring of metro shield tunnel, the paper main researches tunnel section data extraction from mass point cloud, data post-preprocessing, the tunnel section curve fitting and so on. Because the trajectory is spiral in the surveying by the on-board three-dimensional laser scanner, we need to extract a certain bandwidth section on the mileage location to ensure to get enough data to reflect the situation of this section. The noise points data processing is divided into two steps, at first, rectangular coordinate method is used to eliminate the lager error noise points; then RANSAC algorithm is used to process accurately the data again to ensure that the noise points have little influence on the subsequent curve fitting. For tunnel section curve fitting, this paper proposes a new method based on least squares:the RANSAC-LSM method. The algorithm of RANSAC-LSM improves the accuracy and reliability of the curve fitting and effectively solves these problems that the algorithm of RANSAC is affected by the number of iterations and the least squares method is affected by the larger error data at the same time.4. This paper mainly analyses three aspects of tunnel deformation:tunnel section deformation, segment dislocation, convergence. I develop a program based on the above algorithms that can that can output result of section deformation, segment dislocation, convergence. We can use the result to analysis the deformation of the tunnel.5. These algorithms and the program are verified by three-dimensional scanned data of Beijing metro airport express, Nanjing metro Line 2 and Ningbo metro Line 2. It is proven that the accuracy requirement of point cloud curve fitting method can be satisfied by proposed in this paper. |
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