The use of terrestrial laser scanning (TLS) point clouds for tunnel deformation measurement has elicited much interest. However, general methods of point-cloud processing in tunnels are still under investigation, given the high accuracy and efficiency requirements in this area. This study discusses a systematic method of analyzing tunnel deformation. Point clouds from different stations need to be registered rapidly and with high accuracy before point-cloud processing. An orientation method of TLS in tunnels that uses a positioning base made in the laboratory is proposed for fast point-cloud registration. The calibration methods of the positioning base are demonstrated herein. In addition, an improved moving least-squares method is proposed as a way to reconstruct the centerline of a tunnel from unorganized point clouds. Then, the normal planes of the centerline are calculated and are used to serve as the reference plane for point-cloud projection. The convergence of the tunnel cross-section is analyzed, based on each point cloud slice, to determine the safety status of the tunnel. Furthermore, the results of the deformation analysis of a particular shield tunnel site are briefly discussed.
Historic buildings combining functional, historic, scientific, art and social values, deserve scientific conservation. Thus, it is of significance to establish the information archiving. This paper mainly focuses on 3D reverse modeling and building information modeling of historic buildings, laying a foundation for digital archiving and life-cycle maintenance management. According to the conservation requirements and data characteristics for different parts of historic buildings, three-dimensional laser scanning, UAV aerial photography and close-range photography are selected to acquire point cloud model. And then, the 3D geometric model of a historical building can be created by 3DS Max and Geomagic, and integrated in 3DS Max. In order to solve the problem of poor generality and large amount of data of geometric model created by reverse modeling technology, an efficient way to transform geometric model to BIM is proposed. Components are automatically identified and classified according to their characteristics with Maxscript language, and the geometric information of components is imported into text files according to the syntax of component's creation in Revit API. Then, a program called Revit API was developed to read the text files and to fulfill data compression through parameter analysis of components in historical buildings, and the 3D geometrical model of the historical building was automatically transformed into a building information model, which can integrate many types of information such as history, structure and materials. Finally, taking Shanghai Jade Buddha Temple as an example to verify the validity of the above procedure. Its BIM model is successfully generated and has been developed into a 4D model by integrating the past repair and rehabilitation information.
As fundamental load-bearing parts, the cylindrical steel structures of transmission towers relate to the stability of the main structures in terms of topological relation and performance. Therefore, the periodic monitoring of a cylindrical steel structure is necessary to maintain the safety and stability of existing structures in energy transmission. Most studies on deformation analysis are still focused on the process of identifying discrepancies in the state of a structure by observing it at different times, yet relative deformation analysis based on the data acquired in single time has not been investigated effectively. In this study, the piecewise cylinder fitting method is presented to fit the point clouds collected at a single time to compute the relative inclination of a cylindrical steel structure. The standard deviation is adopted as a measure to evaluate the degree of structure deformation. Meanwhile, the inclination rate of each section is compared with the conventional method on the basis of the piecewise cylinder fitting parameters. The validity and accuracy of the algorithm are verified by real transmission tower point cloud data. Experimental results show that the piecewise cylinder fitting algorithm proposed in this research can meet the accuracy requirements of cylindrical steel structure deformation analysis and has high application value in the field of structure deformation monitoring.
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