基于地面三维激光扫描技术的隧道全断面变形测量方法

采用地面三维激光扫描技术测量隧道全断面变形,解决数据采集和数据处理两大方面的问题。数据采集方面,为兼顾数据采集的精度与效率,通过几何分析方法对关键的扫描参数进行优化,给出测站间距和扫描分辨率的最佳取值。讨论隧道内多个测站数据的拼接方法以及不同标靶布设方式对拼接精度的影响,建议采用全局拼接方案以减少误差。数据处理方面,由于地面三维激光扫描的原始数据(称为“点云”)不能直观地表示隧道的变形,因此提出基于点云的隧道三维建模算法,使隧道变形可视化。该算法联合采用圆柱面拟合与椭圆拟合进行点云建模,并运用误差分布统计规律进行点云降噪。通过与全站仪的精度比较试验,验证地面三维激光扫描技术在隧道变形测量中的可靠性,利用隧道三维建模算法得到的变形量与全站仪的测量结果相差在2 mm以内。最后,介绍上海西藏路电力隧道以及上海长江西路越江隧道2个工程案例,第一个案例给出单空间隧道中的数据采集和数据处理的全过程及隧道变形结果,第二个案例介绍多空间隧道中的测站及标靶的布设方法。     

Deviation analysis method for the assessment of the quality of the as-is Building Information Models generated from point cloud data

Generating three-dimensional (3D) as-is Building Information Models (BIMs), representative of the existing conditions of buildings, from point cloud data collected by laser scanners is becoming common practice. However, generation of such models currently is mostly performed manually, and errors can be introduced during data collection, pre-processing, and modeling. This paper presents a method for assessing the quality of as-is BIMs generated from point cloud data by analyzing the patterns of geometric deviations between the model and the point cloud data. The fundamental assumption is that the point cloud and the as-is BIM generated from the point cloud should corroborate in the depiction of the components and their spatial attributes. Major geometric deviations between as-is models and point clouds can indicate potential errors introduced during data collection, processing and/or model generation. The research described in this paper provides a taxonomy for patterns of deviations and sources of errors and demonstrates that it is possible to identify the source, magnitude, and nature of errors by analyzing the deviation patterns. The method is validated through a comparison with the currently adopted physical measurement method in a case study. The results show that the deviation analysis method is capable of identifying almost six times more errors with more than 40% time savings compared to the physical measurement method.     

Design and optimisation of laser scanning for tunnels geometry inspection

The use of terrestrial laser scanning technology in engineering surveys is gaining an increasing interest due to the very high spatial density of the acquired data. Recent improvements regarding the speed, accuracy, software algorithms and the fall in price have introduced a high potential for large scale applications of this technology in highly demanding engineering environments such as tunnels. Railway tunnels, in particular those of a long length, create challenges for surveyors due to their elongation to obtain satisfactory geometry of the scanned data. The purpose of this paper is to give an optimal solution for surveying tunnel geometry using laser scanning technology to reliably inspect railway tunnels and create “as-built” documentation.The proposed methodology provides optimisation of scanning parameters, scans registration, the georeferencing approach and the survey control network design. The maximal size of the scanner shifting along the tunnel alignment is primarily conditioned by factors including the incidence angle of the laser beam and the point density distribution. The authors introduce the so-called arbitrary georeferencing approach in long tunnel scanning that controls the point cloud geometric distortions to the required limits and contributes to time and material resources savings. Optimal design of the survey control network ensures the required positional accuracy and the reliability of the measurements, together with a cost effective approach to tunnels surveying.The proposed methodology is followed by the empirical results of the modelling and profiling of 12 tunnels in a single track railway. The lengths of these tunnels are from 60 m to 1260 m, with a total length of 3.5 km. Due to the specific geometry of the case study tunnels, the maximal favourable laser incidence angle is 78° with a distance of 13 m and consequently the optimal size of the scanner shifting along the tunnel alignment is 26 m. The survey control network is designed with the condition that the optimal reliability factors are within the required limits for engineering networks. A priori estimation of the control network positional uncertainty and a posteriori adjustment results shows that the achieved positional accuracy of the control points is approximately five times better than the requested absolute accuracy of the tunnel model: σ_m = 2 cm. On the largest tunnel example it is shown that the arbitrary georeferencing approach assures that the optimal registration error size is within the requested limits.     

Automating surface flatness control using terrestrial laser scanning and building information models

Current practice in the control of surface flatness requires a significant amount of time and labor, and delivers results based on few sample measurements. Developments of Terrestrial Laser Scanning (TLS) and Building Information Modeling (BIM) offer great opportunities to achieve a leap forward in the efficiency and completeness of dimensional control operations. This paper presents an approach that demonstrates the value of this integration for surface flatness control. The approach employs the Scan-vs-BIM principle of Bosché and Haas (2008) to segment TLS point clouds acquired on-site, by matching each point to the corresponding object in the BIM model. The novel approach then automatically applies two different standard flatness control techniques, Straightedge and F-Numbers, to the TLS points associated to each floor, and concludes with regard to their compliance with given tolerances. The approach is tested and validated using data from two actual concrete slabs. Results confirm the suitability of using TLS for conducting standard dimensional controls, and validate the performance of our system when compared to traditional measurement methods (in terms of both quality and efficiency). Furthermore, a novel straightedge generation method is proposed and demonstrated that enables more complete and homogeneous analysis of floor flatness for insignificant additional processing times.     

超高层建筑工程变形监测中小角度钢尺测边交会点的精度改良

通过规范中的测边交会点的坐标计算公式,按误差传播规律,分析出交会点的误差计算公式.在此基础上,通过理论分析,改良小角度三角形图形强度,找出测边交会小角度三角形的最高精度的交会点,分析坐标值及其点位最高精度值.研究结果表明,改良后交会点位精度值除与最佳图形--等边三角形的交会精度很接近外,还提高了变形监测点的精度等级.同时为变形监测、控制测量、施工放样测量等工作中出现小角度三角形,为优化测量点位误差提供了一种解决问题的新途径.     

稳健整体最小二乘直线拟合

针对常用直线拟合方法在数据存在粗差或异常值扰动时,存在拟合结果不稳定的缺点,提出一种稳健的直线拟合方法。该法以整体最小二乘法为基础,在考虑全部观测量存在误差的情况下,通过利用一定的准则删除数据中的粗差或异常值,从而获得稳健的直线参数。实验结果表明,稳健整体最小二乘直线拟合不仅考虑了全部观测值中的误差,而且能剔除数据中的粗差或异常值,精度更高,结果更为可靠。     

Gage‐Free Stress Estimation of a Beam‐like Structure Based on Terrestrial Laser Scanning

Abstract: Terrestrial laser scanning (TLS) is a technique that remotely obtains the three‐dimensional (3D) coordinates of an object using laser pulses. It is advantageous when used to obtain the 3D coordinates of the overall shape as well as any particular area or point of a target object. In addition, using TLS for the stress monitoring of structures will not require the installation of a sensor on the target structure whose structural response will be assessed. Thus, TLS can resolve the limitations of conventional sensors based on strain monitoring. This article presents a computational model for the automatic estimation of the stresses of beam structures using TLS in association with a finite element method. The method is experimentally applied to the stress estimation of a simply supported steel beam subjected to a concentrated load. In this experimentation, the maximum and minimum errors between the estimated stresses using TLS and directly measured stresses from electrical strain gages are found to be 7.2% and 2.2%, respectively.     

基坑开挖引起邻近盾构隧道转动与错台变形计算

基坑开挖会对邻近盾构隧道的变形产生显著影响。考虑基坑开挖时卸载在隧道轴线处产生的附加应力,建立了综合考虑剪切错台变形和刚体转动变形的隧道变形计算模型,结合最小势能原理推导出隧道的纵向变形量、环间错台量、环间转角和环间剪切力的计算公式。选取两组工程实例进行分析,将计算结果与实测数据进行比较。研究结果表明:邻近并平行于盾构隧道的基坑侧壁的卸荷效应对旁边隧道的影响最大;隧道水平位移最大值附近的管片基本不发生错台变形和刚体转动变形,环间剪切力值也很小;而在隧道水平位移曲线的反弯点处,隧道的剪切错台量、环间转角和环间剪切力值达到最大;在基坑开挖工况下,邻近隧道的水平位移变形模式以剪切错台为主,刚体转动为辅。     

基于三维激光扫描技术的病害隧道监测

现有病害隧道测量方法,存在费时、费力、精度低和连续性差等问题,利用三维激光扫描技术可有效解决这些弊端。于2009年和2010年利用三维激光扫描技术进行了2次现场扫描,通过点云数据预处理和拼接等步骤获得了华蓥山隧道的点云模型。随后利用点云模型,进行了路面破损测量和隧道变形监测。测量结果显示,2010年较2009年,路面裂缝地表最大宽度增大0.009 m,到达0.045 m,裂缝发育长度和密度有所降低;隧道净高增加0.030 9 m～0.322 7 m,平均为0.179 5 m,隧道净宽增加0.021 8 m～0.058 6 m,平均为0.039 5 m。     

Geostructural stability assessment of cave using rock surface discontinuity extracted from terrestrial laser scanning point cloud

The use of terrestrial laser scanning(TLS) in the caves has been growing drastically over the last decade.However, TLS application to cave stability assessment has not received much attention of researchers.This study attempted to utilize rock surface orientations obtained from TLS point cloud collected along cave passages to(1) investigate the influence of rock geostructure on cave passage development, and(2)assess cave stability by determining areas susceptible to different failure types. The TLS point cloud was divided into six parts(Entry hall, Chamber, Main hall, Shaft 1, Shaft 2 and Shaft 3), each representing different segments of the cave passages. Furthermore, the surface orientation information was extracted and grouped into surface discontinuity joint sets. The computed global mean and best-fit planes of the entire cave show that the outcrop dips 290° with a major north-south strike. But at individual level, the passages with dip angle between 26° and 80° are featured with dip direction of 75°-322°. Kinematic tests reveal the potential for various failure modes of rock slope. Our findings show that toppling is the dominant failure type accounting for high-risk rockfall in the cave, with probabilities of 75.26%, 43.07%and 24.82% in the Entry hall, Main hall and Shaft 2, respectively. Unlike Shaft 2 characterized by high risk of the three failure types(32.49%, 24.82% and 50%), the chamber and Shaft 3 passages are not suffering from slope failure. The results also show that the characteristics of rock geostructure considerably influence the development of the cave passages, and four sections of the cave are susceptible to different slope failure types, at varying degrees of risk.     

利用总体最小二乘估计AR模型参数及其在变形监测中的应用

本文在简单介绍ARMA（p,q）模型识别方法的基础上,推导了ARMA（p,q）模型向AR（p1）模型转换的方法。然后介绍了最小二乘法（LS）在AR模型参数估计中的应用,并指出了该方法的缺陷：在进行参数的估计时,只考虑了当期观测值的误差而并没有顾及系数矩阵的误差。在此基础上,将整体最小二乘（TLS）法引入到AR模型的参数求解中,详细介绍了TLS的解算方法。最后通过对具体工程实例的变形监测数据的分析,验证了采用了TLS法对AR模型参数估计及预报的可行性,并且比LS法具有更高的精度。     

乘性误差模型平差理论研究进展概述

传统的测量平差理论是在加性误差模型基础上发展起来,其测量误差的统计特性与模型待估参数无关。然而,现代对地观测技术已经清楚表明,测量随机误差由独立于测量值的加性误差和与之观测值真值成比例的乘性误差两部分组成。理论上,传统的大地测量平差理论与方法已不能满足现代对地观测中处理乘性或者加乘性混合随机误差的需要。本文概述了国内外乘性随机误差模型的理论与应用研究成果,总结了该模型的参数估计,单位权中误差估计及其精度评定方法,并对今后的研究简列浅见。     

基于TerraScan软件的点云数据滤波处理研究

点云滤波是地面三维激光扫描数据处理的重点和热点问题,也是点云数据处理的一项关键工作。本文在阐述目前几种主要的点云滤波方法的基础上,着重探讨了基于TerraScan软件的点云数据处理方法,如误差点剔除、点云分类、模型重建等。经实验数据分析取得了良好的滤波效果,能有效滤除点云噪声,同时很好地保持了地形特征。     

地铁隧道加测陀螺边最佳位置估算方案

受地铁隧道特定环境的限制,地下控制测量一般采用导线测量方式,其横向贯通误差最难控制。为了确保贯通测量的质量,可以适当加测陀螺方位,而加测陀螺方位的最佳位置就涉及设计问题。利用严密函数式可以计算导线端点的点位误差以及计算加测若干条陀螺方位的导线终点误差,进而推导出陀螺方位的最佳位置,但这种方法比较复杂,计算工作量大、且十分繁琐。利用以计算机仿真计算为主的现代控制网优化设计可以快速、有效解决上述问题。     

装配式建筑点云模型几何特征自动化提取方法研究

针对传统检测方法无法满足装配式建筑质量精度检验要求的问题,本文提出了一种基于点云模型的装配式建筑预制构件几何尺寸自动化提取方法。首先利用建筑结构空间位置关系及几何特点将典型预制构件点云从整体建筑点云中分割;对构件点云进行特征提取实现尺寸信息的测量;通过求取拟合平面法向量与垂直方向单位向量的夹角检测墙体的垂直度;利用点云切片提取柱中轴线来检测柱体的垂直度;再通过各点到拟合平面的中误差来表示板面平整度。研究以某装配式建筑施工现场采集的点云数据为例,对预制构件点云数据进行离群点剔除与切分,实现点云数据特征自动化提取和测量,测量精度均在95%以上,验证了方法的可行性和有效性。为实现典型预制构件的自动分割、尺寸测量以及参数化管理提供基础。     

安装误差对锥齿轮副性能的影响

锥齿轮副的安装误差包括轴交角误差、轴交错误差、轴交点误差和分锥顶点的位置误差等。这些误差将使齿轮副出现一端接触、压力角和旋转角发变化等现象。本文讨论了锥齿轮各种安装误产生的原因及其对性能的影响。     

基于激光扫描的隧道超欠挖量检测方法

隧道超欠挖检测是爆破成型质量评估的重要内容,对保障施工安全极为重要.针对施工过程的爆破隧道截面特点,提出了基于激光扫描的隧道超欠挖量检测方法.以二维激光扫描仪和车载云台为主搭建三维扫描装置,利用该装置通过多点设站采集整个隧道的三维点云数据并将其转换到同一大地坐标系下,计算隧道中轴线并提取隧道截面,检测隧道截面的超挖区域...     

电缆隧道切片点云的自动提取及几何参数分析

针对基准面与隧道内壁点云法向量及地面的关系,提出了自动提取隧道内壁切片点云数据算法。该算法利用三维激光扫描的隧道内壁点云数据进行法向量的解算,根据正交整体最小二乘进行隧道地面的拟合,利用基准面与地平面垂直及基准面与内壁点云法向量平行的关系进行最佳基准面的搜索,通过搜索到的基准面进行切片点云的提取。通过该算法可以在无标靶情况下自动获取切片点云。通过切片可以计算隧道内部的重心、重心距及重心到顶面的距离等几何参数,利用计算的几何参数可以随时监视隧道内壁的变化状况。对不同时期的隧道切片进行对比分析便可实现不同地段隧道的变形情况。     

Quantification of edge loss of laser scanned data at spatial discontinuities

Laser scanning is a promising geometric data collection tool for construction, facility, and infrastructure management due to its fast sampling rate (tens of thousands of measurements per second) and millimeter-level accuracy. However, laser scanned data contains inaccurate data points at spatial discontinuities (object edges). These inaccurate points, known as mixed-pixels, are commonly removed from the data prior to geometric modeling or other downstream processes. The removal of points at the edges of objects introduces error in the geometry of the objects, and object dimensions extracted from the data, such as widths and heights, are usually smaller than the actual values. In many cases, these losses due to removal of points at edges can exceed measurement accuracy tolerances specified in inspection manuals. This paper proposes a model for estimating edge loss in laser scanned data by considering the impacts of various factors, such as scanning distance, density of data and incidence angle on the edge loss. Results from a series of controlled experiments showed that the developed model successfully predicted edge losses in most test cases. Evaluation results using data collected from job sites showed that this model reduced the measurement error due to edge loss by an average of 80% for dense point clouds collected by an amplitude modulated continuous wave (AMCW) scanner, and 38% for relatively sparse point clouds collected by a pulsed time of flight (PTOF) scanner. By adding the estimated edge losses back into the raw dimensional measurements using the developed model, it is possible to significantly improve the accuracy of related measurements and hence improve the accuracy of the geometric information extracted from laser scanned data.     

测有多个陀螺方位角地下导线的平差及横向端点误差分析

盾构法施工的要点是需要在井下布设高精度的控制支导线 ,当遇超长盾构隧道施工时 ,采用传统的方法不能满足精度要求时 ,我们常常会考虑采用加测陀螺方位角的办法来控制导线端点的横向中误差。本文结合上海地铁某超长隧道探讨加测多个陀螺方位角的导线平差及端点的横向中误差的大小。