Abstract Maintenance of the rail track plays an important role in the policies that promote railway transport in the European Union. Each member state has its own railway infrastructure manager that is regulated by the standards set by the European Committee for Standardization (CEN). The standards define three levels for the track geometric quality: the alert limit (AL), the intervention limit (IL), and the immediate action limit (IAL). In the United States, the Federal Railroad Administration (FRA) manages the railroad safety and national rail transportation policy. They classify nine classes of tracks depending on the maximum allowable speed for freight and passenger trains; each classification has its own track geometric limits from nominal values. Usually, track-survey cars are used to measure the parameters of the geometric quality of the tracks in long sectors, whereas traditional surveying methods (TSMs) or an automated measuring system based on a track-surveying trolley assisted by a robotic total...

Abstract The performance of navigation sensors may be seriously affected by the operating rotors of a drone. To address this kind of disturbance, a low-cost multisensor integrated navigation system was developed for a quadrotor aerial vehicle (QAV). The navigation board integrates a global positioning system (GPS) module, triaxial gyroscope, accelerometer, magnetometer, and a digital barometer. The sensors’ outputs were mathematically modeled and subsequently used in the integration Kalman filter. The data processing consisted of several steps: prefiltering, centralized filtering, and feedback. On the basis of onboard tests, the stochastic models of sensors were established in the presence of vibration, revolution, and ventilation caused by the QAV rotor’s operation, and in particular, its electromagnetic and aerodynamic characteristics. Flight experiments indicate that the proposed integrated navigation system can significantly improve flight accuracy and reliability.

The detection of multiple outliers can be interpreted as a model selection problem. Models that can be selected are the null model, which indicates an outlier free set of observations, or a class of alternative models, which contain a set of additional bias parameters. A common way to select the right model is by using a statistical hypothesis test. In geodesy data snooping is most popular. Another approach arises from information theory. Here, the Akaike information criterion (AIC) is used to select an appropriate model for a given set of observations. The AIC is based on the Kullback-Leibler divergence, which describes the discrepancy between the model candidates. Both approaches are discussed and applied to test problems: the fitting of a straight line and a geodetic network. Some relationships between data snooping and information criteria are discussed. When compared, it turns out that the information criteria approach is more simple and elegant. Along with AIC there are many alternative information criteria for selecting different outliers, and it is not clear which one is optimal.

Abstract This paper offers a new method for mapping as-built tunnels excavated by tunnel-boring machines (TBMs) that is conveniently applicable and cost-effective. The presented procedure can algorithmically be explained as follows: (1) surveying some points on the edge of each segment using a reflectorless total station in an arbitrarily initial coordinate system, (2) shifting the measured coordinates to a location as close as the origin of the initial frame, (3) fitting a plane to the shifted coordinates of the measuring points, (4) deriving the direction angles between the normal vector and the axes of the coordinate system, (5) rotating the shifted coordinates around the third and first axes of the frame, (6) fitting a circle to the transformed coordinates to determine the position of its origin, and (7) transforming the derived coordinates of the circle origin into the initial coordinate system. The capability and reliability of the method have been indicated by means of simulated data sets. The metho...

The calibration and accuracy analysis of a novel, low-cost, adaptable mobile laser scanning (MLS) system using a Velodyne HDL-32E laser scanner and an Oxford Technical Solutions Inertial+2 inertial navigation system, is described. First, a static calibration of the laser scanner is discussed. The static calibration is shown to improve the overall relative accuracy of point cloud data from the scanner by approximately 20% over the manufacturer-supplied calibration. Then, the determination of system boresight angles and lever-arm offsets using a planar patch least-squares approach is presented. Finally, the calibrated and boresighted MLS is operated in a backpack mode to acquire multiple data sets in an area that contains dense ground control acquired using static terrestrial laser scanning (TLS) and a high-end, survey-grade MLS. The dense ground control is used to examine several methods of estimating the overall errors of the backpack MLS system. Detailed comparison of the MLS data with the TLS and survey-grade MLS control shows that, despite the system’s low cost, it is able to reliably collect point cloud data with greater than 10-cm three-dimensional root-mean-square error accuracy.

Abstract A novel approach to a three-dimensional (3D) model creation from data sets obtained by laser scanning or photogrammetry is presented, including a description of the method and efficient numerical algorithms for 3D model creation for surveying applications. The presented method solves the fundamental problem of surface reconstruction by constructing models using differential geometry and partial differential equations. The time-relaxed eikonal equation was used to obtain the distance function from the cloud of points, and the 3D model was then created by the evolution of an initial guess by the advection equation regularized by curvature, where the advective velocity is given by the gradient of the computed distance function. The partial differential equations were discretized by the finite-difference schemes, and the results of the 3D model creation are presented and discussed.

Abstract This paper presents a closed-form procedure for the coarse registration of three-dimensional (3D) point clouds using automatically extracted linear features, which have been manually matched. Corresponding linear features are defined by nonconjugate endpoints that do not necessarily define compatible direction vectors. Because the point clouds could be derived from different sources (e.g., laser scanning data sets and/or photogrammetric point clouds that are referenced to arbitrary reference frames), the proposed procedure estimates the scale, shift, and rotation parameters that relate the reference frames of these data sets. The proposed approach starts with a quaternion-based procedure for initial estimation of the transformation parameters using the minimal number of required conjugate line pairs (i.e., two noncoplanar linear features from each point cloud). The initial estimate of the transformation parameters is then used to ensure the compatibility of the direction vectors of the involved li...

Abstract The use of terrain and elevation data is critical for a number of applications in science and engineering. Typically, the quality of digital elevation models (DEMs) is assessed using external and independent point data sources to arrive at an overall RMS value for the errors. The utility of such a single-valued overall assessment depends on the spatial extent of the area under consideration and the terrain variability (both over time and space), as well as the application requirements. This paper aimed to understand the suite of parameters that are important to consider in deriving a DEM error budget. Specifically, terrain slope, land-cover type, information loss, and data measurement schemes were investigated. A region in western Canada spanning the Rocky Mountains was used to numerically quantify errors using two Global Positioning System (GPS) datasets: precise point positioning (PPP) profiles and GPS on benchmarks. Three digital elevation models [Advanced Spaceborne Thermal Emission and Reflec...

The moon is the brightest celestial body in the night sky, and it is of some value when determining the astronomical azimuth on a cloudy or foggy night or in a light-polluted city when there is no visible star. Based on the edge observations of the apparent moon using a total station, a global positioning system (GPS) receiver, a portable computer, and some appropriate software and instrumentation, an innovative method for determining the center of the apparent moon, is discussed in this paper, and calculation formulas are deduced in detail. Second, errors in the astronomical azimuth determination are quantitatively analyzed. Finally, two practical tests are performed in the central plains of China, and the results indicate that the difference between azimuth determination by Polaris and the moon is up to 7″ from two field tests.

The authors investigated the possibility of expanding the application of global navigation satellite systems (GNSS) into the monitoring of stiff civil-engineering structures from the current limit of dominant frequencies of 3–4 Hz to a new limit of 6–7 Hz. On the basis of experience from previous supervised learning experiments, the authors analyzed 100-Hz GNSS data collected with an optimal phase-locked loop and collocated accelerometer data, both describing the attenuation of forced excitations of a timber pedestrian bridge. Computed vertical apparent deflections were masked by noise, but it was still possible to accurately identify the natural frequency of the bridge, equal to 6.5 Hz, and weak fusion with accelerometer data led to accurate oscillation waveforms. The quality of the latter was assessed by structural constraints and by comparison of waveforms of acceleration and of damping ratios derived from GNSS and from accelerometers. These results made it possible to (1) assess the quality of 100-Hz data in monitoring real structures, (2) propose methods for deriving highly dynamic deflections on the order of a few millimeters, and (3) expand the application of GNSS into the measurement of three-dimensional dynamic deflections of stiffer structures, i.e., with natural frequencies of up to 6–7 Hz and vertical deflections of a few millimeters only—an important contribution to structural-health monitoring and structural identification.