Journal of Surveying Engineering

The paper focuses on a specific errors-in-variables (EIV) model named the linearly structured EIV (LSEIV) model in which all the random elements of design matrix are in a linear combination of an input vector with random errors. Two existing structured total least-squares (STLS) algorithms named constrained TLS (CTLS) and structured TLS normalization (STLN) are introduced to solve the LSEIV model by treating the input and output vectors as the noisy structure vectors. For comparison purposes, the weighted TLS (WTLS) method is also performed based on the partial EIV model. Approximated accuracy assessment methods are also presented. The plane fitting and Bursa transformation examples are illustrated to demonstrate the accuracy and computational efficiency performance of the proposed algorithms. It shows that the proposed STLS and WTLS algorithms can achieve the same accuracy if the dispersion matrix of the WTLS method is constructed based on the partial EIV model.

An important issue in deformation analysis is identification of (un)stable points in a monitoring network. This paper proposes a new method that identifies the unstable points of a network based on the generalized likelihood ratio (GLR) test. The method, which simultaneously uses the observations of two epochs, is called the simultaneous adjustment of two epochs (SATE) method. The existing methods apply individual least-squares adjustment to the observations of each epoch. SATE is applicable to one-, two-, or three-dimensional deformation networks with any type of observations, including distances, angles, global positioning system (GPS) baselines, and height difference. To investigate the performance of the proposed method, observations of a real GPS deformation-monitoring network were used. The results for unstable points identification are identical to those of the existing methods. Furthermore, a few simulation case studies were used to evaluate the efficacy of the proposed method. The simulated results for the deformation-monitoring networks, with different scenarios, confirm that the proposed method always performs the best. This method can thus be introduced as a reliable method that provides results that are superior to those of the two existing classical methods.

This paper presents a new framework of road feature extraction from color component–based data fusion of aerial imagery and lidar data. The proposed framework consists of six procedures: (1) removal of elevated objects (e.g., buildings) from lidar data with a flatness index constraint; (2) removal of shadows and vegetation from aerial images using the Otsu segmentation; (3) data fusion of the modified lidar data and aerial images; (4) initial extraction of road features from the fused data; (5) refinement of road features to remove false positives and join up misclosures; and (6) final extraction of road surfaces and centerlines. A new method is proposed for data fusion of aerial images and lidar data to extract road features by utilizing color components, such as luminance, saturation, and hue, in hue/saturation/intensity and brightness/blue difference/red difference color spaces. A series of refinement processes, including hierarchical median filtering and k-nearest-neighborhood, are implemented to remove open areas (e.g., parking lots) of the road extraction results. A local spatial interpolation method is applied to join up misclosures, and curve fitting is used to obtain accurate road centerlines. The results of tests on sample data sets indicate that the proposed framework performs well, with high accuracy, completeness, and quality.

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.

In 1997, the National Geodetic Survey (NGS) published static global positioning system (GPS) surveying guidelines for determining ellipsoidal heights on marks. These guidelines, commonly referred to as NGS-58, are used today in the United States for modernizing heights on marks. Later, in 2013, the NGS released OPUS-Projects, a web-based tool for processing GPS surveys. To evaluate OPUS-Projects and compare it with NGS-58, a static GPS survey was conducted in Oregon. The data were used to develop four different networks. For the most part, the recommendations in NGS-58 worked well, but the 1-h observations did not always produce accurate ellipsoidal heights for baselines longer than 7 km. For the other networks that consisted of 5-h observations or greater, the resulting ellipsoidal heights on all of the marks agreed within ± 1 cm. For these networks, the estimated network accuracy of the ellipsoidal height for each mark was less than 1.2 cm at 95% confidence. Such consistent results indicate that OPUS-Projects can be used for height modernization surveys.

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 station is chosen for short sectors. In this paper, the authors analyze the precision and performance obtained with the TSM and with an automatic measuring system in its different working modes (stop and go and kinematic), comparing the measured geometric values with the nominal values for a section of a track. The results indicate that TSM and stop-and-go modes yield similar precisions, so both methods can be used to detect the geometric quality levels defined in the CEN and FRA standards. In contrast, kinematic is less accurate, so there are situations where it cannot be used to determine the geometric quality levels. Finally, the authors discuss some recommendations to improve the performance and working methods with the track-surveying trolley.

Engineers use spatial information. Mapping and wayfinding in the real world are activities that use spatial orientation skills. A set of resources available on the Internet whereby engineers work with maps and spatial georeferenced information is termed geographic information science (GISc), which allows the use of mapping and exploratory navigation with maps and a continuous three-dimensional (3D) digital image of the real world to simulate navigation at a ground-level perspective. In this case study, a workshop composed of 193 civil engineering students, 35 belonging to a control group, was conducted to determine whether spatial orientation skills can be developed through map reading and the virtual wayfinding experience. After the workshop, the results showed a significant improvement in the spatial orientation skill, ranging between a minimum of 14.56° and a maximum of 26.61° rank in the Perspective Taking/Spatial Orientation Test: training had a positive impact on the development of spatial orientation skills. The control group results confirmed that students who were not subject to specific training did not increase their spatial orientation skill.

National vertical data are mostly referenced to a tidal level of one or more tidal stations. The Keelung tidal station has been serving as the reference tidal station of the Taiwan National Height Datum for more than one century; all orthometric height in Taiwan is zeroed to the mean sea level (MSL) of an astronomical period of this station. A monument of the Taiwan height origin was established nearby, but due to construction, the height origin was relocated to the newly built National Museum of Marine Science and Technology in Badouzi. This article documents the search for an improved definition of the tidal reference for height origin in Taiwan. The selection criteria identified include geological stability; sufficient depth of water; limited influence from nontidal effects, such as passing vessels; and proximity to the monument of height origin. As part of the preliminary assessment, a tidal station was established at the nearby Cheng-Bin fishery port. The authors performed tidal comparisons of observations collected from the Keelung, Cheng-Bin, and nearby Longdong (to the east) and Taipei Harbor (to the west) stations. In addition to the harmonic analysis, tidal levels of different definitions were computed to determine the potential influence resulting from the change of reference tidal station to the national height datum. From concurrent observations over 3 months, from September 5 to December 17, 2013, the amplitude and phase of significant tidal components were found to be similar between the Keelung and Cheng-Bin stations, whereas the Longdong and Taipei Harbor stations presented larger deviations. The differences between MSL calculations were significant. Although the deviation between the national vertical datum zero and the tidal level was noted in previous studies, the Cheng-Bin station showed relatively smaller changes. Although defining height system with geoid and sea surface topography preserves a more physical and geometric definition of height, a MSL-based definition with a group of coordinated tidal stations may serve as a more reliable scheme for the transitional period.

Deformation measurements are repeatable. Therefore, they are often performed with the same equipment, methods, and geometric conditions in different epochs. However, although the measuring environment might be the same in different epochs, it sometimes changes significantly. Of all environmental parameters (atmospheric pressure, temperature, etc.), the atmospheric refraction coefficient is the most significant. Because it is unstable and changeable, measurement accuracy is affected. To solve this issue, an inversion method of the atmospheric refraction coefficient based on a trigonometric leveling network is proposed. This method is based on a mathematical model of the atmospheric refraction coefficient with weighted values, which are determined according to the difference between direct and reversed elevations. Therefore, the weighted average height of the closure errors of all triangles are considered. By iterative calculation, the atmospheric refraction coefficient is estimated. The estimated atmospheric refraction coefficient is applied successfully to the adjustment and analysis of the external control network of a dam. In this aspect, one does not need to solve the atmospheric refraction coefficient for each station and edge. Moreover, one of the most suitable atmospheric refraction coefficients for the whole trigonometric leveling network can be provided from the relevant conditions. The approach provides the advantages of flexibility and practicality, effectively weakening the influence of the atmospheric refraction coefficient on measurement accuracy in the trigonometric leveling network. Furthermore, it provides a theoretical basis for further engineering applications.

The purpose of this research was to fit a high-accuracy levelling network to points of the vertical national control network, the control points of which are unstable because of vertical terrain movements caused by underground mining. For this reason, the robust M-estimation is used to reduce a negative impact of control points with gross errors on the estimated parameters. Because it has been found that the classical nonlinear Huber mean error function does not lead to any reasonable solutions, a new error function, a linear modification of Huber’s function, is introduced here. Using this function, a consistent solution of the robust adjustment and correct values of the estimated parameters can be achieved. To validate the results, other robust weight functions proposed by other authors are implemented as well. The results obtained in the particular variants are very close to those obtained using the proposed linear modification of Huber’s function. Moreover, the authors propose an adjustment strategy that is based on the combination of classical and robust adjustment, which can be applied to identify unstable control points in a levelling network.