Journal of Surveying Engineering

To obtain more accurate formulas for precision estimation and to continue work on the adjustment of total least squares (TLS), the second-order approximation function method for the precision estimation of the TLS adjustment was investigated. According to least-squares (LS) criterion, the second-order Taylor expansions between parameter estimates or corrections and observational errors were derived. By the error propagation law, the formulas for biases in parameter estimates and residuals and the second-order approximate covariance and mean squared error matrices for the parameter estimates were obtained. Then, the implementation process of the second-order approximation function method for precision estimation was also designed. Results of the examples showed that the second-order approximation function method could effectively calculate biases and covariance or mean squared error matrices for precision estimation. The second-order approximation function method can provide more precision information for judging the qualities of parameter estimates and the nonlinear degree of the function model, contributing, in part, to the integrity of the theory on precision estimation of the TLS adjustment.

Although laser-scanning total propagated uncertainty (TPU) is an active topic in the research community, there is a current dearth of commercial or open-source software for generating point clouds with per-point, three-dimensional (3D) coordinate uncertainties from terrestrial, mobile, and airborne laser scanning. Consequentially, there is a corresponding lack of tools for on-the-fly 3D visualization of these point cloud uncertainties. Visualization tools could be incredibly valuable for analyzing and communicating the spatial variability of uncertainty in a data set, ultimately enhancing both qualitative and quantitative analyses. This study presents an efficient visualization framework for terrestrial laser-scanning (TLS) point cloud uncertainty calculation utilizing the OpenGL Shader Language (GLSL). The methods were tested on four data sets, ranging from a controlled indoor scene containing objects representing simple geometric shapes (e.g., spheres and cones) to a complex forest environment with many types of natural objects. OpenGL shader-based uncertainty visualization was found to aid with the assessment of the effects of modifying models of measurement uncertainty, such as accounting for the nonlinear increase in laser beam radius at short ranges when modeling laser beamwidth-derived uncertainty, as well as range- and angular-based component uncertainties.

The global positioning system (GPS) carrier-phase (CP) technique is an accepted spatial tool for remote, precise, time transfer. However, the day-boundary discontinuity makes exploitation of the full potential of GPS CP time transfer difficult, particularly for a long time (e.g., > 1 day). For this study, we investigated the day-boundary discontinuity using geodetic data solution strategies. First, the edge effect of the satellite orbit and clock product interpolation, which caused a maximum outlier of 0.34 ns at station PTBB, was analyzed because it could eliminate outliers between successive daily clock solutions. Second, the behavior of phase ambiguity was assessed. The inconsistency in phase ambiguity between two daily receiver independent exchange format (RINEX) data points was removed by applying a phase ambiguity strategy. Finally, the day-boundary discontinuity of the receiver clock was evaluated using the GPS CP technique, both with and without inclusion of the two geodetic strategies, at 10 time links between PTBB and the other 10 stations. Compared with the classical CP solution, the outliers for two successive daily solutions could be removed using the edge effect strategy. When the receiver clocks referred to International Global Navigation Satellite System (GNSS) Service time (IGST), the day-boundary jump values without the phase ambiguity strategy were within 1.0 ns, but the jump values decreased to 0.2 ns when the strategy was applied, showing better agreement even at different time laboratories. In terms of the 10 time links, the corresponding day-boundary jump values were within 0.1 and 1.5 ns. By applying the phase ambiguity strategy, the mean jump value was decreased from −0.0999 to −0.0104 ns, and the standard deviation decreased from 0.4667 to 0.0269 ns. The day-boundary jump values at the 10 time links from MJD 57825 to MJD 57837 showed a clear Gaussian distribution.

Spatial information on the seabed is largely obtained by different methods of hydrographic survey. Autonomous underwater vehicles (AUVs) are agile and generate high-quality survey data. Positional accuracy of AUVs is based on deployment of a combination of satellite positioning sensors and attitude sensors, as well as subsea acoustic positioning, platform, and hydrographic survey sensors. Establishing mathematical models to determine the coordinates and respective propagation of the uncertainties among these sensors is necessary to define the potential applicability of AUV hydrographic surveys. The objective of our study was to develop, evaluate, and apply a propagation algorithm for uncertainties associated with the spatial information generated by AUV hydrographic surveys. The results show that the critical components of the propagation model are the acoustic positioning performed via ultrashort baseline (USBL). Selection of the correct configuration of sensors and equipment can ensure that AUV hydrographic surveys meet the International Hydrographic Organization’s (IHO’s) specifications for total horizontal uncertainty (THU) associated with the precision required for minimum standards for hydrographic surveys.

Development of a digital elevation model (DEM) with terrestrial laser scanning (TLS) point cloud data of inadequate resolution and/or completeness will result in a poor-quality DEM with significant gaps. In many cases, this fact can be obscured from the user because spatial interpolation (e.g., generating a surface mesh or kriging) is often performed prior to or during DEM creation, resulting in a seamless DEM in which data gaps in the source TLS data have been filled in. However, evaluating the completeness of DEMs created directly from the point cloud data provides more feedback regarding the suitability of a given TLS point cloud for supporting a specified DEM resolution. An empirical DEM completeness database and associated TLS acquisition planning tool is proposed that can assist in optimizing TLS survey parameters (quantity of scans and scanning resolution) for achieving a high-quality DEM of specified resolution and completeness.