Journal of Surveying Engineering

The article presents an original approach to the design of geodetic networks, taking into account quality criteria. This approach is based on the geodetic network design using the methods of multicriteria decision making (MCDM). Based on the design criteria of geodetic networks (accuracy, reliability, and costs), which are known from the literature, a modified, original set of design criteria was adopted. The presented proposals are illustrated with an example of a trilateration network that confirmed the usefulness of the proposed methodology in the design of geodetic networks. Comparative studies of considered network variants were made using four MCDM methods. These were three known methods of multicriteria analysis and one method developed by the author. Sensitivity analysis also allowed indicating methods that give the highest stability of rankings that are the basis for choosing the optimal network.

One of the main concerns during digital elevation model (DEM) evaluation is the number of ground control points (GCP). Accordingly, in this paper, a new method is proposed for calculating the appropriate number of GCPs for DEM evaluation based on a confidence interval (CI) of the root-mean-square error (RMSE). This method was employed to determine the CI of the estimated vertical accuracy of Advanced Land Observing Satellite (ALOS) World 3D-30m (AW3D30), Shuttle Radar Topography Mission (SRTM), and Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) Global Digital Elevation Model (GDEM) Free 30 m resolution global DEMs in mountainous, hilly, flat, and urban regions of two study areas. To provide a more reliable estimation of errors, robust statistical methods, including median, normalized median absolute deviation (NMAD), and Huber’s $\mu$ and $\sigma$ were also investigated. Furthermore, a new formulation was developed to analyze the propagation of the errors in the slope and aspect products of DEM. The results showed that, to evaluate the accuracy of AW3D30, ASTER GDEM, and SRTM with a CI of $\pm 1\mathrm{m}$ and the probability of 99%, in the study area, a minimum number of 2,110, 1,483 and 750 GCPs are required, respectively. The results also showed that, in the flat, hilly, and mountainous study areas, AW3D30 was the most accurate DEM. However, SRTM fit better to the urban study area. Finally, the results of the error propagation analysis illustrated that the slope and aspect errors bore a striking relation to the surface gradient.

To ensure that the high-speed train with speeds from 200 to $350\mathrm{km}/\mathrm{h}$ or even faster can run safely and smoothly, the ballastless or ballast track must have high riding comfort. As the precise control reference of railway track, the surveying control network called base-pile control points III (CPIII) in China must be precise, smooth, and reliable. Therefore, careful field surveying and rigorous internal data checking are both required. However, the reliability of such a significant surveying system is still ambiguous for us, which is obviously not conducive to the effective control of data quality. In this paper, in order to select a feasible method to properly and effectively analyze the gross error separability of a CPIII network, two current separability analysis methods, that is, methods using correlation coefficient and gross error judgment equation (GEJE), are first comparatively analyzed in detail. The results show that the two methods are not only equivalent but also that the GEJE method is more convenient to study gross error separability among multiple observations. Some general regularities of gross error detectability and identifiability that exist in single and multiple observations of the CPIII network are then mined using the GEJE method; moreover, those regular findings are demonstrated using Monte Carlo simulations. The research results will be beneficial for deep understanding of the reliability of the CPIII network and further gross error detection.

The clothoid, also known as Cornu spiral or Euler spiral, is a curve widely used as a transition curve when designing the layout of railway tracks and roads because of a key feature: its curvature is proportional to its length. The classical method to compute a clothoid is based on the use of Taylor expansions of sine and cosine functions, usually starting with zero curvature at the initial point. In this paper the clothoid is presented as the only curve with a constant rate of change of curvature, which parametrization can be obtained by solving an initial value problem. In this initial value problem the curvature at the starting point can be chosen, being able to develop simple, efficient, and accurate algorithms to connect two oriented circumferences by means of clothoids. These algorithms are presented as a useful tool for designing egg and double-egg curves in highway connections and interchanges.

The number of unmanned aerial system (UAS) mapping applications that require high-accuracy data sets have grown significantly in recent years. Indirect georeferencing (IG) requires the establishment of multiple, well distributed ground control points (GCPs) throughout a project site. UAS mapping operations can now use precise navigation trajectories with position and/or orientation observations to replace or augment GCPs. Assisted aerial triangulation (AAT), which uses only airborne camera perspective center (CPC) observations to augment GCPs, is the primary method investigated herein. The objective of this study is to rigorously analyze the impact that each additional GCP in UAS structure from motion (SfM) photogrammetric processing has on the spatial accuracy of UAS-derived orthophotos and digital surface models (DSMs) when comparing AAT to IG. Three separate flights with two different cameras were flown over a project site that had a network of nine GCPs and 70 additional checkpoints (CPs). The authors carried out 29 unique processing trials for each flight, varying the georeferencing method and the quantity of GCPs used. American Society of Photogrammetry and Remote Sensing’s (ASPRS’s) Positional Accuracy Standards for Digital Geospatial Data provided reporting metrics to evaluate the derived orthophoto and DSM from each processing trial. UAS SfM processing using AAT with minimal to no augmenting GCPs provided high spatial accuracy products that met or exceeded more traditional workflows reliant on IG. When using AAT, the inclusion of at least one GCP improved vertical spatial accuracy relative to processing trials by using airborne positioning alone. To ensure the focal length was resolved during camera self-calibration, the inclusion of at least two high-accuracy GCPs in the simultaneous bundle block adjustment (SBBA) is recommended.