Journal of Surveying Engineering

This investigation introduces a rigorous mathematical transformation of variance–covariance matrices between a global geocentric frame and a plate-fixed geodetic frame. A practical example between the geocentric frame of International GNSS Service 2008 (IGS08) epoch 2005.00 and the geodetic frame North American Datum of 1983 (NAD 83) (2011) epoch 2010.00 was implemented. Although the theory is general, the transformation used here is controlled by the assumptions implicit in the definition of NAD 83. However, the same approach could be extended to future definitions of fixed-plate datums used by geodetic organizations for charting and mapping applications. Consequently, because the transformation between these two specific frames is assumed by definition to be a one-to-one errorless transformation, the uncertainties for the 14 Helmert transformation parameters between the two frames are assumed to be zero. Nevertheless, the formulation is complete and applicable to other specific datum-transformation situations.

The Helmert transformation is used in different procedures in geodesy, photogrammetry, and in general in geomatics. The assessment of the accuracy of the transformation, and in particular of the transformed coordinates, is often critical. In this paper, a new overall quality index describing the accuracy of the transformed points is proposed. This index was derived from the spectral radius of the variance-covariance matrix of the transformed coordinates by writing an expression that represents an upper bound of this quantity. The proposed index is fast to compute and expresses the extent of the uncertainty propagation in a clear and synthetic way. The paper presents the rationale behind the choice of the index and the algebraic steps for its computation. Finally, two examples, one using synthetic data and one involving the coregistration of a point cloud acquired with a laser scanner, are presented.

A research project called ELEVATION (Evaluation of the HelLEnic Vertical Network in the FrAme of the European SysTems and Control Networks InterconnectiON—Application in the Areas of Attica and Thessaloniki) for the validation of the Hellenic vertical network is currently in progress. Two investigation areas in central and northern Greece were chosen for the project. The areas include several benchmarks of the national trigonometric and leveling networks. In the current research, static global positioning system (GPS) observations as well as classical terrestrial leveling were performed to assess the internal accuracy of the two networks. This paper presents some of the numerical tests based on GPS and leveling measurements and outlines the goals of the project. The strategies followed in the processing of GPS data are presented, with emphasis on their future use within this project. GPS observations were processed using various commercial as well as scientific software packages to examine the influence of the processing algorithms on the final results. Significant differences between the results of the various software packages were revealed, particularly in the case of challenging observation conditions. Finally, comparisons of the estimated geoid heights at GPS benchmarks (BMs) to Earth Gravitational Model 2008 (EGM2008) geoid information are presented as a first step toward the evaluation of the Hellenic vertical network. These comparisons indicate that the two investigation areas are of different internal accuracy, namely, 8.3 and 15.8 cm in terms of the standard deviation of the differences at the Attica and Thessaloniki test areas.

Point-based data-acquisition technology in traditional survey engineering does not provide complete data about mining-induced subsidence basins. To overcome these shortcomings, this research applied light detection and ranging (LIDAR) data, obtained with a terrestrial laser scanner (TLS) for monitoring the surface deformation of mining areas, to acquire full data about mining-induced subsidence basins. First, to improve the organization efficiency of LIDAR data, the decimal Morton code–based indexing method was proposed for discrete-grid indexing to organize LIDAR data according to original point coordinates, to avoid the generation of grids without data, and to build a topological relationship among scattered points. Thus, this approach enabled highly efficient access of LIDAR data and restoration of coordinates for each point. In the end, the processed data were applied in engineering practice. The subsidence curves of two sections of the subsidence basin, in both strike and dip directions measured with a high-grade control survey, were compared with the subsidence curves extracted from the LIDAR data. The good coincidence effect suggests that using LIDAR data to build the subsidence basin model can result not only in richer surface-deformation information than the traditional methods but also in higher monitoring precision.

Road profile extraction and analysis are essential tasks in transportation asset management. Current approaches use vehicle-borne laser sensors in order to precisely measure the variations in elevation along a specific route. However, a complicated sensor mechanism, such as in the mobile light detection and ranging (LiDAR) system, is involved and the resulting quality is compromised owing to multiple factors. In this study, an image-based approach for extracting road profiles is proposed. It requires only a single camera sensor and a low-cost laser module and is capable of collecting road profiles along both the longitudinal and transverse directions. A detailed methodology is first presented in this paper, followed by a simulation evaluation and a case study. The case study illustrates that the quality of the extracted profiles based on the proposed approach achieves millimeter accuracy. Consequently, an accurate and cost-efficient road profile analysis becomes possible when the proposed approach is implemented.