Journal of Surveying Engineering

Forum papers are thought-provoking opinion pieces or essays founded in fact, sometimes containing speculation, on a civil engineering topic of general interest and relevance to the readership of the journal. The views expressed in this Forum article do not necessarily reflect the views of ASCE or the Editorial Board of the journal.

Agricultural and forestry operations significantly affect land morphology. Monitoring topographical and morphological changes is important in agriculture, forestry geomorphology, and soil sciences for improving land management. Tillage is one of the most common land management methods, which aims at loosening the soil and optimizing edaphological conditions. This paper used point cloud data from a mine reclamation project in Brisbin, Pennsylvania that employed deep tillage methods to improve soil structure. In recent years, point cloud technologies such as small unmanned aerial system (sUAS) photogrammetry often has been used to support agricultural and forestry operations, and to provide detail estimation of land morphological changes. This paper assessed the effectiveness of sUAS and terrestrial laser scanning (TLS) to estimate changes in soil surface elevations after deep tillage treatment. A traditional survey with total stations was used as a reference to assess the performance of each method and gain insights. Several parameters that affect the accuracy of such multiepoch surveys were examined, including georeferencing, sUAS camera self-calibration, sUAS software, ground classification methods, the effect of vegetation on point cloud accuracy, the effect of distance from scanner on TLS point cloud accuracy, and merging scenarios to utilize the advantages of both sensors. Results indicated that in areas with low vegetation, both methods can provide reliable land surface estimation; however, in areas with dense and high vegetation, the two methods had considerable vegetation penetration issues. In TLS surveys, the error increased with increasing distance from a scanner setup. TLS achieved higher accuracy than sUAS surveys up to 5 m from a scanner setup, whereas at distances between 5 and 10 m from a scanner setup, accuracy was comparable for the two methods, and beyond 10 m from a scanner setup sUAS achieved better accuracy than TLS. Furthermore, this paper investigated the benefit of using a prior camera self-calibration, estimated on the same site from the first sUAS data set before tillage, versus estimating a new self-calibration for the second sUAS data sets after tillage. Results showed that a prior self-calibration is essential when the number of ground control points (GCPs) is low, i.e., fewer than four GCPs when Global Navigation Satellite System real-time kinematic (GNSS-RTK) is available, and fewer than eight GCPs when GNSS-RTK is not available. Insights gained from this study can assist in improving surveying planning, and they are important to surveyors and practitioners who are employed in agricultural and forestry applications.

Global Positioning System (GPS) technology is reported in the literature as a reasonable alternative for the structural health monitoring (SHM) of bridges. However, more validations of GPS technology must be performed to extract the associated risk of bridges, particularly applying probabilistic concepts. This paper presents a probabilistic approach to evaluating the safety of bridges using real-time dynamic displacements obtained via geodetic-grade GPS receivers. The implementation of the probabilistic approach is demonstrated by the evaluation of the serviceability condition of a real-scale bridge. The structural evaluation involved the continuous extraction of GPS displacement data over the course of 1 h at three different periods of the day from Monday to Sunday. A comprehensive probabilistic study is developed based on dynamic displacements in terms of reliability index and probability of failure. Finally, based on the findings documented in this paper, the detection of unsafe serviceability conditions of bridges is possible by integrating GPS technology and the probabilistic approach presented in this research, which may help to inform decisions about the improvement or retrofit of bridge structures.

This study aims to develop a new real-time zenith tropospheric delay (ZTD) model over Africa, namely the AFRC-Trop model. In order to estimate the ZTD, global positioning system (GPS) observations from 14 reference stations are processed in the precise point positioning (PPP) mode using the international global navigation satellite system (GNSS) real-time service (IGS-RTS) products. Then, the Kriging interpolation technique is used to compute the ZTD for a $1°\times 1°$ grid at a $1\text{-}\mathrm{h}$ time interval. The AFRC-Trop-derived ZTD is validated with respect to the IGS and the Center for Orbit Determination in Europe (CODE) tropospheric products counterparts. The computed ZTD are compared as well with the very-long-baseline interferometry (VLBI) tropospheric products. Additionally, the proposed model is validated with the empirical tropospheric models, namely the University of New Brunswick (UNB3m) and the Global Pressure and Temperature 2 Wet (GPT2w) models. The findings indicate that the newly developed AFRC-Trop model shows good agreement within a few centimeters with the IGS, CODE, VLBI, UNB3m, and GPT2w models.

The BeiDou Navigation Satellite System (BDS) has used the BeiDou Coordinate System (BDCS) as its geodetic reference system since December 2017. After a brief description of the background, definitions of the origin, scale, and orientation of BDCS are given, which are consistent with China’s Geodetic Coordinate System 2000 (CGCS2000). Then the first realization of the BDCS aligning with the International Terrestrial Reference Frame 2014 (ITRF2014) is addressed. Coordinates at epoch 2018.0 and velocities at eight BDS monitoring stations were obtained achieved by processing four-phase GPS data for a global navigation satellite system (GNSS) network, including the monitoring stations, and by the frame alignment and linear regression fitting of station coordinate series. Assessment of the precision of the coordinates and Helmert parameters with respect to ITRF2014 reveals that the differences between the first frame of BDCS and ITRF2014 are less than 1 cm, which is compatible with WGS84 (G1762), PZ-90.11, and the latest Galileo terrestrial reference frame.

Until a few years ago, a precise survey was only possible using global positioning system (GPS) and Global’naja Navigacionnaja Sputnikovaja Sistema (GLONASS) constellations, but the result was not guaranteed under conditions of poor sky visibility, as in urban canyons. Currently, the number of Global Navigation Satellite System (GNSS) satellites in orbit has strongly increased thanks to the great evolution of the Galileo and the Beidou constellations. In this paper, we investigate the impact of using different constellations and their combinations, in static positioning with the classical differencing approach. For this purpose, two distinct baselines of different lengths (10 and 60 km) were processed using commercial software over a period of one year (2018.24–2019.24). Data were acquired by permanent stations belonging to the European Permanent Network (EPN) network providing $24\text{-}\mathrm{h}$ observing sessions. Two datasets were tested, one consisting of $24\text{-}\mathrm{h}$ Receiver Independent Exchange Format (RINEX) files and the other considering only $2\text{-}\mathrm{h}$ sessions of data acquisition. In both cases, a one-year-long time span has been considered. The baselines were processed considering each of the four GNSS constellations and a series of combinations, for a total of eight solutions. Results have been evaluated looking at the accuracy and repeatability of the coordinates, together with the main constellation parameters. During the analyzed period the number of contemporary visible satellites of the BeiDou constellation was still too poor over the considered area, and therefore this constellation did not provide comparable precisions in respect to the others. Positioning precision provided by the Galileo constellation has shown to be very close to those given by GPS or GLONASS, with a significant difference only on the height component, especially in the case of processing $2\text{-}\mathrm{h}$ data. As for $24\text{-}\mathrm{h}$ observing sessions, the use of multiconstellation observables actually leads to small improvements in precision with respect to the use of GPS data only, mainly appreciable considering the vertical component. The GPS-Galileo combination gives quite the same performances of the GPS-GLONASS one, but it can potentially take advantage of the integrity message provided by the European constellation.

In our society, geospatial data are used for multiple purposes, and their use has grown exponentially in recent decades, especially with the emergence of COVID-19. In this sense, universities play a key role in the geospatial domain from two points of view: the formation of students in this field in society, and the transfer and communication of knowledge. Considering the university-age population in Spain, a study was carried out in autonomous communities on the training provided by degrees that educate future spatial data managers (i.e., Bachelor Degree in Engineering in Geomatics and Surveying and Bachelor Degree of Geography) and the disciplines in which geospatial data are treated indirectly. The results show that universities offer two degrees providing direct training and seven degrees providing indirect training in geospatial data management per 100,000 inhabitants of university age. A high correlation of ${\mathrm{R}}^2=0.84$ has been found between the number of degrees that provide direct training and the number of geospatial services offered by Spanish universities, and most of these degrees and resources are offered by public universities. Although there are good prospects for the future of the geospatial industry, the number of students pursuing these degrees is decreasing by 5% while the number of students enrolled in all degrees in the country has increased by 4.3%. It seems important to reorient more training towards the current direction of the geodata market and online training.

Regions at high elevations may require specific mapping solutions other than the conventional ellipsoid-to-grid projections, which produce large discrepancies between ground and projected distances. These particular solutions are known as low-distortion projections (LDPs). They can be realized by using an elevated ellipsoid (EE) or a constant-height surface (ChS) above the ellipsoid as the reference surface, or by means of a scaled projection. No conformal projections have been derived thus far for the ChS-to-plane transformation. This work aims to solve this problem by deriving the formulation of direct and transverse Mercator-type projections for ChS-to-plane conformal mapping.