Journal of Surveying Engineering

In 1986, Canada, Greenland, and the United States adopted the North American Datum of 1983 (NAD 83) to replace the North American Datum of 1927 as their official spatial reference system for geometric positioning. The rigor of the original NAD 83 realization benefited from the extensive use of electronic distance measuring instrumentation and from the use of both TRANSIT Doppler observations and very long baseline interferometry observations. However, the original NAD 83 realization predated the widespread use of the global positioning system and the use of continuously operating reference stations. Consequently, NAD 83 has evolved significantly in the United States since 1986 to embrace these technological advances, as well as to accommodate improvements in the understanding of crustal motion. This paper traces this evolution from what started as essentially a two-dimensional (2D) reference frame and has been progressing toward a four-dimensional (4D) frame. In anticipation of future geodetic advances, the U.S. National Geodetic Survey is planning to replace NAD 83 about a decade from now with a newer, more geocentric spatial reference system for geometric positioning.

This contribution reviews a few basic concepts of optimization and design of a geodetic network. Proper assessment and analysis of networks is an important task in many geodetic-surveying projects. Appropriate quality-control measures should be defined, and an optimal design should be sought. The quality of a geodetic network is characterized by precision, reliability, and cost. The aim is to present a few case studies that have been designed to meet optimal precision and reliability criteria. Though the case studies may be of interest to the geodetic community in their own right, the aim is to gain insight into the general optimization problem of a geodetic network. This is also potentially of interest for educational purposes. The case studies include a zeroth-order design to improve the precision of the network points in a traverse network and a first-order design to meet the high reliability and maximum precision criteria in a geodetic network. It is shown that not only the configuration of the network but also the type of the observations used can affect the design criteria. For example, the case studies presented show that the optimal shape of the trilateration network (intersection with distances) can result in a weak network in the sense of reliability and precision if the observations are replaced by angles rather than distances (triangulation network). In close relation to the optimization problem of a geodetic network, the global positioning system satellite configuration is also optimized for a particular case that provides the minimum value of the geometric dilution of precision.

Geodetic network design and optimization is a very well-known concept in geodesy. However, in many cases, the available geodetic network configuration with respect to the estimation model is insufficient because of the physical and financial limitations. For the case of estimating the datum transformation parameters between two datums, the colocated points are only an unevenly and inhomogenously distributed subset of the available national/regional networks. Because the transformation parameters are defined with respect to an earth-centered, earth-fixed (ECEF) frame, very limited geographic coverage of the national/regional networks often leads to a weakly multicollinear estimation problem. Such limited geographical coverage is often coupled with the intrinsic geometrical distortions as well as the relatively lower precision of the observations, in particular, when transforming a terrestrial network into a space-based network. In such cases, the individual parameters become highly correlated and oversensitive to the network configuration, and the individual transformation parameters cannot be estimated reliably. In this study, the concept of an idealized three-dimensional (3D) regional network geometry is introduced, its inverse cofactor matrix is analytically derived, and a regularized estimation method based on the inverse cofactor matrix of an ideal network distribution is presented to deal with the weakly multicollinear datum transformation problem. The efficiency of the proposed method is shown in three realistically simulated networks. The proposed method outperforms the standard least squares in terms of mean square error (MSE) and reduces the correlations among the parameters.

High-precision (centimeter-level) real-time kinematic precise point positioning (PPP-RTK) becomes feasible when using precise corrections, as received from a regional Continuously Operating Reference Station network. These network corrections comprise (biased) satellite clocks, (biased) satellite phase biases, and ionospheric delays, where the latter ones are interpolated to the approximate location of the PPP-RTK receiver. Thus far, very fast PPP-RTK integer ambiguity resolution performance has been reported based on dual-frequency Global Positioning System (GPS) data. The availability of ionospheric corrections enables one to carry out PPP-RTK using a single-frequency receiver. Despite that single-frequency integer ambiguity resolution based on a single epoch of data cannot often be successful, fast integer ambiguity resolution is possible when accumulating a short time span of data, assuming that the ambiguities are time constant. In this paper, results of the performance of single-frequency PPP-RTK for both a high-grade geodetic receiver and a low-grade mass-market receiver are presented. The experiments have been conducted based on corrections determined from the GPS Network Perth. The conclusion reads that single-frequency PPP-RTK integer ambiguity resolution is feasible, even using a low-cost receiver: following an initialization time of about 4 min on average, the correct integers can be resolved in real-time, thus providing centimeter-level positioning.

This research provides a performance test of terrestrial light detection and ranging (LIDAR) and multibeam echo sounder scanners integrated with Global Navigation Satellite System/Inertial Navigation System positioning and orientation on a survey vessel platform. To measure the accuracy of the data, experiments were designed to allow the LIDAR and sonar scanners to acquire scans of a control target that extended above and below the water surface. The scans were acquired under normal and induced conditions expected in a marine survey environment, such as variations in speed, range, motion, and orientation. SD, root-mean-square error (RMSE), and mean were computed across all data sets for each experiment. Horizontal RMSE values of 0.06 and 0.03 m were achieved for the LIDAR and sonar data, respectively. Vertical RMSE results of 0.04 m were found for both data types. These results were comparable with previous mobile mapping research involving similar systems. Contributing uncertainty and error sources were analyzed and discussed.

A 2010 survey of terrestrial laser scanner (TLS) usage among state highway agencies indicated that TLS is being increasingly used for highway construction applications among transportation agencies in the United States and Canada. To observe variations in TLS measurements for typical highway conditions, two roadway sites were studied; a 20-year-old asphalt surface and a new concrete surface. Repeated scans were conducted using a Leica ScanStation II to investigate the effects of pavement surface type and reflectance, point density, number and layout of targets, and survey method for establishing control points. Typical target arrangements were not found to greatly affect the resulting scan data for the equipment used in the study. It was observed in this case study that the collected TLS data demonstrated better relative elevation results based on the control and checkpoints established using total stations than on the control and checkpoints established using a real-time kinematic global positioning system. When using the Leica ScanStation II, reflectance of a sample of typical concrete pavement was not observed to vary greatly between 1-month-old and 1-year-old surfaces. Reflectance of asphalt pavement was observed to vary significantly between several examined surfaces ranging from new to 20 years old.