Journal of Surveying Engineering

There are two kinds of global test procedures in deformation analysis; ${\chi }^2$-test (CT) and $F$-test (FT). This study discusses their power functions. The CT is more powerful than the other one in an analytical point of view. However, it requires an accurate knowledge on the a priori variance of unit weight. Therefore, in practice, the FT is mostly chosen. Despite its common usage, a ${\chi }^2$-power function is considered in the sensitivity design of deformation networks. It is claimed in this study that the $F$-distribution’s power function should be taken into account, if, in reality, the FT will be applied. Thereby, some boundary values deduced from the noncentral $F$-distribution to be used in sensitivity analysis are computed and tabulated. Furthermore, a simulation for a monitoring network is designed, and it is shown that the mean success rates of the two testing procedures are identical with their own powers known beforehand. This numerical experiment depicts that one should consider the related power function in the design stage, and that each power function gives a realistic probability of how the corresponding test procedure is successful.

Old geophysical surveys [pre–Global Positioning System (GPS)] stand as valuable, largely untapped sources of scientific data. If data from these surveys were in a format that had reasonable accuracy, availability, and ease of access, they could be more widely used. In this paper, a pre-GPS survey is integrated into a modern geographic database, in this case, The National Map (TNM). The ultimate goal is to improve the accuracy, precision, provenance, and ease of access of the geospatial components of archived geophysical data. An unique set of data sources was assembled for this purpose. A comparison of these different data sources indicates that more than 80% of stations were positioned on The National Map within 15 m (horizontal) and 2 m (vertical) of the GPS-derived coordinates for each station within the survey. Although online database coordinate accuracy continues to improve, these results imply that web databases have already matured to a point where it is possible to integrate pre-GPS era survey coordinate data with reasonable positional accuracy.

Range cameras offer great potential for the measurement of structural deformations because of their ability to directly measure video sequences of three-dimensional coordinates of entire surfaces, their compactness, and their relatively low cost compared with other active imaging technologies such as terrestrial laser scanners. Identified limitations of range cameras for high-precision metrology applications such as deformation measurement include the high (centimeter level) noise level and scene-dependent errors. This paper proposes models and methodologies to overcome these limitations and reports on the use of a SwissRanger SR4000 range camera for the measurement of deflections in concrete beams subjected to flexural load-testing. Results from three separate tests show that submillimeter precision and accuracy—assessed by comparison with estimates derived from terrestrial laser scanner data—can be achieved. The high-accuracy range camera results were realized by eliminating the systematic, scene-dependent bias of internal scattering through measurement differencing and by reducing the influence of random errors with temporal and spatial filtering strategies. Additional experiments to validate some of the fundamental modeling assumptions and to explain the possible causes of residual, submillimeter biases in the deflection estimates are also reported.

The objective of this case study is to evaluate the different approximations in the technical literature that are used to compute the variance-covariance matrix of local accuracies. This analysis compares the rigor and validity of the four most common mathematical formulations that are used for computing the variance-covariance matrix of local accuracies, as determined from the original global Cartesian variance-covariance matrix ${\Sigma }_{(x,y,z)}$ of any given three-dimensional network. These empirical results, which are strictly established on the accepted definition of local accuracies (also referred to as relative accuracies), are an attempt to clarify the adopted standards for computing the variance-covariance matrices of local accuracies.

In studies related to ground excavations, glaciers, human brains, or many other branches of science, a need to know often arises regarding the volume of an irregularly shaped object or region in 3D space. An approach using finite elements offers a closed form solution that can accommodate uneven spacing with scattered data points and arbitrary boundaries. Using numerical examples, results from the proposed method are presented and accuracy compared with known solutions.

This paper presents preliminary results to determine small displacements of a global positioning system (GPS) antenna fastened to a structure using only one L1 GPS receiver. Vibrations, periodic or not, are common in large structures, such as bridges, footbridges, tall buildings, and towers under dynamic loads. The behavior in time and frequency leads to structural analysis studies. The hypothesis of this article is that any large structure that presents vibrations in the centimeter-to-millimeter range can be monitored by phase measurements of a single L1 receiver with a high data rate, as long as the direction of the displacement is pointing to a particular satellite. Within this scenario, the carrier phase will be modulated by antenna displacement. During a period of a few dozen seconds, the relative displacement to the satellite, the satellite clock, and the atmospheric phase delays can be assumed as a polynomial time function. The residuals from a polynomial adjustment contain the phase modulation owing to small displacements, random noise, receiver clock short time instabilities, and multipath. The results showed that it is possible to detect displacements of centimeters in the phase data of a single satellite and millimeters in the difference between the phases of two satellites. After applying a periodic nonsinusoidal displacement of 10 m to the antenna, it is clearly recovered in the difference of the residuals. The time domain spectrum obtained by the fast Fourier transform (FFT) exhibited a defined peak of the third harmonic much more than the random noise using the proposed third-degree polynomial model.

Terrestrial laser-scanning (TLS) technology can be used to create a detailed model before and after construction to determine earthwork quantities. Cost-effective implementation of this technology requires that field operations are planned to efficiently acquire sufficient scan data and that data processing is able to filter out off-terrain points to provide an accurate bare earth model. This research developed a workflow for using TLS on road projects and created a customized computer program with a graphical user interface. Scans taken before and after construction were planned using the best available terrain model. Point cloud data were converted to station/offset coordinates for viewing cross-sections and generating the surface. An algorithm was developed, based on the finite element method, to create a surface through the lowest scan points. This surface was converted to a Triangulated Irregular Network (TIN) file, and earthwork quantities were calculated by comparing the TIN of the original terrain to that of the finished project.