Journal of Surveying Engineering

The aim of this study is to develop a method to mitigate the ionospheric delay bias in long baseline differential global positioning system (GPS). The ionospheric delay is the main source of error when single frequency GPS receivers are involved in surveys with baselines which exceed a few tens of kilometers. This article presents a technique that estimates the vertical total electron content (VTEC) in several continuously operating reference stations (CORS) and computes the slant total electron content (STEC) for the receiver of unknown coordinates. VTEC was obtained from the La Plata ionospheric model and an interpolation strategy was implemented in order to calculate STEC values. Networks covering different areas and baseline sizes are studied. The strategy presented in this article could be particularly useful when the accuracy of one decimeter is required and reference stations used are a few hundred kilometers away since it provides a 50% improvement in position accuracy.

The purpose of the research was to compare measuring orthometric heights using differential leveling, static global positioning observations, and real-time kinematic (RTK) Global Positioning System (GPS) observations in the vicinity of the University of Conn. campus. Height observations were recorded at temporary and permanent monuments using differential leveling, static GPS, and RTK. Heights at permanent monuments with published elevations were observed using each method and served as control and to check the quality of all measurements. Three-dimensional reference ellipsoid coordinates derived from GPS observations and published orthometric heights were used to create local geoid models, which were then used to convert ellipsoid heights observed with the static GPS and RTK to orthometric heights. The resulting values were used to compare between the measuring methods. In general, static GPS performed better than RTK. Several polynomial surface models of different orders were fitted to the geoid heights, from a constant up to a quadratic. No meaningful distinctions could be drawn between the models indicating that, for a small geographical area, shifting the national geoid model, GEOID03, by a constant vertical amount performs as well as the more complicated approaches. Experience showed that multiple, independent RTK observations on the same day are not sufficient to ensure freedom from systematic errors.

Total stations were developed about $20\text{years}$ ago and, since then, their measuring performance has been very much improved. However, a surveyor’s skills are still essential for precise measuring as is required for most surveying tasks. The next total station system should focus on obtaining the required accuracy and quality results by any user at the same speed as if the work were done by a skilled surveyor. Here, we have attempted to develop a new system which utilizes photogrammetric images that supply additional information. Field test results presented in this paper show that the new system displays images overlaid in real time with graphics and synchronized with a sighting telescope, can reduce the number of staff and total man days required for field measurements, and eliminates the need for editing line connections in the postprocessing task. As mentioned above, the new imaging total station system, which utilizes image and graphic data, can give considerable efficiency improvement in the total surveying process compared with conventional systems and methods.

In this study global positioning system (GPS) technology is used to monitor the structural movement of a cable-stayed bridge over the River Tamar in northern Tasmania, Australia. Observed displacements are compared with predicted deflections derived from modeling undertaken with the Space Gass structural analysis software suite. Results show that GPS is successful in quantifying both thermally induced bridge displacements and high frequency transient motion caused by vehicle loading. GPS-derived estimates of the bridge’s short-term dynamic motion correlate well with the predicted model response, providing the ability to verify the model and pose potential improvements to the model configuration. Deflection signatures from GPS show typical displacements on the main span of $54\pm 3.5\mathrm{mm}$ in height, with corresponding longitudinal displacements on the tower structure of $17\pm 2\mathrm{mm}$ . Displacement of the bridge caused by thermal variations is also clearly evident in the data and correlates well with additional external measurements. GPS is a valuable observational tool for monitoring structures and provides a powerful analysis tool for verification and/or improvement of structural design and modeling.

Generating fast and inexpensive digital road maps and databases from high-resolution satellite imagery is becoming possible for various applications. This paper presents a new method for establishing road horizontal alignment using IKONOS $1\mathrm{m}$ spatial resolution imagery. Road extraction algorithms were developed for two types of horizontal curves: Simple circular curves and reverse circular curves. The method requires only two and three unknown parameters for simple and reverse curves, respectively. Unlike existing methods of circle detection, the proposed method performs the search procedures in a much smaller area than the image size and achieves faster computations. The derived curve parameters represent useful inputs into a geographic information system database. The developed method has been tested using IKONOS images for simple and reverse curves. The results show that the proposed method converges in all cases and can be used for accurately establishing road horizontal curves.

Generating road databases from high-resolution satellite imagery is advantageous over traditional methods because of its simplicity and efficiency. Previous research has addressed the extraction of nonspiralled horizontal curves (simple, compound, and reverse curves). All curves were assumed to be circular. This paper presents an approximate method for extracting spiralled horizontal curves. A spiralled horizontal curve consists of a circular curve and a spiral curve at each end that connects the circular curve and the tangent. The spiral curve has a curvature that gradually increases from zero (at the tangent) to the curvature of the circular curve. Because of the symmetry of the spiralled horizontal curve and the semiautomatic nature of the extraction process, the search is three dimensional. Similar to the extraction of nonspiralled horizontal curves, the proposed method performs the search procedures in a smaller area than the image size and achieves faster computations. The method first extracts one side of the road, and a simple procedure for establishing the other side is then applied. The derived curve parameters (circular curve radius, deflection angle, and spiral length) represent useful inputs into a geographic information system database.