Journal of Surveying Engineering

This work addresses the issue of fitting a geometrical shape to the Hierapolis theater near the city of Denizli, Turkey. The aim of the study was to determine the geometrical shape of the theater that would best fit the set of measured site data points. The geometrical form of the theater was surveyed by using an electronic total station instrument. Because theater rings are generally elliptical in shape, the well-known ellipse-fitting algorithm was presented for computing the geometrical parameters. In this study, the authors plan to analyze the fitting algorithm presented, determine the best-fitting geometrical shape (e.g., an ellipse, a circle) to the Hierapolis theater, and characterize its features. Because the fitting accuracies are not sufficient to decide which geometrical shape is appropriate, a statistical testing procedure was applied to identify statistical differences between the related geometries. The most probable geometrical shapes for this purpose were determined with the use of the statistical equivalence test.

Subsidence and geometry deformation monitoring are essential for safe transportation on a high-speed railway. Terrestrial laser scanning (TLS) is able to collect dense three-dimensional point data from the survey scene and achieve highly accurate measurements; therefore, it is considered to be one of the most promising surveying techniques for railway track geometry deformation monitoring. This paper proposes a new approach that uses TLS to detect subsidence and irregularities in a track by fitting boundaries of the cross section of the track. In addition, for a section of local railway, an outdoor experiment was performed to ascertain the feasibility and accuracy of this method. The deformations detected with TLS were compared with the field measurements gathered with other methods such as those from a track inspection car. The results indicate that the subsidence difference between TLS and precise leveling is 2–3 mm, and the difference in the geometric parameters of the tracks is 1–2 mm. Finally, the possible causes of error involved with TLS are discussed.

This study investigated long-term land subsidence derived from borehole extensometer and Global Positioning System (GPS) observations from Addicks, a suburb located in West Houston, Texas. The Addicks borehole extensometer was built in 1974 by the USGS. Two GPS stations were installed at this site in 1993 and 1996, respectively. One GPS antenna (ADKS) is mounted on the inner pipe of the extensometer borehole, which is firmly anchored 549 m below the land surface. Another GPS antenna (PA05) is mounted on a permanent antenna pole anchored 6 m below the land surface. The horizontal distance between these two GPS antennas is 50 m. Continuous GPS data collected from the deeply anchored GPS antenna indicate that the bottom of the borehole has been stable over the past 20 years (1993–2012). Hence the compaction derived from the borehole extensometer data represents the total subsidence at this site, which should be approximately equivalent to the vertical displacement (subsidence) recorded by the shallowly anchored GPS antenna (PA05). In this study, the vertical displacement time series recorded by the shallowly anchored GPS antenna are regarded as the true values to assess the accuracy of the subsidence time series recorded by the extensometer. The authors’ analysis indicates that the difference between the cumulative subsidence measured by the extensometer and the GPS antenna (PA05) is less than 5 mm for a 17-year span (1996–2012). The RMS of the residuals of the monthly subsidence time series derived from the extensometer and GPS antenna (PA05) data over 13 years (2000–2012) is 2 mm.

With the advent of global navigation satellite systems (GNSSs), many national geodetic datums have been established with modern technology and referenced to a specific epoch of the international terrestrial reference frame (ITRF) definition. Following the static datum concept, the datum remains unchanged after its publication, which consequently creates problems in datum maintenance. In the recent update of TWD97, the national datum presently used in Taiwan, the resurvey coordinates are transformed back to the original frame but expressed in a recent epoch. In this study, the uncertainties resulting from the transformation between ITRF definitions in the region of Taiwan were investigated. Based on error propagation, a standard error of $\pm 7\hspace{0.17em}\text{cm}$ was estimated due to the transformation of the TWD97 coordinates between ITRF2005(2010.0) and ITRF94(2010.0). The uncertainties propagated from transformation parameters are more significant than those from station coordinates and velocities, and the uncertainty expands with the time interval. The SD is $\pm 1.1\hspace{0.17em}\text{cm}$ for the transformation between ITRF2005 and ITRF2000. Considering that the uncertainty between later definitions is much smaller than transforming to ITRF94, it may be preferable to replace the ITRF94 with a modern ITRF definition, at least ITRF2000, for the next TWD97 datum maintenance.