Journal of Surveying Engineering

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Weakly Multicollinear Datum Transformations

Bahadır Aktuğ

Journal of Surveying Engineering doi:http://dx.doi.org/10.1061/(ASCE)SU.1943-5428.0000086

Posted ahead of print 10 March 2012

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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 due to the physical and financial limitations. For the case of estimating the datum transformation parameters between two datums, the co‐located points are only an unevenly and inhomogenously distributed subset of the available national/regional networks. Since the transformation parameters are defined with respect to an ECEF (earth‐centered, earth‐fixed) 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 to a space‐base 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 idealized 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 Squared Error (MSE) and reduces the correlations among the parameters.

Single‐Frequency Integer Ambiguity Resolution Enabled Precise Point Positioning

Dennis Odijk, Peter J. G. Teunissen, and Baocheng Zhang

Journal of Surveying Engineering doi:http://dx.doi.org/10.1061/(ASCE)SU.1943-5428.0000085

Posted ahead of print 8 March 2012

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High‐precision (cm‐level) Real‐Time Kinematic Precise Point Positioning (PPP‐RTK) becomes feasible when using precise corrections as received from a regional CORS 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. So far very fast PPP‐RTK integer ambiguity resolution performance has been reported based on dual‐frequency 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 contribution we present for the first time results of the performance of single‐frequency PPP‐RTK for both a high‐grade geodetic receiver and a low‐grade mass‐market receiver. 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 minutes on average the correct integers can be resolved in real‐time, thus providing cm‐level positioning.

Operational Considerations for Terrestrial Laser Scanner Use in Highway Construction Applications Case Study

Wei Hong Johnson, Ph.D., P.E. (SC) and Andrew M. Johnson, Ph.D., P.E. (SC)

Journal of Surveying Engineering doi:http://dx.doi.org/10.1061/(ASCE)SU.1943-5428.0000084

Posted ahead of print 10 February 2012

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Based on the results of a 2010 survey of terrestrial laser scanner (TLS) usage among state highway agencies, 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 twenty‐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 control and check points established using total stations than on control and check points established using real‐time‐kinematic GPS. When using the Leica ScanStation II, reflectance of a sample of typical concrete pavement was not observed to vary greatly between one month and one year old surfaces. Reflectance of asphalt pavement was observed to vary significantly between several examined surfaces ranging from new to twenty years in age.

The Evolution of NAD 83 in the USA: A Journey from 2D Towards 4D

Richard A. Snay

Journal of Surveying Engineering doi:http://dx.doi.org/10.1061/(ASCE)SU.1943-5428.0000083

Posted ahead of print 1 February 2012

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In 1986 Canada, Greenland, and the United States of America (USA) 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 USA 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 2D reference frame and has been progressing towards a 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.

Estimation of Focal Length Variations of a 100 m Radio Telescope's Main Reflector by Laser Scanner Measurements

Christoph Holst, Philipp Zeimetz, Axel Nothnagel, Wolfgang Schauerte, and Heiner Kuhlmann

Journal of Surveying Engineering doi:http://dx.doi.org/10.1061/(ASCE)SU.1943-5428.0000082

Posted ahead of print 1 February 2012

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Due to gravitation, the main reflector of a radio telescope underlies a deformation which causes a change in focal length depending on the variations of the elevation angle of the telescope. In order to estimate these gravity dependent deformations of the main reflector of the 100m radio telescope at Effelsberg, Germany, we propose a measurement concept based on a laser scanner being mounted upside‐down on the subreflector. The measurements which have been performed at seven different elevations between 90° and 7.5° are used to estimate the focal length variation of the main reflector parameterized by a rotational paraboloid. To guarantee reliability of the adjustment, we perform an orthogonal distance regression (ODR) rather than a classical least squares adjustment in a Gauss‐Helmert model. We formulate the independence of the focal length estimation from the absolute position and orientation of the main reflector in space as a requirement for a reliable adjustment approach. Our investigations attest the ODR a superior reliability with regard to this criterion. A three‐step adjustment procedure based on an alteration of the ODR and several outlier eliminations is used to determine the variations of the focal length due to gravitation. The estimated focal length decreases by a maximum of 12.6mm when tilting the reflector from 90° to 7.5° elevation angle. The post‐fit discrepancies between the best‐fit paraboloid and the reflector's surface are Gaussian distributed within the accuracy of the measurements which supports the assumption of a homologous deformation of the main reflector.

Basic Concepts of Optimization and Design of Geodetic Networks

A. R. Amiri‐Simkooei, M. ASCE, J. Asgari, F. Zangeneh‐nejad, and S. Zaminpardaz

Journal of Surveying Engineering doi:http://dx.doi.org/10.1061/(ASCE)SU.1943-5428.0000081

Posted ahead of print 1 February 2012

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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 looked for. The quality of a geodetic network is characterized by precision, reliability, and cost. We aim to present a few case studies that have been designed to meet optimal precision and reliability criteria. Though the case studies can be of interest into the geodetic community in their own rights, we aim 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 zero 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, we also optimize the GPS satellites configuration for a particular case that provides the minimum value of GDOP.

A New‐Median‐Approach to Define Configuration Weakness of Deformation Networks

Serif Hekimoglu and Bahattin Erdogan

Journal of Surveying Engineering doi:http://dx.doi.org/10.1061/(ASCE)SU.1943-5428.0000080

Posted ahead of print 14 January 2012

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The main problem in the conventional deformation analysis (CDA) is that if there is more than one displaced point in a given monitoring network, the least squares estimation (LSE) smears the disturbing effects of the displaced points over all other points. Therefore, only one displaced point can be detected successfully by using CDA. If the number of displaced points increases, the success of detecting these points decreases significantly. This weakness of CDA originates mostly from the configuration of the monitoring network. In order to detect the weakness of any monitoring network, a new approach that is based on applying median of differences between the measurements of epoch I and epoch II related to the same point has been developed. In this wise, the displaced points which are detected by CDA can be checked whether these points are actually displaced or not from the point of view of the configuration weakness of the network. To design a capable deformation network, that has at least minimum configuration isolating smearing effect of LSE, makes it possible to detect displaced points with highest success.

OPUS for Horizontal Subcentimeter‐Accuracy Landslide Monitoring: A Case Study in the Puerto Rico and Virgin Islands Region

Guoquan Wang and Tomás Soler, M. ASCE

Journal of Surveying Engineering doi:http://dx.doi.org/10.1061/(ASCE)SU.1943-5428.0000079

Posted ahead of print 2 January 2012

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This study demonstrated the usefulness of an approach based on the Online Positioning User Service (OPUS) provided by the National Geodetic Survey (NGS) of the National Oceanic and Atmospheric Administration (NOAA) to process GPS data and conduct long‐term landslide monitoring in the Puerto Rico and Virgin Islands Region. Continuous GPS data collected at a creeping landslide site during two years were used to evaluate different scenarios for landslide surveying: continuous or campaign, long duration or short duration, morning or afternoon (during different weather conditions). OPUS uses the Continuously Operating Reference Station (CORS) network managed by NGS as control points and user collected data to solve for the position of the occupied station (rover). As of July 2011, there are 19 NGS CORS sites in the Puerto Rico and Virgin Islands region. This dense GPS network provides a precise and reliable reference frame for subcentimeter‐accuracy landslide monitoring in this region. OPUS static solutions (OPUS‐S) for sessions as short as 4 hours, and OPUS rapid static solutions (OPUS‐RS) for sessions as short as 15 minutes, can achieve subcentimeter horizontal accuracy if the collection of data during extreme weather conditions is avoided. The uncertainty (peak‐to‐peak error) reported by a single OPUS‐S solution differs from the “true” accuracy by a factor of 1.7 for the horizontal components and 1.3 for the vertical component. The uncertainty reported by a single OPUS‐RS solution differs from the accuracy by a factor of 1.4 for horizontal components, while the uncertainty of vertical component statistically agrees with the vertical accuracy. This study also indicated that rainfall events can seriously degrade the performance of high‐accuracy GPS. Field GPS landslide surveying should avoid rainfall episodes when accompanied by thunderstorms and the passage of detrimental weather fronts. Once appropriate precautions are taken, the results of this investigation show that OPUS‐S and OPUS‐RS are ideal alternative tools for subcentimeter‐accuracy landslide monitoring.

Approximation of the Curvature of the Parthenon Stylobate using Least Squares Techniques

George Georgopoulos, Dr. and Elisavet Telioni, Dr.

Journal of Surveying Engineering doi:http://dx.doi.org/10.1061/(ASCE)SU.1943-5428.0000078

Posted ahead of print 21 December 2011

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The subtle curves of the masterpiece of ancient Greece, the Athenian Parthenon, have been the object of many investigations of scientists of various disciplines. A lot of discussion has taken place about the shape of the monument's curved stylobate surface and the kind of mathematical curve that best describes it. In this paper a new approximation of the stylobate's curves is presented, using its transverse and longitudinal inclinations estimated from the measured uneven heights of the lowermost drums of the peristasis columns. Two kinds of conic sections: a circle and a parabolic curve were estimated, using least squares techniques and their appropriateness was checked through their correlation coefficients. Finally the minimum detectable constructional inaccuracy is estimated.

Identifying the Relationship between GPS Data Quality and Positioning Precision: A Case Study on IGS Tracking Stations

Ta‐Kang Yeh, Yi‐Da Chung, Chien‐Ting Wu, Chuan‐Sheng Wang, Kefei Zhang, and Chieh‐Hung Chen

Journal of Surveying Engineering doi:http://dx.doi.org/10.1061/(ASCE)SU.1943-5428.0000077

Posted ahead of print 21 December 2011

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The number of Global Positioning System (GPS) tracking stations is increasing, primarily because the stations are multifunctional: in civil engineering, they can be used for precision positioning; in earth sciences, they can be used to monitor faults and earthquakes; and in atmospheric sciences, they can be applied to predict perceptible water vapor. Currently, there are more than 400 GPS stations in Taiwan, but the data obtained through such stations are not being assessed carefully. Experienced scientists and engineers examine the data in advance to see if they qualify for research purposes. However, inexperienced users can adopt poor quality data that eventually lead to inaccurate research results. Of the observation stations with receivers that were renewed between 2006 and 2008 in the International GNSS Service (IGS) Network, four stations, ZIMM, BOR1, NRC1 and NICO, were selected to be the subjects of this research. Six indices of data quality were observed to calculate the quality of data obtained before and after receiver renewal. Then, analyses were conducted to understand the relationship between the quality indices and positioning precision. Results showed that, after receiver renewal, the positioning precision of the four stations was improved by 1‐19%. Therefore, positioning precision is positively affected by the six data quality indices. It was also discovered that receiver clock error was the most critical factor among the six indices. In conclusion, if data quality control can be applied to GPS tracking stations, the data obtained will be more reliable for research purposes, and the accuracy of subsequent engineering and science measurements will be improved.

Sensitivity Analysis for the Principal Strain Parameters of a Deformation Monitoring Network

Jen‐Yu Han, Jenny Guo, and Ze‐Yuan Zheng

Journal of Surveying Engineering doi:http://dx.doi.org/10.1061/(ASCE)SU.1943-5428.0000076

Posted ahead of print 2 December 2011

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Strain tensor analysis plays an essential role in geophysics and engineering applications since it provides a numerical measure on the relative deformation behavior of the object under investigation. A strain tensor can be estimated by observing the positional coordinates of the deforming network at different epochs. Consequently, the quality of a strain analysis is highly dependent on the accuracy of position measurement and network configuration. In this study, a strain sensitivity index, namely the minimum detectable principal strain parameter, has been developed based on the concept of the invariant function and statistical theory. A simulation test and a real case study have both been carried out to demonstrate the feasibility of the proposed approach. Based on the numerical results from the case study on the first‐order Global Positioning System (GPS) network in Taiwan, it has been revealed that the coastal areas in Taiwan have a lower capability in detecting surface strains due to a poor network configuration. On the other hand, it has also been illustrated that, by incorporating the network optimization guidelines developed in this study, the strain sensitivity index can be substantially improved in these areas.

Accuracy Evaluation of Terrestrial LiDAR and Multibeam Sonar Systems Mounted on a Survey Vessel

Michael Dix, Amr Abd‐Elrahman, Bon Dewitt, and Lou Nash

Journal of Surveying Engineering doi:http://dx.doi.org/10.1061/(ASCE)SU.1943-5428.0000075

Posted ahead of print 2 December 2011

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This research provides a performance test of terrestrial Light Detection and Ranging (LiDAR) and Multibeam Echo Sounder (MBES) scanners integrated with Global Navigation Satellite System/Inertial Navigation System (GNSS/INS) 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. Standard deviation, Root Mean Squared Error (RMSE), and mean were computed across all data sets for each experiment. Horizontal RMSE values of 0.06m and 0.03m were achieved for the LiDAR and sonar data, respectively. Vertical RMSE results of 0.04m 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.

To Level or Not to Level: Laser Scanner Inclination Sensor Stability and Application

Evon P. Silvia and Michael J. Olsen

Journal of Surveying Engineering doi:http://dx.doi.org/10.1061/(ASCE)SU.1943-5428.0000072

Posted ahead of print 19 November 2011

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Many modern terrestrial laser scanners (TLSs) are equipped with inclination/tilt sensors—also referred to as level compensators—that can correct out‐of‐level imperfections in an instrument setup. Some users elect to disable the inclination sensor when their scanner is equipped with one. Those who do use an inclination sensor may override its leveling data by linking to external control that defines the level plane. Our case study has shown that inclination sensor data can be a valuable quality check for the control data and overall point cloud alignment. Quality inclination sensor data requires careful scan planning. Specifically, lab tests indicate that scanner rotation speed influences the reliability of inclination sensor readings recorded during rotation. These inertial effects can be cancelled to a limited extent by measuring during both clockwise and counter‐clockwise rotations. A scan duration within a “stability threshold” can also minimize the inertial effects and variability in inclination sensor readings for scanners continuously measuring inclination data during rotation. Finally, inclination sensor readings from a full 360° rotation are recommended to reduce systematic bias.
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