Gethin Wyn Roberts

Global Positioning System aided autonomous construction plant control and guidance

The advent of Real Time Kinematic (RTK) Global Positioning System (GPS) positioning means that this technology can now be used for dynamic control and guidance applications. The paper outlines the recent advances in GPS technology, which have enabled RTK GPS to become a reality. Tests have been carried out in construction plant control and monitoring applications with a demonstrated precision of the order of a few millimeters. The results are compared with those achieved using a laser level and a digital automatic level.

A review of the use of terrestrial laser scanning application for change detection and deformation monitoring of structures

Change detection and deformation monitoring is an active area of research within the field of engineering surveying and other overlapping areas such as structural and civil engineering. This paper reviews the application of terrestrial laser scanning in the monitoring of structures and discusses registration and georeferencing of scan data. Past terrestrial laser scanning research work has shown trends in addressing issues such as accurate registration and georeferencing of scans, error modelling, point cloud processing techniques for deformation analysis, scanner calibration and detection of millimetre deformations. However, several issues are still open to investigation such as robust methods of point cloud processing for detecting change and deformation, incorporation of measurement geometry in deformation measurements, design of data acquisition and quality assessment for precise measurements and modelling the environmental effects on the performance of laser scanning. A three-stage process model for deformation analysis is proposed as conceptualised from the material reviewed.

GPS monitoring of a steel box girder viaduct

Structural performance monitoring of bridges has increased as major infrastructure ages and is required to sustain loads that are significantly greater than those predicted during design. Structural stiffness and/or mass distribution can change over the lifespan of a bridge structure. Resulting changes in profile or resonant frequency provide key indicators of change, and may identify structural defects. Field tests using GPS for monitoring relatively small deformations were carried out on a steel box girder viaduct bridge in the UK. The configuration consisted of five GPS receivers located at key locations on the viaduct and two reference GPS receivers. GPS data was collected at either 10 Hz or 20 Hz and post-processed using proprietary software, along with appropriate filtering and spectral analysis. Three main frequencies were clearly detected by the GPS in the vertical component. A previously reported frequency of approximately 0.56 Hz was identified along with two other frequencies. The peak vertical deflections lie in the range of ± 50 mm, while lateral and longitudinal deflections of much smaller magnitude – in the order of a few mm – are also measured. The use of GPS leads to readily obtained and useful engineering data for continued monitoring of structures.

Experimental results of Locata: A high accuracy indoor positioning system

Accurate indoor positioning is required for a variety of commercial applications, including warehouse automation, asset tracking, emergency first-responders, and others. In fact, the general expectation of users today is for ℌGPS-likeℍ positioning performance anywhere they go. The inherent limitations of GPS signal availability indoors and in satellite-occluded environments, however, has forced researchers to investigate alternative technologies which may be able to replicate GPS/GNSS performance indoors. A new terrestrial RF-based distance measurement technology, trademarked ℌLocataℍ, has overcome the technical challenges required to create ℌa localised autonomous terrestrial replica of GNSSℍ. Signals from the Locata network are seen by receiver devices as equivalent to (but totally independent from) the GNSS satellite constellation(s). This technical paper describes indoor positioning results with the latest generation of Locata positioning devices. The results demonstrate that Locatas technology enables cm-level positioning in severe multipath environments where conventional high-accuracy radiopositioning has previously been impossible.

The Integration of GPS and Pseudolites for Bridge Monitoring

One application in structural engineering is measuring the movement of suspension bridges. Under unfavourable wind conditions or heavy traffic loads cable suspension bridges may move up to a few metres. Therefore, a positioning system used to monitor bridge movements can provide extremely valuable information. For such monitoring applications it is desirable for the positioning system to deliver equal precision in all position components, all the time.

A Tale of Five Bridges; the use of GNSS for Monitoring the Deflections of Bridges

Abstract The first Bridge Monitoring surveying was carried out in 1996 by the authors, through attaching Ashtech ZXII GPS receivers onto the Humber Bridge’ parapet, and gathering and further analysing the resulting 1 Hz RTK GPS data. Various surveys have subsequently been conducted on the Humber Bridge, the Millennium Bridge, the Forth Road Bridge, the Severn Suspension Bridge and the Avonmouth Viaduct. These were all carried out using survey grade carrier phase/pseudorange GPS and later GNSS receivers. These receivers were primarily dual frequency receivers, but the work has also investigated the use of single frequency receivers, gathering data at 1 Hz, 10 Hz, 20 Hz and even 100 Hz. Various aspects of the research conducted are reported here, as well as the historical approach. Conclusions are shown in the paper, as well as lessons learnt during the development of this work. The results are compared to various models that exist of the bridges’ movements, and compare well. The results also illustrate that calculating the frequencies of the movements, as well as looking at the magnitudes of the movements, is an important aspect of this work. It is also shown that in instances where the magnitudes of the movements of the bridge under investigation are small, it is still possible to derive very accurate frequencies of the movements, in comparison to the existing models.

Measurement Signal Quality Assessment on All Available and New Signals of Multi-GNSS (GPS, GLONASS, Galileo, BDS, and QZSS) with Real Data

Global Navigation Satellite Systems (GNSS) Carrier Phase (CP)-based high-precision positioning techniques have been widely used in geodesy, attitude determination, engineering survey and agricultural applications. With the modernisation of GNSS, multi-constellation and multi-frequency data processing is one of the foci of current GNSS research. The GNSS development authorities have better designs for the new signals, which are aimed for fast acquisition for civil users, less susceptible to interference and multipath, and having lower measurement noise. However, how good are the new signals in practice? The aim of this paper is to provide an early assessment of the newly available signals as well as assessment of the other currently available signals. The signal quality of the multi-GNSS (GPS, GLONASS, Galileo, BDS and QZSS) is assessed by looking at their zero-baseline Double Difference (DD) CP residuals. The impacts of multi-GNSS multi-frequency signals on single-epoch positioning are investigated in terms of accuracy, precision and fixed solution availability with known short baselines.

Evaluating the performance of low cost MEMS inertial sensors for seamless indoor/outdoor navigation

For all mobile, location based applications, location availability (either on demand or continuously) is the primary performance requirement of the positioning technologies used. In most cases, this requirement outweighs that of meeting a specified accuracy, as the granularity of information provided to the user can be scaled around the computed positioning accuracy. What is therefore important is being able to generate a position solution and its accuracy at a specified level of confidence. For these applications, meeting the requirement of 100% availability is a significant challenge for individual positioning technologies, even more so when navigating between indoor and outdoor environments. Whilst operating under ideal operating conditions, GPS provides excellent positioning coverage. In indoor environments, position solutions can be generated using infrastructure based technologies such as RFiD and WiFi or augmentation sensors such as inertial navigation systems. Micro- Electromechanical Sensor (MEMS) inertial sensors are a popular option as they offer an autonomous capability that can potentially augment performance seamlessly across indoor and outdoor environments with marginal cost implications. This paper presents the results of a practical test undertaken to evaluate the performance of commercially available MEMS inertial sensors. In particular, results obtained that characterize the performance of these sensors against GPS in the transition zone between indoor and outdoor environments will be presented.

Monitoring the height deflections of the Humber Bridge by GPS, GLONASS, and finite element modelling

The following paper details trials recently conducted by the IESSG whereby kinematic GPS and the Russian equivalent to GPS, Global’naya Navigatsionnaya Sputnikovaya Sistema (GLONASS), were used to monitor the deflection of the Humber Bridge under a loading of 160 tons, moved across the bridge by five articulated lorries. The trial consisted of placing four dual frequency GPS receivers and a GPS/GLONASS receiver on the bridge deck, a dual frequency GPS receiver upon one of the lorries and reference receivers placed on land. The data, gathered at 5 Hz, was then processed in an On the Fly manner resulting in a precision of the order of a few millimetres. Finite element modelling of such structures can take advantage of similar trials and results. The results were compared to a finite element model by the Department of Mechanical Engineering at Brunel University, and showed remarkable comparisons.

On the improvements of the single point positioning accuracy with Locata technology

This work focuses on the performances of Locata technology in single point positioning using different firmware versions (v2.0 and v4.2). The main difference is that the Locata transmitters with firmware v2.0 are single frequency, whereas in the v4.2, they are dual frequency. The performance of the different firmware versions has been measured in different environments including an urban canyon-like environment and a more open environment on the roof of the Nottingham Geospatial Building. The results obtained with firmware v4.2 show that with more available signals, cycle slips can be more easily detected, together with the improvement of the detection of multipath fading on the received signal. As a result, the noise level on the carrier phase measurements recorded with firmware v4.2 is equal on average to a third of the level of noise on the measurements recorded with firmware v2.0. In addition, with either firmware, the accuracy of the position is at the sub-centimeter level on the East and North coordinates. The Up coordinate accuracy is generally less accurate and more sensitive to the geometry of the network in our experiments. We then show the importance of the geometry of the Locata network on the accuracy of Locata positioning system through the demonstration of the relationship between the dilution of precision value and the confidence ellipse. We also demonstrate that the model of the noise on the Locata coordinates is a white Gaussian noise with the help of the autocorrelation function. To some extent, this technique can help to detect whether the Wi-Fi technology is interfering with the Locata technology and degrades the positioning accuracy.