Infrastructure Engineering - Theses
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ItemGPS structural deformation monitoring: the mid-height problem( 2008)GPS has been used to monitor engineering structures for a number of reasons. One important reason for monitoring high rise buildings (and other engineering structures) is their safety assessment in events of extreme loading, such as earthquakes and storms. Decisions must be made as soon as possible, whether to allow re-occupation of such buildings, or to assess them for further damage. The time required to reach such decisions is cost-critical, both for the building owner or manager and for the agency doing the assessment. Peak inter-storey drift ratio and detection of permanent damage are some of the damage assessment parameters recommended by assessment agencies. Traditionally, accelerometers have been used to monitor these parameters. Accelerometers measure accelerations which are double-integrated to get displacements. These double integrated displacements are then used for computing the inter-storey drift ratios and locating permanent damage. Displacements obtained by double-integration and inter-storey drift ratios by subtraction of these displacements, are often erroneous and unreliable and direct measurement of displacement is preferred. Direct measurement of displacement is required at a number of points along the height of the building. For example, for computing inter-storey drift ratios, measurements of displacement at both the floor level and roof level are required. Such points on buildings and other engineering structures of vertical profile are termed as mid-height points in this thesis. While GPS has been used for deformation monitoring of engineering structures and to assist in damage assessment during and after extreme loading events, its use has been limited to roof top installations. This research is an attempt to measure displacements at mid-height locations of engineering structures of vertical profile using GPS. (For complete abstract open document).
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ItemSequential phased estimation of ionospheric path delays for improved ambiguity resolution over long GPS baselines( 2006-12)Satellite-based navigation systems make it possible to determine the relative positions of points on the earth with centimetre or even millimetre level accuracy over baselines of up to several thousand kilometres. The highest possible accuracy can only be achieved if the carrier phase integer ambiguities can be resolved. In order to resolve the L1 and L2 integer ambiguities over long GPS baselines, the double difference residual ionospheric errors must be estimated for every satellite, every epoch. The resulting number of parameters is usually too large for estimation using ordinary least squares to be practical due to the time or computing resources needed for the processing. The technique currently used to efficiently estimate the parameters is known as pre-elimination. Pre-elimination divides the unknowns into parameters of interest (the coordinates and ambiguities) and nuisance parameters (the ionospheric path delays). The nuisance parameters are treated as stochastic variables and modelled as process noise, avoiding the need for them to be explicitly estimated. Whilst this approach is highly efficient, it makes assumptions about the stochastic behaviour of the residual ionospheric error that are not necessarily valid. The effectiveness of preelimination can be increased through the use of a deterministic model of the ionosphere. It is the hypothesis of this research that the ionospheric error can be more effectively estimated than is possible with pre-elimination, leading to more reliable ambiguity resolution for long baseline precise positioning. (For complete abstract open document)
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ItemA multi-purpose cadastre prototype on the web( 2000-08)The Multi-Purpose Cadastre concept has been discussed over the last three decades. The concept, although idealistic when conceived, is still regarded as visionary in addressing the inherent limitations of most modern geo-spatial systems, especially cadastral systems worldwide. The concept is being used to better disseminate and utilise the increasingly large amount of data contained in many of the geo-spatial databases developed over the last few years. The utilisation of the World Wide Web has allowed these geo-spatial systems to evolve into online ‘virtual’ systems that are accessible by most people with the appropriate tools (the computers and telephone lines). This thesis analysed the growing development of these online systems. It describes a review of online cadastral systems that revealed the similarities in moving towards the future vision of cadastral systems of the 21st century, as highlighted by the International Federation of Surveyors document, Cadastre 2014. The rapidly growing volume of geo-spatial data, which has been attributed by technologies such as remote sensing and Global Positioning Systems, are impacting on the way societies of today, are using, viewing and storing geo-spatial data. Improvements in related areas such as the Spatial Data Infrastructure, the Open GIS Consortium and the Australian World Wide Web Mapping Consortium are described and discussed in this thesis.