675 results for Conference paper, 2000

  • Irregular vector-agent based simulation for land-use modelling

    Hammam, Yasser; Moore, Antoni; Whigham, Peter A; Freeman, Claire (2004-11)

    Conference paper
    University of Otago

    Urban structures exhibit complex patterns made of heterogeneous and irregular objects. Few works in the computational urban modelling literature have considered and examined the real geometric boundary of the city’s objects. However, most of these works are driven by Cellular Automata (CA) as a spatial modelling vehicle. This model has had success, but also has its limitations regarding the study of urban dynamics in computer simulation. Extensive modification of CA or use of a different modelling paradigm should be considered. We argue here that, representational realism must be achieved in urban complexity. This paper is an attempt to fill this gap to address the rigid structure of CA: we present a novel technique called the “vector-agent based simulation”, which uses discrete irregular objects as an autonomous spatial entity beneath an agent modelling structure. Through computer simulation, this new technique has been applied to von Thunen’s theory of agricultural land use as a hypothetical environment for model verification. The findings demonstrate that our proposal can be a new paradigm for urban simulation

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  • Assessment of the performance of image fusion for the mapping of snow

    Sirguey, Pascal; Oltmer, Sven; Mathieu, Renaud (2007-12-06)

    Conference paper
    University of Otago

    The assessment of the performance of multi-resolution image fusion, or image sharpening methods, is difficult. In the context of binary classification of snow targets in mountainous terrain, fusion methods were applied to help achieve more accurate mapping. To quantify objectively the gain of information that can be attributed to an increase in spatial resolution, we investigate the Mean Euclidean Distance (MED) between the snowline obtained from the classification, and a reference snowline (or a ground truth line), as a relevant indicator to measure both the discrepancy between datasets at different spatial resolutions, and the accuracy of the mapping process. First, a theoretical approach based on aggregating detailed reference images from the Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) showed that the MED has a linear relationship with the pixel size that makes it suitable to assess images of different resolutions. Secondly, we tested the MED to snow maps obtained ‘with’ or ‘without’ applying a fusion method to the MODerate Resolution Imaging Spectroradiometer (MODIS). We demonstrated that the MED identified a significant value added, in terms of mapping accuracy, which can be attributed to the fusion process. When the fusion method was applied to four different images, the MED overall decreased by more than 30%. Finally, such a ‘feature based’ quality indicator can also be interpreted as a statistical assessment of the planimetric accuracy of natural pattern outlines.

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  • Tracing the impacts of global sourcing on local communities: a historical analysis of employment relations in Queensland’s beef processing sector

    Insch, Andrea (2005-11)

    Conference paper
    University of Otago

    By focusing on firm-specific drivers the literature on global sourcing overlooks many of the wider impacts on host communities. In particular, impacts on the dynamic employment relationship have consequences for local governments and workers as well as MNEs engaged in global sourcing. Using historical methods this paper analyses the development of Queensland’s beef processing sector to identify patterns in global sourcing behaviour and the impacts on employment relations in local communities. The evidence reveals a pattern of inward FDI motivated by MNEs’ resource seeking objectives encouraged by government incentives. Whereas early global sourcing practices were sporadic they became more strategic. Cost minimisation was the enduring driver of this MNE activity. This ethos tempered relations between meat workers and employers and limited the direct and indirect benefits associated with job creation in Queensland’s regional host communities.

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  • Generic vector-agents

    Hammam, Yasser; Moore, Antoni; Whigham, Peter A; Freeman, Claire (2005-11)

    Conference paper
    University of Otago

    The work reported here has been motivated by the need for a generic spatial model to overcome the limitations of Cellular Automata (CA) regarding the rigid square-cell structure and limited neighbourhood configurations. A novel approach for spatial modelling technique is developed: the “vector-agent” in which the individual entity is represented by their real geometric boundaries (which can change over time) beneath an agent modelling structure. We show in this paper how the theory behind CA and agents can be combined to produce a generic and dynamic agent based on the vector data structure. This new paradigm has extended capabilities over the Geographic Automata (Torrens and Benenson, 2005) in terms of CA disunity and the abstraction of non-fixed-objects. Through computer simulation, different techniques and algorithms have been derived achieving a high degree of representational realism for a variety of phenomena

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  • Rule extraction from spatial data using local learning techniques

    Woodford, Brendon J (2005-11)

    Conference paper
    University of Otago

    We are now in the fourth decade where techniques such as fuzzy systems, statistics, neural networks and machine learning have all been developed and more recently applied for the purpose of spatial data mining. However these methods act as global learning models and subsequently may not be able to learn the subtle nature of these types of data sets. Local learning models such as the Support Vector Machine (SVM) and a more recent method such as that proposed by (Gilardi 2002) address the problem of global versus local learning but fail to offer many solutions as to what underlying patterns may exist within the data set in order to better understand the data set. In this paper we propose the Evolving Fuzzy Neural Network (EFuNN) as a model for a local learning mechanism for the purpose of predicting rainfall within a region of Switzerland and also use this model to generate rules and then to visualise these rules that may help to describe any patterns that may exist within the data set.

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  • The storage and reconstruction of polygon boundaries using circles

    Moore, Antoni; Mason, Chris; Whigham, Peter A; Thompson-Fawcett, Michelle (2003-12)

    Conference paper
    University of Otago

    This paper investigates the accuracy of using circles to store polygon boundaries. Can a series of xy points be accurately replaced by a smaller array of variably-sized circles used in a non space filling sense to approximate to the edge of the polygon? Two measures were used to ascertain this, areal error and visual error. A vector dataset representing the island of Rarotonga was converted from boundary coordinates to circle storage using a Voronoi-based medial axis approach. Three parameters were altered to derive as many as 150 circle-based realisations – minimum allowed circle radius, degree of overlap allowed between circles and Douglas-Peucker algorithm threshold (the latter algorithm of line reduction was used to extract “important” points from the polygon and add them to the circle list as “zero-radius circles”). This presentation presents and analyses the areal error and visual error results for all realisations.

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  • A practical spatial data capture technique for human motion research

    Chong, Albert K; Croft, Hayden (2005-11)

    Conference paper
    University of Otago

    The paper discusses the evaluation of a video image-splitting device for human motion research. NuView, a commonly available device and a digital video camera (DV) were used to capture stereo-video footage of athletes in training. The device permits two distinct views (left and right perspective views) to enter a single lens DV. A single convergence control in the device allows users to obtain stereo view of near and far objects. The research involves the calibration of a customized system for optimum motion tracking accuracy. A stereo-digitizing photogrammetric technique was used to determine the accuracy of the system. The results show that system can achieve optimum spatial data accuracy of 15 mm at an object distance of 8 m. The different in the horizontal and vertical accuracies are similar to those obtained by conventional stereo-aerial photogrammetric technique, i.e. the horizontal component is approximately two times better than z component.

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  • Keep your eye on the ball: Local versus global statistics in sport visualisation

    Whigham, Peter A (2005-11)

    Conference paper
    University of Otago

    This paper describes several simple local space-time statistical measures that can be applied to data that describes ball position over space and time. The main aim is to show that global statistics of rugby union do not describe the most important aspects of team domination, and that other measures may be more meaningful in terms of understanding the overall patterns of play. This paper introduces several measures for describing these local statistics, and shows for one example that they reflect the dominance of one team even though this is not reflected in the half-time score. The main conclusion is that the most important local statistics maintain an explicit spatial representation, and that therefore global measures of behaviour, that have removed the spatial patterns of play, are not appropriate descriptors for rugby union.

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  • HD aerial video for coastal zone ecological mapping

    Chong, Albert K (2007-12-06)

    Conference paper
    University of Otago

    The paper discusses a recent test of using High Definition (HD) video camera to obtain aerial mapping images for coastal zone study. Real-Time GPS was used to capture the ground control. It was revealed that the vibration from the aircraft has an adverse effect on the video footage. Consequently, each video frame was deinterlaced to obtain the odd and even fields as sub-frames. Deinterlacing removes the effect of aircraft vibration; however the process reduces the video frame format size to a sub-frame size which is a half of the original format size. The video camera was calibrated at full format size so the image must be rebuilt to full format size in order to achieve the required spatial accuracy. Tests show that the stereo-digitized 3D coordinate of beach features is similar to still-frame digital images at the same flying height. Because videoing does not require precise exposure timing as in the case of still-frame photography, HD video has a vey important advantage over conventional still-frame aerial photography for aerial mapping.

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  • Parallel processes and situation awareness display design

    Moyle, Sam A (2005-11)

    Conference paper
    University of Otago

    In recent years there has been trend away from single sensor/single (SS/SI) indicator boards as the means by which overall understanding of current work-flow is expressed. Rather, computer screen based Supervisory Control And Data Acquisition (SCADA) systems are being modified to meet this need. This paper discusses a continuing experiment that compares existing SCADA design elements and those with simple display modification; display changes that facilitate decision making by improving overall Situation Awareness (SA).

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  • A rule language for modelling and monitoring social expectations in multi-agent systems

    Cranefield, Stephen (2006)

    Conference paper
    University of Otago

    The full text is available only from the related link (you must be a subscriber to the SpringerLink service).

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  • S-map – a new soil database for New Zealand

    Lilburne, Linda; Hewitt, Allan; Webb, Trevor H.; Carrick, Sam (2004)

    Conference paper
    Landcare Research

    Soil information in New Zealand comprises maps and databases of varying accuracy and platforms. A project has been initiated to bring together this soil information in S-map – a new multi-layer soil database with national coverage. An important difference is that S-map is designed as a digital product and is thus not constrained by cartographic requirements. Rather than generalising polygons for aesthetic reasons, the best available information is now used regardless of its scale of origin. Also climate and topography are no longer used as soil descriptors. Key goals are to capture the fundamental soil inputs required by pedotransfer functions, and to record knowledge of uncertainty. This will then act as a platform for fusion with other environmental layers for spatial modelling. S-map will contain data predominantly new to the existing national spatial soil database. Gaps will be filled and previous low-resolution data will be upgraded. The aim is to provide digital data layers of soil classes and attributes with resolution at least equivalent to 1:50 000. Work in the lowlands is proceeding using conventional soil survey techniques. In the uplands (where relief is sufficient to make effective use of the national 25-m resolution DEM) modelling approaches are used with the technique depending on data type and terrain. There are some enormous challenges in this work including nationwide soil correlation, devising a common structure for lowland (good information) and upland (little information) soils, providing information about soil variability and uncertainty, and developing a model-base of pedotransfer functions that can be easily updated. This paper describes our approach and progress in solving these challenges.

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  • Nitrous oxide emissions from grazed pastures

    Saggar, Surinder; Hedley, C. B.; Giltrap, Donna L.; Tate, Kevin; Lambie, S.; Li, Changsheng (2004)

    Conference paper
    Landcare Research

    Because of the high spatial and temporal variability of N2O fluxes a process-based modelling approach is required that quantifies N2O emissions at the field level more accurately than the very empirical IPCC default methodology. Such an approach is needed to extrapolate field measurements from a limited number of sites to regional and national scales with known levels of uncertainties. Here we present seasonal variations in N2O emissions from two dairy pastures with contrasting soils and from a sheep pasture, assess the ability of a modified DNDC model “NZ-DNDC” to simulate these emissions, and compare the N2O emissions from dairy- and sheep-grazed pastures using an empirical methodology recommended by the IPCC, currently used in preparing New Zealand’s annual N2O emission inventory from grazed pastures. Results of our studies suggest that i) N2O emissions are mainly produced by denitrification, ii) uneven deposition of excretal N in grazed pastures results in high spatial and temporal variability, iii) emissions are low during the dry season, high in winter and medium in spring, and iv) annual emissions from sheep-grazed pastures are only about one-third of those from dairy-grazed pastures. The overall comparisons of predicted and measured annual emissions indicate NZ-DNDC should be applicable to the simulation of N2O emissions from a range of grazed pastures. Our measurements and model estimates show Emission Factors (EFs) are different for dairy and sheep-grazed systems and suggest one EF for all, as used in the current inventory using the IPCC approach, will not give accurate emission estimates.

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  • Mitigating gaseous losses of nitrogen from pasture soil with urease and nitrification inhibitors

    Singh, J.; Saggar, S.; Bolan, Nanthi S. (2004)

    Conference paper
    Landcare Research

    Addition of nitrogen (N) to soil from various sources (i.e., animal excreta, farm effluents, synthetic fertilizers, crop residues and biological fixation), results in release of gaseous N such as nitrous oxide (N2O) and ammonia (NH3). In grazed pasture soils, mitigation options need to focus on limiting the loss of N directly from animal excreta, farm effluents and synthetic fertilizers, and the indirect loss caused by leaching and (NH3) volatilization. One such approach is the use of urease (UI) and nitrification inhibitors (NI). Urease inhibitors retard the hydrolysis of urea N in urea-based fertilizers and urine, thereby decreasing the concentration of ammonium (NH4+) in soil solution and the subsequent NH3 volatilization. Whereas NIs specifically retard the oxidation of NH4+ to nitrite (NO2-), thereby decreasing the concentration of nitrate (NO3-) and the subsequent leaching and denitrification. However, strategies to reduce emission of one gas may affect the emission of the other. Therefore, abatement strategies require simultaneous measurements of NH3 and N2O emissions. In a joint project, Massey University and Landcare Research are attempting various approaches for the abatement of gaseous N emissions. This paper reports the impacts of UI (N-(n-butyl) thiophosphoric triamide; Agrotain) and NI (Dicyandiamide; DCD) on the emissions of NH3 and N2O from urine and urea applied to intact pasture soil cores. Our results indicate that the addition of UI Agrotain delayed the onset and reduced NH3 emissions by 27% and 23% from urea and urine, respectively. Urease inhibitor also reduced N2O emissions significantly from urine. DCD applied at 25 kg/ha to urea in the presence and absence of UI Agrotain reduced the amount of N2O emissions by 68% and 74% respectively. However, DCD did not cause any significant change in NH3 emissions. Our results suggest that there is a considerable scope for reduction of N2O emissions by applying (DCD) both in the presence and absence of Agrotain.

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  • Soil carbon changes and uncertainties with New Zealand land-use change

    Tate, Kevin; Wilde, R. H.; Giltrap, David J.; Baisden, W. T.; Saggar, Surinder; Trustrum, Noel A.; Scott, N. A. (2004)

    Conference paper
    Landcare Research

    An IPCC-based Carbon Monitoring System (CMS) is being implemented to monitor soil C stocks and flows for New Zealand. Geo-referenced soil C data from 1153 sites (0.3 m depth) are used in the current version to assign steady-state soil C stocks to various combinations of soil class, climate, and land use. Overall, CMS estimates of soil C stock are consistent with detailed, stratified soil C measurements at specific sites and over larger regions. Soil C changes accompanying land-use changes were quantified using a national set of land-use effects (LUEs) derived using a General Linear Model. Predicted and measured soil C changes for the grazing–forestry conversion agreed closely. Most soil C is stored in grazing lands (1480±60 Tg to 0.3 m depth), which appear to be at or near steady state; their conversion to exotic forests and shrubland contributed most to the predicted national soil C loss of 0.7±0.3 Tg C yr-1 during 1990–2000. Major uncertainties arise from estimates of changes in the areas involved, the assumption that soil C is at steady state for all land-cover types, and from lack of soil C data for some LUEs. Other uncertainties in our current soil CMS include: spatially integrated annual changes in soil C for the major land-use changes; lack of soil-C-change estimates below 0.3 m; C losses from erosion; and the contribution of agricultural management of organic soils.

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