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Moradi, Mohammad Mehdi. "Spatial and spatio-temporal point patterns on linear networks." Doctoral thesis, Universitat Jaume I, 2018. http://hdl.handle.net/10803/664140.
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A thesis submitted in partial fulfillment of the requirements for the degree of Doctor in Information Management, specialization in Geographic Information Systems<br>The last decade witnessed an extraordinary increase in interest in the analysis
of network related data and trajectories. This pervasive interest is partly caused
by a strongly expanded availability of such datasets. In the spatial statistics field,
there are numerous real examples such as the locations of traffic accidents and
geo-coded locations of crimes in the streets of cities that need to restrict the
support of the underlying process over such linear networks to set and define a
more realistic scenario. Examples of trajectories are the path taken by moving
objects such as taxis, human beings, animals, etc.
Intensity estimation on a network of lines, such as a road network, seems to
be a surprisingly complicated task. Several techniques published in the literature,
in geography and computer science, have turned out to be erroneous. We
propose several adaptive and non-adaptive intensity estimators, based on kernel
smoothing and Voronoi tessellation. Theoretical properties such as bias, variance,
asymptotics, bandwidth selection, variance estimation, relative risk estimation,
and adaptive smoothing are discussed. Moreover, their statistical performance is
studied through simulation studies and is compared with existing methods.
Adding the temporal component, we also consider spatio-temporal point patterns
with spatial locations restricted to a linear network. We present a nonparametric
kernel-based intensity estimator and develop second-order characteristics
of spatio-temporal point processes on linear networks such as K-function
and pair correlation function to analyse the type of interaction between points.
In terms of trajectories, we introduce the R package trajectories that contains
different classes and methods to handle, summarise and analyse trajectory data.
Simulation and model fitting, intensity estimation, distance analysis, movement
smoothing, Chi maps and second-order summary statistics are discussed. Moreover, we analyse different real datasets such as a crime data from Chicago
(US), anti-social behaviour in Castell´on (Spain), traffic accidents in Medell´ın
(Colombia), traffic accidents in Western Australia, motor vehicle traffic accidents
in an area of Houston (US), locations of pine saplings in a Finnish forest, traffic
accidents in Eastbourne (UK) and one week taxi movements in Beijing (China).
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Wilson, Helen Elizabeth. "Statistical analysis of replicated spatial point patterns." Thesis, Lancaster University, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.268009.
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The field of pathology provides us with many opportunities for collecting replicated spatial data. Using an ordinary microscope, for example, we can digitise cell positions within windows imposed on pieces of tissue. Suppose now that we have some such replicated spatial data from several groups of individuals, where each point in each window represents a cell position. We seek to determine whether the spatial arrangement of cells differs between the groups. We propose and develop a new method which allows us to answer such questions, and apply it to some spatial neuro-anatomical data. We introduce point process theory, and extend the existing second order methods to deal with replicated spatial data. We conclude the first part of the thesis by defining Sudden Infant Death Syndrome (S.LD.S.) and Intra-Uterine Growth Retardation (LU.G.R.), and stating why these conditions are neuro-anato,mically interesting. We develop and validate a method for comparing groups of spatial data, which is motivated by analysis of variance, and uses a Monte Carlo procedure to attach significance to between-group differences. Having carried out our initial investigative work looking exclusively at the one-way set up, we extend the new methods to cope with two and higher way set ups, and again carry out some validation. We turn our attention to practical issues which arise in the collection of spatial neuroanatomical data. How, for example, should we collect the data to ensure the unbiasedness of any inference we may draw from it? We introduce the field of stereology which facilitates the unbiased sampling of tissue. We note a recent proposal to assess spatial distribution of cells using a stereological approach, and compare it with an existing second order method. We also note the level of structural heterogeneity within the brain, and consider the best way to design a sampling protocol. We conclude with a spatial analysis of cell position data, collected using our specified design, from normal birth-weight non S.LD.S., normal birth-weight S.I.D.S and low birth-weight S.LD.S cases.
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Doguwa, S. I. "Statistical analysis of mapped spatial point patterns." Thesis, University of Essex, 1988. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.383379.
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González, Monsalve Jonatan A. "Statistical tests for comparisons of spatial and spatio-temporal point patterns." Doctoral thesis, Universitat Jaume I, 2018. http://hdl.handle.net/10803/462034.
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We mainly introduce a new set of tests to compare functional descriptors in point processes context. Firstly, since the study of spatio-temporal point processes has not been widely covered in the literature, a complete review is made. The review is a reference paper of the available techniques and approaches regarding the spatio-temporal context. Secondly, a studentized permutation test is developed in the spatio-temporal case. This test is motivated by locations of tornadoes in the U.S. in a period of 36 years. Some tools have been developed as a non-separable estimator of the first-order intensity, which allows a realistic analysis of the phenomenon through the new test.
Finally, a factorial two-way design is considered, where the observations are spatial point patterns in presence of replication. This methodology is motivated by a minerals engineering experiment. We develop statistics to test the influence of the factors and the possible interaction effects.<br>Desarrollamos un nuevo conjunto de pruebas para comparar descriptores funcionales en el contexto de procesos puntuales. Puesto que el estudio de los procesos puntuales espacio-temporales no ha sido muy exhaustivo en la literatura, hemos hecho un artículo de resumen. Introducimos un test de permutación para grupos de patrones puntuales espacio-temporales motivado por las ubicaciones de ocurrencias de tornados en EE.UU. durante 36 años. Hemos desarrollado algunas técnicas como la estimación de la intensidad de primer-orden sin suponer separabilidad, lo que permite un tratamiento más realista del fenómeno climático en sí mismo a través del nuevo test.Finalmente, hemos desarrollado algunas técnicas para el análisis de la varianza de experimentos de dos factores en presencia de réplicas cuando las observaciones son patrones puntuales espaciales. Esta metodología está motivada por un experimento de ingeniería de minerales. Desarrollamos algunos estadísticos adecuados para probar la influencia de los factores y su posible interacción.
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Pereira, Sandra M. C. "Analysis of spatial point patterns using hierarchical clustering algorithms." University of Western Australia. School of Mathematics and Statistics, 2003. http://theses.library.uwa.edu.au/adt-WU2004.0056.
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[Formulae and special characters can only be approximated here. Please see the pdf version of the abstract for an accurate reproduction.] This thesis is a new proposal for analysing spatial point patterns in spatial statistics using the outputs of popular techniques of (classical, non-spatial, multivariate) cluster analysis. The outputs of a chosen hierarchical algorithm, named fusion distances, are applied to investigate important spatial characteristics of a given point pattern. The fusion distances may be regarded as a missing link between the fields of spatial statistics and multivariate cluster analysis. Up to now, these two fields have remained rather separate because of fundamental differences in approach. It is shown that fusion distances are very good at discriminating different types of spatial point patterns. A detailed study on the power of the Monte Carlo test under the null hypothesis of Complete Spatial Randomness (the benchmark of spatial statistics) against chosen alternative models is also conducted. For instance, the test (based on the fusion distance) is very powerful for some arbitrary values of the parameters of the alternative. A new general approach is developed for analysing a given point pattern using several graphical techniques for exploratory data analysis and inference. The new strategy is applied to univariate and multivariate point patterns. A new extension of a popular strategy in spatial statistics, named the analysis of the local configuration, is also developed. This new extension uses the fusion distances, and analyses a localised neighbourhood of a given point of the point pattern. New spatial summary function and statistics, named the fusion distance function H(t), area statistic A, statistic S, and spatial Rg index, are introduced, and proven to be useful tools for identifying relevant features of spatial point patterns. In conclusion, the new methodology using the outputs of hierarchical clustering algorithms can be considered as an essential complement to the existing approaches in spatial statistics literature.
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Liu, Jie. "Exploring Ways of Identifying Outliers in Spatial Point Patterns." Digital Commons @ East Tennessee State University, 2015. https://dc.etsu.edu/etd/2528.
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This work discusses alternative methods to detect outliers in spatial point patterns.
Outliers are defined based on location only and also with respect to associated variables. Throughout the thesis we discuss five case studies, three of them come from experiments with spiders and bees, and the other two are data from earthquakes in a certain region. One of the main conclusions is that when detecting outliers from the point of view of location we need to take into consideration both the degree of clustering of the events and the context of the study. When detecting outliers from the point of view of an associated variable, outliers can be identified from a global or local perspective. For global outliers, one of the main questions addressed is whether the outliers tend to be clustered or randomly distributed in the region. All the work was done using the R programming language.
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Soale, Abdul-Nasah. "Spatio-Temporal Analysis of Point Patterns." Digital Commons @ East Tennessee State University, 2016. https://dc.etsu.edu/etd/3120.
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In this thesis, the basic tools of spatial statistics and time series analysis are applied to the case study of the earthquakes in a certain geographical region and time frame. Then some of the existing methods for joint analysis of time and space are described and applied. Finally, additional research questions about the spatial-temporal distribution of the earthquakes are posed and explored using statistical plots and models. The focus in the last section is in the relationship between number of events per year and maximum magnitude and its effect on how clustered the spatial distribution is and the relationship between distances in time and space in between consecutive events as well as the distribution of the distances.
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Pranchai, Aor. "Spatial patterns and processes in a regenerating mangrove forest." Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2015. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-171569.
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The global effort to rehabilitate and restore destroyed mangrove forests is unable to keep up with the high mangrove deforestation rates which exceed the average pace of global deforestation by three to five times. Our knowledge of the underlying processes of mangrove forest regeneration is too limited in order to find suitable techniques for the restoration of degraded mangrove areas. The general objective of my dissertation was to improve mangrove restoration by understanding regeneration processes and local plant-plant interaction in a regenerating Avicennia germinans forest.
The study was conducted in a high-shore mangrove forest area on the Ajuruteua peninsula, State of Para, Northern Brazil. The dwarf forest consisting of shrub-like trees is recovering from a stand-replacing event caused by a road construction in 1974 which interrupted the tidal inundation of the study area. Consequently, infrequent inundation and high porewater salinity limit tree growth and canopy closure.
All trees and seedlings were stem-mapped in six 20 m x 20 m plots which were located along a tree density gradient. Moreover, height, crown extent, basal stem diameter of trees were measured. The area of herbaceous ground vegetation and wood debris were mapped as well. The mapped spatial distribution of trees, seedlings and covariates was studied using point pattern analysis and point process models, such as Gibbs and Thomas point process, in order to infer underlying ecological processes, such as seed dispersal, seedling establishment, tree recruitment and tree interaction.
In the first study (chapter 2), I analyzed the influence of abiotic and biotic factors on the seedling establishment and tree recruitment of A. germinans during the recolonization of severely degraded mangrove sites using point process modeling. Most seedlings established adjacent to adult trees especially under their crown cover. Moreover, seedling density was higher within patches of the herbaceous salt-marsh plants Blutaparon portulacoides and Sesuvium portulacastrum than in uncovered areas. The higher density of recruited A. germinans trees in herb patches indicated that ground vegetation did not negatively influence tree development of A. germinans. In addition, tree recruitment occurred in clusters. Coarse wood debris had no apparent effect on either life stage. These results confirm that salt-marsh vegetation acts as the starting point for mangrove recolonization and indicate that the positive interaction among trees accelerates forest regeneration.
In the second study (chapter 3), I analyzed how intraspecific interaction among A. germinans trees determines their growth and size under harsh environmental conditions. Interaction among a higher number of neighboring trees was positively related to the development of a focal tree. However, tree height, internode length and basal stem diameter were only positively associated in low-density forest stands (1.2 trees m-2) and not in forest stands of higher tree density (2.7 trees m-2). These results indicated a shift from facilitation, i.e. a positive effect of tree interaction, towards a balance between facilitation and competition.
In the third study (chapter 4), I used point process modeling and the individual-based model mesoFON to disentangle the impact of regeneration and interaction processes on the spatial distribution of seedlings and trees. In this infrequently inundated area, propagules of A. germinans are only dispersed at a maximum distance of 3 m from their parent tree. Furthermore, there is no evidence that the following seedling establishment is influenced by trees. I was able to differentiate positive and negative tree interactions simulated by the mangrove model mesoFON regardless of dispersal processes based on static tree size information using the mark-correlation function.
The results of this dissertation suggest that mangrove forest regeneration in degraded areas is a result of facilitative and not competitive interactions among mangrove trees, seedling and herbaceous vegetation. This has important implications for the restoration of degraded mangrove forest. Degraded mangrove areas are usually restored by planting a high number of evenly spaced seedlings. However, high costs constrain this approach to small areas. Assisting natural regeneration could be a less costly alternative. Herbaceous vegetation plays a crucial role in forest recolonization by entrapping propagules and possibly ameliorating harsh environmental conditions. So far only competition among mangrove trees has been considered during restoration. However, facilitative tree interactions could be utilized by planting seedling clusters in order to assist natural regeneration instead of planting seedlings evenly-spaced over large areas.
This dissertation also showed that point pattern analysis and point process modeling can enable forest ecologists to describe the spatial distribution of trees as well as to infer underlying ecological processes.
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Packard, Kevin Carew. "Modeling spatial patterns of mixed-species Appalachian forests with Gibbs point processes." Diss., Virginia Tech, 2009. http://hdl.handle.net/10919/37385.
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Stochastic point processes and associated methodology provide a means for the statistical analysis and modeling of the spatial point pattern formed from forest tree stem locations. Stochastic Gibbs point processes were explored as models that could simulate short-range clustering arising from reproduction of trees by stump sprouting, and intermediate-range inhibition of trees that may result from competition for light and growing space. This study developed and compared three pairwise interaction processes with parametric models for 2nd-order potentials and three triplets processes with models for 2nd- and 3rd-order potentials applied to a mixed-species hardwood forest in the Southern Appalachian Mountains of western North Carolina. Although the 2nd-order potentials of both the pairwise interaction and triplets processes were allowed to be purely or partially attractive, the proposed Gibbs point process models were demonstrated to be locally stable. The proposed Gibbs point processes were simulated using Markov Chain Monte Carlo (MCMC) methods; in particular, a reversible-jump Metropolis-Hastings algorithm with birth, death, and shift proposals was utilized. Parameters for the models were estimated by a Bayesian inferential procedure that utilizes MCMC methods to draw samples from the Gibbs posterior density. Two Metropolis-Hastings algorithms that do this sampling were compared; one that estimated ratios of intractable normalizing constants of the Gibbs likelihood by importance sampling and another that introduced an auxiliary variable to cancel the normalizing constants with those in the auxiliary variableâ s proposal distribution.
Results from this research indicated that attractive pairwise interaction models easily degenerate into excessively clustered patterns, whereas triplets processes with attractive 2nd-order and repulsive 3rd-order interactions are more robust against excessive clustering. Bayesian inference for the proposed triplets models was found to be very computationally expensive. Slow mixing of both algorithms used for the inference combined with the long iteration times limited the practicality of the Bayesian approach. However the results obtained here indicate that triplets processes can be used to draw inference for and simulate patterns of mixed-species Appalachian hardwood forests.<br>Ph. D.
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Stanford, Derek C. "Fast automatic unsupervised image segmentation and curve detection in spatial point patterns /." Thesis, Connect to this title online; UW restricted, 1999. http://hdl.handle.net/1773/8976.
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Brown, Calum. "Spatial patterns and species coexistence : using spatial statistics to identify underlying ecological processes in plant communities." Thesis, University of St Andrews, 2012. http://hdl.handle.net/10023/3084.
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The use of spatial statistics to investigate ecological processes in plant communities is becoming increasingly widespread. In diverse communities such as tropical rainforests, analysis of spatial structure may help to unravel the various processes that act and interact to maintain high levels of diversity. In particular, a number of contrasting mechanisms have been suggested to explain species coexistence, and these differ greatly in their practical implications for the ecology and conservation of tropical forests. Traditional first-order measures of community structure have proved unable to distinguish these mechanisms in practice, but statistics that describe spatial structure may be able to do so. This is of great interest and relevance as spatially explicit data become available for a range of ecological communities and analysis methods for these data become more accessible. This thesis investigates the potential for inference about underlying ecological processes in plant communities using spatial statistics. Current methodologies for spatial analysis are reviewed and extended, and are used to characterise the spatial signals of the principal theorised mechanisms of coexistence. The sensitivity of a range of spatial statistics to these signals is assessed, and the strength of such signals in natural communities is investigated. The spatial signals of the processes considered here are found to be strong and robust to modelled stochastic variation. Several new and existing spatial statistics are found to be sensitive to these signals, and offer great promise for inference about underlying processes from empirical data. The relative strengths of particular processes are found to vary between natural communities, with any one theory being insufficient to explain observed patterns. This thesis extends both understanding of species coexistence in diverse plant communities and the methodology for assessing underlying process in particular cases. It demonstrates that the potential of spatial statistics in ecology is great and largely unexplored.
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Brandenberg, Kristin. "Point of view : How printed patterns evolve through perspective." Thesis, Högskolan i Borås, Akademin för textil, teknik och ekonomi, 2017. http://urn.kb.se/resolve?urn=urn:nbn:se:hb:diva-12395.
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’Point of view’ is an investigation of changeable surface patterns in the textile design field. The investigation is performed in order to get a deeper understanding of the relationship between changeable surface patterns and three-dimensional contexts to explore alternative methods. The aim is to design surface patterns in a three dimensional context developed through printing and layering techniques, and to explore how the patterns change depending on the observer’s perspective. Practice based design experiments were carried out to explore materials and printing techniques such as transfer, digital and burn out. The patterns were in turn placed on a cubic frame with inner and outer layers, and studied for their effects on one another. The project resulted in a series of surface patterns that were applied in a spatial context. The findings propose an alternative method for designing changeable surface patterns in a three-dimensional setting, using layers, transparency and distance as factors.
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Haltigin, Timothy William. "Interpreting polygonal terrain network arrangements on Earth and Mars using spatial point patterns." Thesis, McGill University, 2010. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=92211.
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Polygonal terrain is one of the most common landforms found throughout the periglacial environments of Earth and Mars. These networks of interconnected trough-like features form through a complex interaction of climatological and rheological processes and often signify the presence of ground ice deposits.<br>Previous comparisons of morphological similarities amongst sites on both planets have typically relied upon qualitative techniques. In some cases, limited quantitative metrics have been utilized, but there remains no objective, repeatable method by which to compare terrestrial and Martian polygonal terrain.<br>The overarching goal of this work is to assess the utility of a particular statistical method Spatial Point Pattern Analysis (SPPA) for analyzing polygonal network geometries at sites on Earth and Mars. Based around four sets of experimental results, the objectives addressed by this thesis are to:<br>(i) demonstrate that SPPA is an effective means by which qualitative, observable variations in polygonal morphology can be quantified;<br>(ii) examine the effects of different input data collection methods on the output of the statistical model;<br>(iii) establish that the analytical results of SPPA as applied to polygonal terrain are rooted in terrestrial geomorphic theory, and;<br>(iv) perform a case study in which SPPA is used to reconstruct the landscape history of a particular region of Mars.<br>Our results show that SPPA successfully differentiates between the geometric patterns observed at various sites, simultaneously providing data pertaining to the cumulative distribution of trough segment lengths and the overall network arrangement. In providing guidelines for future applications of this technique, we demonstrate that SPPA results are the most reliable when using data derived from ground-based terrain surveys or GIS-based analysis of high-resolution (< 0.5m/pixel) satellite or aerial images. Moreover, extensive fieldwork in the Canadian High Arctic illustrates that the observed point pattern of a given site is linked to its substrate composition and relative stage of development. Finally, using the field results as an analogical source to inform the interpretation of Martian geomorphic processes, a landscape evolution model is proposed to explain the development of a poorly-understood landform (scalloped depressions) in the ice-rich terrains of the Martian northern latitudes.<br>Les formes de terrain polygonales sont parmi les plus communes dans les environnements périglaciaires sur la Terre comme sur Mars. Ces réseaux de dépressions interconnectées sont issus d'interactions complexes entre des processus climatologiques et rhéologiques et indiquent souvent la présence de dépôts de glace souterraine.<br>Les comparaisons précédentes sur les similarités morphologiques entre des sites à la surface des deux planètes ont souvent été basées sur des techniques qualitatives. Dans certains cas, quelques mesures quantitatives ont été utilisées, mais il n'y avait aucune méthode objective qui permettait de comparer les formes de terrain polygonales terrestres et martiennes.<br>L'objectif général de cette recherche est d'évaluer l'utilité d'une méthode statistique particulière l'analyse de patrons spatiaux ponctuels (APSP) pour analyser la géométrie des réseaux polygonaux sur Terre et sur Mars. À partir de quatre séries de données expérimentales, les objectifs spécifiques de cette thèse sont:<br>(i) de démontrer que l'APSP est une méthode efficace par laquelle les variations observées de façon qualitative dans la morphologie des polygons peuvent être quantifiées;<br>(ii) d'examiner les effets de différentes méthodes de cueillette de données à l'entrée sur les résultats du modèle statistique;<br>(iii) d'établir que les résultats analytiques de l'APSP appliqués à un terrain polygonal ont comme fondement théorique les concepts géomorphologiques terrestres;<br>(iv) de réaliser une étude de cas qui utilise l'APSP afin de reconstruire l'histoire du paysage dans une région spécifique de Mars.<br>Nos résultats indiquent que l'APSP permet de différencier avec succès les patrons géométriques observés à différents sites, tout en procurant des données pertinentes sur la distribution cumulative des longueurs de segments de dépression et sur l'agencement général de ces réseaux. En fournissant des directives pour les applications futures de cette technique, nous démontrons que les résultats de l'APSP sont les plus fiables lorsque les données proviennent de relevés de terrain au sol ou d'une analyse par SIG de données satellitaires ou d'imagerie aérienne de fine résolution (≤ 0.5m/pixel). De plus, une vaste campagne de terrain réalisée dans le Haut-Arctique canadien montre que le patron ponctuel observé en un site donné est lié à la composition du substrat ainsi qu'à son stade relatif de développement. Finalement, en utilisant les résultats de terrain comme une source analogue qui nous informe sur l'interprétation des processus géomorphologiques sur Mars, un modèle d'évolution du paysage est développé pour expliquer le développement de formes de terrain peu documentées (depressions festonnées) dans les zones riches en glace des latitudes nord de Mars.
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Eckel, Stefanie. "Statistical analysis of spatial point patterns - applications to economical, biomedical and ecological data." [S.l. : s.n.], 2008. http://nbn-resolving.de/urn:nbn:de:bsz:289-vts-66022.
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Walsh, Daniel Charles Islip. "Detecting and extracting complex patterns from images and realizations of spatial point processes /." Thesis, Connect to this title online; UW restricted, 2000. http://hdl.handle.net/1773/8974.
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Carr, Jake Kenneth. "Retail Choice, Consumer Spaces, and Dynamics in the Spatial Organization of the Goods and Services Sector." The Ohio State University, 2017. http://rave.ohiolink.edu/etdc/view?acc_num=osu1500310205028892.
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Catella, Samantha A. "Investigating herbaceous layer plant community patterns: when does abiotic complexity matter?" Case Western Reserve University School of Graduate Studies / OhioLINK, 2019. http://rave.ohiolink.edu/etdc/view?acc_num=case1559905264222712.
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Barton, Mark B. "Spatial and Temporal Patterns of Arctic Nearshore Fish Community and Food Web Structures." FIU Digital Commons, 2018. https://digitalcommons.fiu.edu/etd/3735.
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Climate change and increasing anthropogenic activities are causing rapid changes to environmental and ecological processes in the Arctic Ocean. To better understand these changes, scientists have increased research efforts in these regions, but to date the number of studies on Arctic nearshore habitats are lacking. My dissertation responds to the paucity of information and investigates patterns in Arctic nearshore fish communities and food webs to gain insight to how these ecosystems may shift as these changes continue. I used multivariate statistical analysis to examine patterns in community structure and composition to determine that Arctic nearshore fish communities are largely driven by prey availability, salinity and temperature; and that species that are more abundant in warmer conditions are likely to increase in abundance as climatic conditions in the Arctic continue to warm. I improved the ability to apply stable isotope methods to Arctic food web studies by determining more appropriate model parameters using a laboratory-based isotope study on a common Arctic nearshore fish, and discuss its potential as a biological monitor species. These new parameters are used to confirm that a shift in prey resource dependence occurs across the seasonal shift from ice-covered winter to open-water summer conditions. Changes in basal resource dependence also occur later in the season across a latitudinal gradient where a shift to dependence on allochtonous inputs from nearby rivers increased trophic diversity. Using isotopic niche space theory, it was determined that the Arctic nearshore has a diverse prey base but that niche spaces of Arctic warm-water and cold-water species do overlap, and if numbers of warm-water fish continue to increase it will likely increase competition for resources for potentially less-adaptable, well-established, cold-water forage fish. On the other hand, if pelagic productivity is expected to increase and support larger fish biomasses, then there will be more than enough resources for warm-water and cold-water species to coexist, thus creating a more diverse prey base for piscivores in the Arctic.
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Hesselbarth, Maximilian H. K. [Verfasser], Kerstin [Akademischer Betreuer] Wiegand, Holger [Gutachter] Kreft, and Uta [Gutachter] Berger. "Analysing and modelling spatial patterns to infer the influence of environmental heterogeneity using point pattern analysis, individual-based simulation modelling and landscape metrics / Maximilian H. K. Hesselbarth ; Gutachter: Holger Kreft, Uta Berger ; Betreuer: Kerstin Wiegand." Göttingen : Niedersächsische Staats- und Universitätsbibliothek Göttingen, 2020. http://d-nb.info/1210264641/34.
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Jones-Todd, Charlotte M. "Modelling complex dependencies inherent in spatial and spatio-temporal point pattern data." Thesis, University of St Andrews, 2017. http://hdl.handle.net/10023/12009.
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Point processes are mechanisms that beget point patterns. Realisations of point processes are observed in many contexts, for example, locations of stars in the sky, or locations of trees in a forest. Inferring the mechanisms that drive point processes relies on the development of models that appropriately account for the dependencies inherent in the data. Fitting models that adequately capture the complex dependency structures in either space, time, or both is often problematic. This is commonly due to—but not restricted to—the intractability of the likelihood function, or computational burden of the required numerical operations. This thesis primarily focuses on developing point process models with some hierarchical structure, and specifically where this is a latent structure that may be considered as one of the following: (i) some unobserved construct assumed to be generating the observed structure, or (ii) some stochastic process describing the structure of the point pattern. Model fitting procedures utilised in this thesis include either (i) approximate-likelihood techniques to circumvent intractable likelihoods, (ii) stochastic partial differential equations to model continuous spatial latent structures, or (iii) improving computational speed in numerical approximations by exploiting automatic differentiation. Moreover, this thesis extends classic point process models by considering multivariate dependencies. This is achieved through considering a general class of joint point process model, which utilise shared stochastic structures. These structures account for the dependencies inherent in multivariate point process data. These models are applied to data originating from various scientific fields; in particular, applications are considered in ecology, medicine, and geology. In addition, point process models that account for the second order behaviour of these assumed stochastic structures are also considered.
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Filho, NarcÃlio de SÃ Pereira. "AnÃlise da dinÃmica espaÃo-temporal (1973 a 2014) das dunas de Jericoacoara, CearÃ, Brasil." Universidade Federal do CearÃ, 2014. http://www.teses.ufc.br/tde_busca/arquivo.php?codArquivo=15910.
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CoordenaÃÃo de AperfeÃoamento de Pessoal de NÃvel Superior<br>Dunas costeiras exercem um importante papel na manutenÃÃo do fluxo de sedimentos da zona costeira. O Parque Nacional de Jericoacoara, localizado no estado do CearÃ, regiÃo Nordeste do Brasil, possui uma morfologia pouco frequente, trata-se de um promontÃrio associado com um campo de dunas mÃveis denominadas barcanas, dunas individuais, de grande porte com formato de ferraduras que se deslocam em direÃÃo L â O. Elas realizam o by-pass, o transporte de sedimentos, essencial para a manutenÃÃo da linha de costa. Neste trabalho, foi priorizada a definiÃÃo da evoluÃÃo morfodinÃmica de dunas mÃveis isoladas (dunas Papai Noel, PÃr-do-Sol e Arraia), tendo como referencial teÃrico a anÃlise das paisagens e como procdimento tÃcnico principal a anÃlise espaÃo-temporal do recobrimento de imagens multitemporais dos satÃlites Landsat e Quickbird entre os anos de 1973 a 2014. AtravÃs da comparaÃÃo da distribuiÃÃo espaÃo temporal das morfologias dunares, nesse perÃodo de 41 anos, evidenciaram-se mudanÃas significativas na Ãrea, perÃmetro e deslocamento das dunas. Foi possÃvel constatar a aÃÃo dos fluxos de matÃria e energia vinculados com migraÃÃo continuada direcionada para a faixa de praia (setor de bypassing de sedimentos). A dinÃmica de migraÃÃo das dunas, quando analisadas apÃs as imagens de 2000, evidenciou possibilidades de alteraÃÃes dos aspectos morfolÃgicos influenciados pelo incremento do fluxo turÃstico, quando instituÃdo o PARNA de Jericoacoara. As mudanÃas foram mais significativas, sobretudo, entre os anos de 2001 a 2005, o que pode estar relacionado a uma maior intervenÃÃo humana (fluxo de turistas). A utilizaÃÃo das tÃcnicas de geoprocessamento para o mapeamento da evoluÃÃo morfodinÃmica do campo de dunas do Parque Nacional de Jericoacoara constituiu- se uma ferramenta essencial para a produÃÃo de informaÃÃes que certamente subsidiarÃo a continuidade do planejamento ambiental da referida, que se constitui como uma Unidade de ConservaÃÃo de ProteÃÃo Integral.<br>Coastal dunes play an important role in the sediment flow of the coastal zone. The unique morphology of the Jericoacoara National Park in the northeastern Brazilian state of Cearà consists of a promontory covered by a mobile dune field consisting of large, horseshoe-shaped dunes known locally as barcanas that migrate from east to west. These dunes are responsible for the by-pass, the transport of sediments essential for the maintenance of the coastline. The present study focused on the morphodynamic evolution of these isolated mobile dunes through the recovery of multitemporal Landsat and Quickbird satellite images from the years between 1975 and 2014. The comparison of the spatio-temporal distribution of the morphology of these dunes over this 41-year period revealed significant shifts in their area, perimeter, and movement. It was possible to confirm that the flow of material and energy were linked to a process of continuous migration in the direction of the beach (sediment bypassing sector). The dynamics of the dune migration in the years following 2000, when the national park was established, indicate possible impacts of the increase in tourism within the area on the morphology of the dunes. The changes were most significant between 2001 and 2005, possibly reflecting a greater influx of tourists and thus more intense anthropogenic impacts. The different geoprocessing techniques applied to the mapping of the morphodynamic evolution of the dune field of the Jericoacoara National Park proved to be an essential tool for the production of information that will guarantee the long-term environmental planning of this integral conservation unit.
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Allié, Élodie. "Assemblage des communautés d’arbres à une échelle locale en forêt tropicale : Apport d’une approche intégrative." Thesis, Guyane, 2016. http://www.theses.fr/2016YANE0003/document.
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Les forêts tropicales représentent un ‘hotspot’ de diversité avec un nombre considérable d’espèces qui coexistent jusqu’à une échelle locale fine. Plus particulièrement, 16 000 espèces d’arbres coexistent en Amazonie, 1 800 en Guyane française et entre 120 et plus de 200 espèces d’arbres par hectare. Cependant, le maintien de cette diversité face aux changements globaux actuels et à venir (qu’ils soient anthropiques ou climatiques…) est incertain. Avant de pouvoir prédire l’évolution de la diversité face aux changements globaux, un travail fondamental est nécessaire afin de comprendre les processus d’assemblage des communautés, processus qui maintiennent cette diversité. Ce travail est réalisé depuis de nombreuses années en écologie et reste d’actualité vu l’absence de consensus quant à l’importance relative des processus d’assemblage. Cette thèse s’inscrit dans la continuité de ce travail fondamental en utilisant une approche intégrative innovante, qui aborde de manière multi-échelle trois types de diversité : diversité taxonomique, fonctionnelle et phylogénétique. Nos résultats questionnent sur l'importance du filtrage environnemental quant aux propriétés hydrologiques et chimiques des sols, et sur celle des interactions biotiques dans l’assemblage de la communauté étudiée. Par ailleurs, nos résultats suggèrent que les distributions d’espèces puissent être influencées par la dynamique forestière en lien avec les chutes d’arbres et donc avec la disponibilité en lumière. Enfin, nous avons mis en évidence l’importance de la limitation de dispersion<br>Tropical forests are a biodiversity hotspot, with the coexistence of numerous species until a fine spatial scale. Particularly, 16.000 tree species coexist in Amazonia, 1.800 in Frenche Guiana and between 120 and more than 200 tree species per hectare. However, there are some uncertainties in maintaining diversity in regard to global changes. Hence before predicting the diversity evolution face of global changes, fundamental studies are needed to understand which assembly processes are involved in the maintenance of diversity. These fundamental studies still relevant given the lack of consensus on the relative importance of assembly processes. This thesis is a continuation of these fundamental studies, using innovative integrative approach, at multi-scale, to address three types of diversity: taxonomic diversity, functional and phylogenetic. Our results challenge the importance of environmental filtering for hydrological and chemical properties of soils, versus the importance of biotic interactions on community assembly. Furthermore, our results suggest that species distributions could be affected by forest dynamics related to falling trees and therefore by light availability. Finally, we have highlighted the importance of dispersal limitation on community assembly
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Call, Lara J. "Analysis of intraspecific and interspecific interactions between the invasive exotic tree-of-heaven (Ailanthus altissima (Miller) Swingle) and the native black locust (Robinia pseudoacacia L.)." Thesis, Connect to this title online, 2002. http://scholar.lib.vt.edu/theses/available/etd-05162002-132819/.
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Umande, Philip Pembe. "Spatial point pattern analysis with application to confocal microscopy data." Thesis, Imperial College London, 2008. http://hdl.handle.net/10044/1/8569.
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Currie, Janet Elizabeth. "Joint modelling of point process and geostatistical measurement data." Thesis, Lancaster University, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.268124.
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Ben, Cheikh Bassem. "Morphologie mathématique sur les graphes pour la caractérisation de l’organisation spatiale des structures histologiques dans les images haut-contenu : application au microenvironnement tumoral dans le cancer du sein." Thesis, Paris 6, 2017. http://www.theses.fr/2017PA066286/document.
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L'un des problèmes les plus complexes dans l'analyse des images histologiques est l'évaluation de l¿organisation spatiale des structures histologiques dans le tissu. En fait, les sections histologiques peuvent contenir un très grand nombre de cellules de différents types et irrégulièrement réparties dans le tissu, ce qui rend leur contenu spatial indescriptible d'une manière simple. Les méthodes fondées sur la théorie des graphes ont été largement explorées dans cette direction, car elles sont des outils de représentation efficaces ayant la capacité expressive de décrire les caractéristiques spatiales et les relations de voisinage qui sont interprétées visuellement par le pathologiste. On peut distinguer trois familles principales de méthodes des graphes utilisées à cette fin: analyse de structure syntaxique, analyse de réseau et analyse spectrale. Cependant, un autre ensemble distinctif de méthodes basées sur la morphologie mathématique sur les graphes peut être développé et adapté pour ce problème. L'objectif principal de cette thèse est le développement d'un outil capable de fournir une évaluation quantitative des arrangements spatiaux des structures histologiques en utilisant la morphologie mathématique basée sur les graphes<br>One of the most challenging problems in histological image analysis is the evaluation of the spatial organizations of histological structures in the tissue. In fact, histological sections may contain a very large number of cells of different types and irregularly distributed, which makes their spatial content indescribable in a simple manner. Graph-based methods have been widely explored in this direction, as they are effective representation tools having the expressive ability to describe spatial characteristics and neighborhood relationships that are visually interpreted by the pathologist. We can distinguish three main families of graph-based methods used for this purpose: syntactic structure analysis, network analysis and spectral analysis. However, another distinctive set of methods based on mathematical morphology on graphs can be additionally developed for this issue. The main goal of this dissertation is the development of a framework able to provide quantitative evaluation of the spatial arrangements of histological structures using graph-based mathematical morphology
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Protsiv, Sergiy. "Attraction and repulsion : modelling interfirm interactions in geographical space." Doctoral thesis, Handelshögskolan i Stockholm, Institutionen för Marknadsföring och strategi, 2012. http://urn.kb.se/resolve?urn=urn:nbn:se:hhs:diva-2154.
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More than three quarters of the world’s economic activity is concentrated in cities. But what drives people and firms to agglomerate in urban areas? Clearly, some places may offer inherent benefits due to the location itself, such as a mild climate or the presence of natural harbours, but that does not tell the whole story. Rather urban areas also offer spaces for interaction among people and firms as well as the proximity to potential partners, customers, and competitors, which could have a significant impact on the appeal of a location for a firm. Using multiple novel methods based on a unique detailed geographical dataset, this dissertation explores how a location’s attractiveness is impacted by the presence of nearby firms in three studies. The first study explores the influence of the density of economic activity on wages at a given location and attempts to disentangle the separate mechanisms that could be at work. The second study is concerned with the locations of foreign-owned firms and more specifically whether foreign-owned firms are more influenced by agglomeration benefits than domestic firms. The final study switches from modelling the effects of location to modelling the location patterns themselves using economic theory-based spatial point processes. The results of these studies make significant contributions to empirical research both in economic geography and international business as a set of theoretical propositions are tested on a very detailed dataset using an advanced methodology. The results could also be of interest for practitioners as the importance of location decisions is further reinforced, as well as for policymakers as the analyses explore not only the benefits but also the detriments of agglomeration. Sergiy Protsiv is a researcher at the Center for Strategy and Competitiveness at the Stockholm School of Economics. He participated in several projects on clusters and regional development, most notably the European Cluster Observatory.<br><p>Diss. Stockholm : Handelshögskolan, 2012</p>
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Wong, Ka Yiu. "Model-free tests for isotropy, equal distribution and random superposition in spatial point pattern analysis." HKBU Institutional Repository, 2015. https://repository.hkbu.edu.hk/etd_oa/202.
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This thesis introduces three new model-free tests for isotropy, equal distribution and random superposition in non-rectangular windows respectively. For isotropy, a bootstrap-type test is proposed. The corresponding test statistic assesses the discrepancy between the uniform distribution and the empirical normalised reduced second-order moment measure of a sector of fixed radius with increasing central angle. The null distribution of the discrepancy is then estimated by stochastic reconstruction, which generates bootstrap-type samples of point patterns that resemble the spatial structure of the given pattern. The new test is applicable for small sample sizes and is shown to have more robust powers to different choices of user-chosen parameter when compared with the asymptotic chi-squared test by Guan et al. (2006) in our simulation. For equal distribution, a model-free asymptotic test is introduced. The proposed test statistic compares the discrepancy between the empirical second-order product densities of the observed point patterns at some pre-chosen lag vectors. Under certain mild moment conditions and a weak dependence assumption, the limiting null distribution of the test statistic is the chi-squared distribution. Simulation results show that the new test is more powerful than the permutation test by Hahn (2012) for comparing point patterns with similar structures but different distributions. The new test for random superposition is a modification of the toroidal shift test by Lotwick and Silverman (1982). The idea is to extrapolate the pattern observed in a non-rectangular window to a larger rectangular region by the stochastic reconstruction so that the toroidal shift test can be applied. Simulation results show that the powers of the test applied to patterns with extrapolated points are remarkably higher than those of the test applied to the largest inscribed rectangular windows, with only slightly increased type I error rates. Real data sets are used to illustrate the advantages of the tests developed in this thesis over the existing tests in the literature.
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Romild, Ulla. "Essays on Distance Based (Non-Euclidean) Tests for Spatial Clustering in Inhomogeneous Populations : Adjusting for the Inhomogeneity through the Distance Used." Doctoral thesis, Uppsala : Acta Universitatis Upsaliensis, 2006. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-6829.
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Ben, Cheikh Bassem. "Morphologie mathématique sur les graphes pour la caractérisation de l’organisation spatiale des structures histologiques dans les images haut-contenu : application au microenvironnement tumoral dans le cancer du sein." Electronic Thesis or Diss., Paris 6, 2017. https://accesdistant.sorbonne-universite.fr/login?url=https://theses-intra.sorbonne-universite.fr/2017PA066286.pdf.
Full textAbstract:
L'un des problèmes les plus complexes dans l'analyse des images histologiques est l'évaluation de l¿organisation spatiale des structures histologiques dans le tissu. En fait, les sections histologiques peuvent contenir un très grand nombre de cellules de différents types et irrégulièrement réparties dans le tissu, ce qui rend leur contenu spatial indescriptible d'une manière simple. Les méthodes fondées sur la théorie des graphes ont été largement explorées dans cette direction, car elles sont des outils de représentation efficaces ayant la capacité expressive de décrire les caractéristiques spatiales et les relations de voisinage qui sont interprétées visuellement par le pathologiste. On peut distinguer trois familles principales de méthodes des graphes utilisées à cette fin: analyse de structure syntaxique, analyse de réseau et analyse spectrale. Cependant, un autre ensemble distinctif de méthodes basées sur la morphologie mathématique sur les graphes peut être développé et adapté pour ce problème. L'objectif principal de cette thèse est le développement d'un outil capable de fournir une évaluation quantitative des arrangements spatiaux des structures histologiques en utilisant la morphologie mathématique basée sur les graphes<br>One of the most challenging problems in histological image analysis is the evaluation of the spatial organizations of histological structures in the tissue. In fact, histological sections may contain a very large number of cells of different types and irregularly distributed, which makes their spatial content indescribable in a simple manner. Graph-based methods have been widely explored in this direction, as they are effective representation tools having the expressive ability to describe spatial characteristics and neighborhood relationships that are visually interpreted by the pathologist. We can distinguish three main families of graph-based methods used for this purpose: syntactic structure analysis, network analysis and spectral analysis. However, another distinctive set of methods based on mathematical morphology on graphs can be additionally developed for this issue. The main goal of this dissertation is the development of a framework able to provide quantitative evaluation of the spatial arrangements of histological structures using graph-based mathematical morphology
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Thapa, Mandira. "Optimal Feature Selection for Spatial Histogram Classifiers." Wright State University / OhioLINK, 2017. http://rave.ohiolink.edu/etdc/view?acc_num=wright1513710294627304.
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Barber, Michael R. "Effects of Hydraulic Dredging and Vessel Operation on Atlantic Sturgeon Behavior in a Large Coastal River." VCU Scholars Compass, 2017. http://scholarscompass.vcu.edu/etd/4792.
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The tidal James River, a focus of VCU's Atlantic Sturgeon program, supports both commercial shipping and hydraulic dredging. These anthropogenic threats present documented but preventable sources of mortality to the endangered species. Using three separate VEMCO Positioning System (VPS) receiver arrays, spatial data of previously-tagged fish were collected. ArcGIS and Programita software were used to analyze fish spatial distributions in the presence and absence of potential threats, using additional data including automatic identification system (AIS) vessel locations, vessel passages compiled using camera footage, and dredge records provided by the US Army Corps of Engineers. The data showed a change in distribution associated with vessels that varied according to river width but not vessel type. Dredging was associated with differences in spatial distribution, but more clearly for adults than sub-adults. The responses of Atlantic Sturgeon provide information necessary to propose potential threat mitigations, including seasonal restrictions for both vessels and dredging.
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Zhang, Weimin. "Topics in living cell miultiphoton laser scanning microscopy (MPLSM) image analysis." Texas A&M University, 2006. http://hdl.handle.net/1969.1/4412.
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Multiphoton laser scanning microscopy (MPLSM) is an advanced fluorescence
imaging technology which can produce a less noisy microscope image and minimize the
damage in living tissue. The MPLSM image in this research is the dehydroergosterol
(DHE, a fluorescent sterol which closely mimics those of cholesterol in lipoproteins and
membranes) on living cell's plasma membrane area. The objective is to use a statistical
image analysis method to describe how cholesterol is distributed on a living cell's
membrane. Statistical image analysis methods applied in this research include image
segmentation/classification and spatial analysis. In image segmentation analysis, we
design a supervised learning method by using smoothing technique with rank statistics.
This approach is especially useful in a situation where we have only very limited
information of classes we want to segment. We also apply unsupervised leaning methods
on the image data. In image data spatial analysis, we explore the spatial correlation of
segmented data by a Monte Carlo test. Our research shows that the distributions of DHE
exhibit a spatially aggregated pattern. We fit two aggregated point pattern models, an
area-interaction process model and a Poisson cluster process model, to the data. For the area interaction process model, we design algorithms for maximum pseudo-likelihood
estimator and Monte Carlo maximum likelihood estimator under lattice data setting. For
the Poisson Cluster process parameter estimation, the method for implicit statistical
model parameter estimate is used. A group of simulation studies shows that the Monte
Carlo maximum estimation method produces consistent parameter estimates. The
goodness-of-fit tests show that we cannot reject both models. We propose to use the area
interaction process model in further research.
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GILARDI, ANDREA. "Statistical Models and Data Structures for Spatial Data on Road Networks." Doctoral thesis, Università degli Studi di Milano-Bicocca, 2021. http://hdl.handle.net/10281/314016.
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Negli ultimi anni è nato un interesse sempre crescente verso l’analisi statistica di dati spaziali aventi supporto di network. Gli esempi più classici di questa tipologia di eventi sono, ad esempio, gli incidenti stradali, i furti di auto, i crimini, e gli interventi delle ambulanze, mentre le linee che compongono la network rappresentano tipicamente le strade, i fiumi, i binari della ferrovia, oppure le terminazioni nervose.
L’analisi di questi fenomeni è interessante sotto diversi punti di vista. Innanzitutto, i modelli statistici presentano diverse problematiche legate al supporto spaziale. Per questo motivo, negli ultimi anni sono stati pubblicati diversi paper che mostrano le difficoltà principali legate alla natura stessa della network. Inoltre, il recente sviluppo di database spaziali open source (quali Open Street Map) ha permesso il download e la creazione di dataset che coprono le reti stradali di quasi tutto il mondo. L’enorme mole di dati e gli (inevitabili) errori geometrici presenti nei database di Open Street Map rappresentano due problematiche ulteriori. Infine, dato che al momento la maggior parte dei pacchetti R per l’analisi di dati su network sono ancora in fase di sviluppo, esistono anche diverse difficoltà computazionali e problemi nell’implementazione di metodologie nuove.
Questo lavoro di tesi riassume quattro articoli che presentano strutture dati e metodologie statistiche per l’analisi di dati spaziali aventi supporto di network, considerando sia un approccio di tipo network-lattice che un approccio di tipo point-pattern.
Il primo paper presenta una revisione bibliografica dei pacchetti R che implementano classi e funzioni per l’analisi di network stradali, concentrandosi in particolare su stplanr e dodgr. Vengono introdotte le principali routines legate al calcolo di shortest paths e centrality
measures utilizzando dataset via via più complessi.
Il secondo lavoro presenta un modello di Poisson Dinamico Zero Inflated per la stima di due indici di rischiosità relativi agli incidenti stradali avvenuti nel network di Milano dal 2015 al 2017. L’unità statistica elementare è rappresentata dal singolo segmento di strada, mentre la variabile risposta misura il numero di incidenti avvenuti in ognuno dei tre anni. Viene impiegato un insieme di covariate demografiche e strutturali estratte da Open Street Map e dai dati del censimento italiano avvenuto nel 2011.
Il terzo paper introduce un modello Bayesiano gerarchico multivariato per la stima della rischiosità stradale tramite un approccio di tipo network-lattice. Ci si è concentrati sul network stradale della città di Leeds e su due diverse tipologie di incidenti. La componente spaziale è stata modellata tramite un errore casuale di tipo Multivariate CAR, mentre le correlazioni residue sono state catturate tramite un errore casuale non strutturato. Infine, si è anche sviluppata una metodologia nuova per l’analisi di MAUP su dati di tipo network-lattice.
Per concludere, il quarto articolo presenta un insieme di risultati preliminari relativi all’analisi spazio-temporale di point pattern su network tramite processi di Poisson non-omogenei. In particolare, si è analizzata la distribuzione degli interventi delle ambulanze nel comune di Milano tra il 2015 ed il 2017, sviluppando un modello a fattori latenti per la componente temporale ed uno stimatore kernel non-parametrico per l’intensità spaziale, riadattato nel caso di dati su reticolo.
La tesi si compone anche di tre appendici. Le prima riassume le caratteristiche di base del software e della metodologia INLA, la seconda presenta i materiali addizionali legati al quarto capitolo, mentre la terza appendice introduce un pacchetto R chiamato osmextract, utilizzato per manipolare dati da Open Street Map.
Il quinto capitolo conclude la tesi, riassumendo i risultati principali e introducendo alcuni sviluppi futuri.<br>In the last years, we observed a surge of interest in the statistical analysis of spatial data lying on or alongside networks. Car crashes, vehicle thefts, bicycle incidents, roadside kiosks, neuroanatomical features, and ambulance interventions are just a few of the most typical examples, whereas the edges of the network represent an abstraction of roads, rivers, railways, cargo-ship routes or nerve fibers.
This type of data is interesting for several reasons. First, the statistical analysis of the events presents several challenges because of the complex and non-homogeneous nature of the network, which creates unique methodological problems. Several authors discussed and illustrated the common pitfalls of re-adapting classical planar spatial models to network data. Second, the rapid development of open-source spatial databases (such as Open Street Map) provides the starting point for creating road networks at a wide range of spatial scales. The size and volume of the data raise complex computational problems, while common geometrical errors in the network’s software representations create another source of complexity. Third, at the time of writing, the most important software routines and functions (mainly implemented in R) are still in the process of being re-written and readapted for the new spatial support.
This manuscript collects four articles presenting data structures and statistical models to analyse spatial data lying on road networks using point-pattern and network-lattice approaches.
The first paper reviews classes, vital pre-processing steps and software representations to manipulate road network data. In particular, it focuses on the R packages stplanr and dodgr, highlighting their main functionalities, such as shortest paths or centrality measures, using a range of datasets, from a roundabout to a complete network covering an urban city.
The second paper proposes the adoption of two indices for assessing the risk of car crashes on the street network of a metropolitan area via a dynamic zero-inflated Poisson model. The elementary statistical units are the road segments of the network. It employs a set of open-source spatial covariates representing the network’s structural and demographic characteristics (such as population density, traffic lights or crossings) extracted from Open Street Map and 2011 Italian Census.
The third paper demonstrates a Bayesian hierarchical model for identifying road segments of particular concern using a network-lattice approach. It is based on a case study of a major city (Leeds, UK), in which car crashes of different severities were recorded over several years. It includes spatially structured and unstructured random effects to capture the spatial nature of the events and the dependencies between the severity levels. It also recommends a novel procedure for estimating the MAUP (Modifiable Areal Unit Problem) for network-lattice data.
Finally, the fourth paper summarises a set of preliminary results related to the analysis of spatio-temporal point patterns lying on road networks using non-homogeneous Poisson processes. It focuses on the ambulance interventions that occurred in the municipality of Milan from 2015 to 2017, developing two distinct models, one for the spatial component and one for the temporal component. The spatial intensity function was estimated using a network readaptation of the classical non-parametric kernel estimator.
The first two appendices briefly review the basics of INLA methodology, the corresponding R package and the supplementary materials related to the fourth chapter, while the third appendix briefly introduces an R package, named osmextract, that was developed during the PhD and focuses on Open Street Map data.
The fifth chapter concludes the manuscript, summarising the main contributions and emphasising
future research developments.
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Chen, Yan. "Spatial Analysis of Fatal Automobile Crashes in Nashville, TN, 2001-2011." TopSCHOLAR®, 2013. http://digitalcommons.wku.edu/theses/1300.
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With increasing levels of motor vehicle ownership, automobile crashes have become a serious public issue in the U.S. and around the world. Knowing when, where, and how traffic accidents happen is critical in order to ensure road safety and to plan for adequate road infrastructure. There is a rich body of literature pertaining to time-related fatal crashes, most of which focuses on non-spatial factors such as a driver’s visibility at night, drinking and drug use, and road conditions. These studies provide a theoretical basis for understanding the causes of crashes from a non-spatial perspective, and a number of traffic laws and policies consequently have been enacted to minimize the impacts of non-spatial factors. Over the past few years, advances in Geographic Information Systems (GIS) have greatly enhanced our ability to analyze traffic accidents from a spatial perspective. This study aims to fill a void in traffic safety studies by comparing and analyzing the differences in the spatial distribution of fatal crashes based on temporal factors, specifically in three periods: 1) day and night; 2) A.M. rush hours and P.M. rush hours; and 3) weekdays and weekends. With the Nashville Metropolitan Area as the study area, the research utilized a number of spatial point-pattern analysis (SPPA) methods, including planar KDE, planar global auto K function, network global cross K functions, and network local cross K functions. All fatal crashes in the Nashville area were found to be clustered and generally follow the patterns of average daily traffic flow. All time-based subtypes of fatal crashes also were found to be concentrated within the central urban area of Nashville, mostly along major roads, and especially near major road intersections and highway interchanges. No notable spatial differences were detected among the subtypes of fatal crashes when applying network global cross K function. However, with the help of the network local cross K function, some localized spatial differences were identified. Some specific locations of hotspots of nighttime and P.M. rush hour fatal crashes were found not to be at the same locations as those at of daytime and A.M. rush hour fatal crashes, respectively. The approach adopted in this study not only provides a new way to analyze spatial distribution of spatial point events such as fatal crashes, but it also can be applied readily to real-world applications. A good understanding of where these spatial differences are should help various agencies practice effective measures and policies in order to improve road conditions, reduce traffic accidents, and ensure road safety.
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Reckin, Rachel Jean. "Mountains as crossroads : temporal and spatial patterns of high elevation activity in the Greater Yellowstone ecosystem, USA." Thesis, University of Cambridge, 2018. https://www.repository.cam.ac.uk/handle/1810/278102.
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In the archaeological literature, mountains are often portrayed as the boundaries between inhabited spaces. Yet occupying high elevations may have been an adaptive choice for ancient peoples, as rapidly changing elevations also offer variation in climate and resources over a relatively small area. So what happens, instead, if we put mountain landscapes at the center of our analyses of prehistoric seasonal rounds and ecological adaptation? This Ph.D. argues that, in order to understand any landscape that includes mountains, from the Alps to the Andes, one must include the ecology and archaeology of the highest elevations. Specifically, I base my findings on new fieldwork and lithic collections from the Absaroka and Beartooth Mountains in the Greater Yellowstone Ecosystem (GYE) of the Rocky Mountains, which was a vital crossroads of prehistoric cultures for more than 11,000 years. I include five interlocking analyses. First, I consider the impacts of anthropogenic climate change on high elevation cultural resources, focusing on the diminishing resiliency of ancient high elevation ice patches and the loss of the organic artifacts and paleobiological materials they contain. Second, I create a dichotomous key for chronologically typing projectile points, suggesting a methodological improvement for typological dating in the GYE and for surface archaeology more broadly. Third, I use obsidian source data to consider whether mountain people were a single, unified group or were represented by a variety of peoples with different zones of land tenure. Fourth, I consider high elevation occupation in both mountain ranges as part of the seasonal round, using indices of diversity in tool types and raw material to study how the duration of those occupations changed through time. And, finally, I test the common contention that ancient people primarily used mountains as refugia from extreme climatic pressure at lower elevations. Ultimately, I find that, in both mountain ranges, increased high elevation activity is most highly correlated with increased population, not with hot, dry climatic conditions. In other words, the mountains were more than simply refugia for plains or basin people to occupy when pressured by climatic hardship. In addition, between the Absarokas and the Beartooths the evidence suggests two different patterns of occupation, not a monolithic pan-mountain adaptation. These results demonstrate the potential contributions of surface archaeology to our understanding of prehistory, and have important implications for the way we think about mountain landscapes as peopled spaces in relation to adjacent lower-elevation areas.
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Petit, Geoffrey. "Etude des facteurs de risque et de pathogénicité et de l’évolution spatio-temporelle de la maladie de l’œdème chez le sanglier (Sus scrofa) en Ardèche." Thesis, Université Clermont Auvergne (2017-2020), 2019. http://www.theses.fr/2019CLFAC036/document.
Full textAbstract:
La maladie de l’œdème est une maladie connue depuis de nombreuses années chez le porc. Les premiers cas recensés dans une population de suidés sauvages sont apparus en 2013 en Ardèche. Un nouveau foyer de cette maladie est ensuite apparu en 2016 dans les Pyrénées-Orientales à la frontière entre la France et l’Espagne. Comprendre les facteurs permettant son apparition ainsi que sa transmission est nécessaire afin d’anticiper de futures mortalités dues à cette maladie. Dans cette thèse, une analyse épidémiologique de cette maladie chez le sanglier a été réalisée. Des clusters de mortalités sont alors apparus et ont permis de mettre en évidence une possible source de contamination unique et récurrente dans le temps. La mise en place d’une nouvelle méthode pour étudier la détectabilité des cadavres de sanglier a souligné la difficulté de retrouver des cadavres de sanglier en forêt. La dernière analyse épidémiologique à partir d’un modèle de type « Spatial point pattern » a mis en avant de possibles facteurs de risque d’apparition et de transmission qui ont ensuite été analysés plus précisément. L’analyse des données issus des tableaux de chasse en Ardèche a été réalisée afin de détecter des variations de la densité et du ratio J/A des populations de sanglier suggérant un stress alimentaire chez le sanglier, un prodrome ou une conséquence de la maladie. Aucun stress alimentaire ne fut détecté lors de cette analyse. Des hypothèses ont pu être émises pour expliquer certaines variations observées : i) la conséquence directe de la maladie, ii) un phénomène environnemental particulier et iii) un évènement pathogénique. La piste de l’événement pathogénique a été approfondie avec la découverte du SDRP (syndrome dysgénésique et respiratoire du porc). Les interactions porcs-sangliers, nombreuses en Ardèche, ont été déterminées comme potentiellement responsables du passage de la bactérie entre le compartiment domestique et sauvage. Une étude génétique a également été effectuée pour investiguer le gène alpha-1-fucosyltransferase associé à la sensibilité du porc à la maladie. Tous les sangliers analysés étaient sensibles à la maladie. D’autres analyses complémentaires sont nécessaires afin de comprendre au mieux cette maladie ainsi que les différents facteurs de risque pour l’apparition mais également la transmission<br>Edema disease has been a known disease in pigs for many years. The first cases recorded in a population of wild suids appeared in 2013 in Ardèche. A new outbreak of this disease then emerged in 2016 in the Pyrénées-Orientales on the border between France and Spain. Understanding the factors that enable its onset and transmission is necessary to anticipate future mortality from this disease. In this thesis, an epidemiological analysis of this disease in wild boar was carried out. Clusters of mortalities then emerged, highlighting a possible single and recurrent source of contamination over time. The introduction of a new method to study the detectability of wild boar corpses highlighted the difficulty of finding wild boar corpses in the forest. The latest epidemiological analysis using a Spatial point pattern model highlighted possible risk factors for onset and transmission, which were then analysed more precisely. Analysis of data from hunting tables in the Ardèche was carried out in order to detect variations in the density and J/A ratio of wild boar populations suggesting food stress in the wild boar, a prodrome or consequence of the disease. No dietary stress was detected during this analysis. Assumptions could be made to explain some observed variations: i) the direct consequence of the disease, ii) a particular environmental phenomenon and iii) a pathogenic event. The trail of the pathogenic event was deepened with the discovery of the PRRS (Pork Respiratory and Dygesic Syndrome). The pig-boar interactions, numerous in the Ardeche, were determined as potentially responsible for the passage of the bacteria between the domestic and wild compartment. A genetic study was also conducted to investigate the alpha-1-fucosyltransferase gene associated with the susceptibility of pigs to the disease. All the wild boars tested were susceptible to the disease.Further further analysis is needed in order to better understand this disease as well as the different risk factors for both onset and transmission
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Bauman, David. "Analyses spatialement explicites des mécanismes de structuration des communautés d'arbres." Doctoral thesis, Universite Libre de Bruxelles, 2018. http://hdl.handle.net/2013/ULB-DIPOT:oai:dipot.ulb.ac.be:2013/276814.
Full textAbstract:
La compréhension des processus écologiques qui sous-tendent l’assemblage des communautés végétales et la coexistence des espèces est un objectif central en écologie. Ces processus sont potentiellement nombreux et de natures contrastées. Ainsi, la composition d’une communauté de plantes dépend de processus déterministes liés aux conditions environnementales abiotiques (climat, conditions physiques et chimiques du sol, lumière) et d’interactions biotiques complexes, positives (facilitation, symbioses) comme négatives (compétition, prédation, pathogènes). En outre, les communautés sont influencées par des processus stochastiques (capacité de dispersion limitée, dérive écologique). Si les mécanismes à l’origine de ces processus sont très différents, ils ont néanmoins en commun la génération de motifs (patterns) spatiaux de distribution d’espèces dans les communautés. L’analyse de la structure spatiale des communautés permet ainsi une étude indirecte des processus régissant les communautés. La nature complexe de ces patterns spatiaux a mené au développement de nombreuses méthodes statistiques de détection et de description de patterns. Les méthodes basées sur des vecteurs propres spatiaux sont parmi les plus puissantes et précises pour détecter des patterns complexes et multi-échelles. Ces vecteurs propres, utilisés comme prédicteurs spatiaux, peuvent être combinés à un ensemble de variables environnementales dans un cadre de partition de variation. Celui-ci permet, en théorie, de démêler les effets uniques et l’effet conjoint des variables environnementales et spatiales sur la variation de composition d’une communauté. Il mène ainsi à une quantification de l’action des processus déterministes et des processus stochastiques sur l’assemblage de la communauté. Néanmoins, je montre dans cette thèse qu’un certain flou méthodologique concernant deux étapes déterminantes des analyses basées sur les vecteurs propres spatiaux a mené une proportion élevée d’études à utiliser ces méthodes de manière sous-optimale, voire fortement biaisée. Ceci compromet la fiabilité des patterns spatiaux détectés et des processus écologiques inférés. Une autre limitation de ce cadre d’analyse concerne la fraction de la partition de variation décrivant l’effet environnemental spatialement structurés qu’aucune méthode ne permet de tester.Cette thèse présente des solutions non biaisées, puissantes et précises à ces différentes limitations méthodologiques et permet d’élargir le cadre de l’inférence de processus écologique à partir de patterns spatiaux de communautés. Les différentes étapes d’amélioration de ces méthodes ont également été illustrées dans la thèse au travers de trois cas d’études fournis par deux communautés d’arbres tropicale et tempérée et une communauté de champignons symbiotiques des arbres.<br>Doctorat en Sciences<br>info:eu-repo/semantics/nonPublished
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Mamuse, Antony. "Spatial statistical estimation of undiscovered mineral endowment: case of komatiite-associated nickel sulphide resources, Kalgoorlie Terrane, Western Australia." Thesis, Curtin University, 2010. http://hdl.handle.net/20.500.11937/449.
Full textAbstract:
The Kalgoorlie Terrane of the Yilgarn Craton, Western Australia, containing about 60% (~11 Mt) of the world’s known komatiite-hosted nickel sulphide resources, is the world’s best studied and economically most important province for this mineral deposit type. Although increasingly mature in terms of nickel exploration, the Kalgoorlie Terrane is believed to contain significant additional undiscovered nickel endowment. Using the data-rich Kalgoorlie Terrane, this thesis develops a benchmark methodology that combines geological knowledge with spatial analysis and mathematical-statistical methods to estimate undiscovered nickel resources.In the proposed methodology, nickel sulphide deposits are considered realisations of stochastic mineralisation processes and are analysed within the following framework. Komatiites in the Kalgoorlie Terrane constitute the full sample space or the permissive tract. Disjoint, naturally bound individual komatiite bodies that make up the sample space are used as the spatial analysis units. Some komatiite bodies within the sample space contain nickel sulphide deposits (mineralised) and others do not (unmineralised). In this study, the most explored mineralised komatiite bodies constitute local control areas against which nickel resources in the less explored komatiite bodies can be assessed. The concept of local control areas is analogous to the concept of global control areas which are well explored parts of permissive areas for particular deposit types worldwide.Spatial point pattern analyses showed that the spatial distribution of mineralised komatiite bodies within the sample space is clustered. In contrast, nickel sulphide deposits in individual komatiite bodies are either randomly distributed or dispersed, and not clustered. This absence of deposit clustering within individual komatiite bodies indicates that the intensity of the deposit pattern of each komatiite body may be adequately expressed as deposit density (number of deposits per km[superscript]2). In global quantitative resource assessments, regression analysis of the well established power law relationship between deposit density and size of global control areas provides a robust method for estimating the number of deposits.In this study a power law relationship reminiscent of that in global models was found between the sizes of control areas and deposit density. In addition, this study establishes another power law relationship between nickel endowment density (nickel metal per km[superscript]2) and the sizes of control areas. Deposit and endowment density regression models based on the two power laws suggested that, respectively, 59 to 210 (mean 114) nickel sulphide deposits and 3.0 to 10.0 Mt (mean 5.5 Mt) nickel metal remained undiscovered in demonstrably mineralised komatiite bodies within the Kalgoorlie Terrane. More emphasis is placed on endowment density which may be more intrinsic to the Kalgoorlie Terrane than deposit density because deposit counts are confounded by definitional ambiguities emanating from orebody complexities. Thus the spatial pattern of mineral deposits may not coincide with the spatial pattern of mineral endowment as demonstrated by spatial centrographic analyses in this study.To estimate the amount of undiscovered nickel metal in the entire Kalgoorlie Terrane and not just in the demonstrably mineralised komatiite bodies, Zipf’s law was applied. According to Zipf’s law, the size of the largest deposit is twice the size of the second, thrice the size of the third, four times the fourth, and so on. Based on the currently known size of Mt. Keith deposit, the largest nickel sulphide deposit in the Kalgoorlie Terrane, Zipf’s law indicates that the terrane is nearly mature in terms of nickel exploration and contains only about 3.0 Mt nickel metal in undiscovered resources. The collective implication of the regression and Zipf’s law estimates is that in the Kalgoorlie Terrane, no significant nickel resources are likely to be contained in the known komatiites that are presently not demonstrably mineralised. However if, as widely speculated, the actual size of Mt. Keith deposit is about twice the currently known size, Zipf’s law predicts 10.0 Mt nickel metal in undiscovered nickel endowment for the Kalgoorlie Terrane. The additional 7.0 Mt undiscovered nickel metal endowment is attributed to opening up of a new exploration search space through deeper resource delineation, within an otherwise nearly mature terrane.
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Menin, Aline. "eSTIMe : un environnement de visualisation pour l'analyse multi-points de vue des mobilités quotidiennes." Thesis, Université Grenoble Alpes, 2020. http://www.theses.fr/2020GRALS010.
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Le domaine de recherche de la mobilité urbaine vise l'observation et la conception des déplacements humains dans un environnement urbain, dont les informations aident à la prise de décision et à la résolution de problèmes dans le cadre des politiques publiques. De nombreux experts - pas nécessairement spécialistes des transports - doivent traiter des données urbaines plus ou moins standardisées pour en extraire des connaissances synthétiques et facilement exploitables. De ce fait, les agences de transport public mènent couramment des enquêtes de déplacements pour recueillir des informations sur les déplacements quotidiens de la population sur un territoire donné, dont les jeux de données résultant sont larges et complexes en requierant une analyse qui croise les dimensions spatiales, temporelles, thématiques et socio-économiques pour permettre de découvrir les schémas spatio-temporels de la mobilité quotidienne. Dans ce contexte, la visualisation d'informations est une approche appropriée pour soutenir l'analyse des données de mobilité urbaine, puisque les analystes n'ont pas à apprendre des méthodes sophistiquées pour interpréter les visualisations de données qui viennent renforcer leur cognition et permettent la découverte d'aperçus non structurés dans les données.Ainsi, nous proposons un cadre de visualisation pour aider à l'analyse de la mobilité urbaine à travers des indicateurs décrivant des objets d'intérêt complémentaires au sein des données qui permettent d'aborder trois catégories de questions sous-jacentes au phénomène de la mobilité urbaine. Une première question est de savoir comment les habitants d'un territoire se déplacent au quotidien et quels processus d'échanges entre les lieux cela génère, ce qui l'on peut analyser par l'exploration des quantités, des modalités, de la direction et de la variation des flux et des déplacements en fonction des différents aspects socio-économiques des individus et des types d'espaces. Une deuxième question concerne la variation temporelle de la présence de la population sur un territoire, qui permet de comprendre l'utilisation de différents ``sours-espaces'' en tenant compte des caractéristiques socio-économiques des personnes qui s'y rendent et des activités qu'elles y exercent. La troisième question cherche à expliquer le besoin de déplacement des individus à travers l'ordre temporel des déplacements et des activités des individus (aussi nommés ``trajectoires quotidiennes'') dans le contexte spatial du territoire.Nous proposons un cadre visuel à l'aide de la dérivation et l'exploration visuelle d'indicateurs décrivant le territoire, les flux et les déplacements, et les trajectoires quotidiennes, sur de multiples granularités spatio-temporelles et attributs thématiques. Notre interface de visualisation permet de disperser les représentations visuelles sur de multiples tableaux de bords analytiques, permettant aux utilisateurs de personnaliser l'agencement spatial des visualisations et les indicateurs de manière significative en fonction de l'analyse en cours. De plus, nous proposons une interaction basée sur le mouvement, qui repose sur l'inclinaison d'une tablette et qui permet d'explorer la variation temporelle des indicateurs en tirant parti d'une entrée tactile et tangible. La conception de notre approche de visualisation a suivi un processus d'évaluation interactif qui comprend des évaluations successives auprès des utilisateurs visant à affiner un prototype afin d'atteindre la performance et la satisfaction de l'utilisateur<br>The research field of urban mobility aims at the observation and design of human trips within an urban environment, which information supports decision-making and problem solving within public policies. In this context, there are many experts -- not necessarily transportation specialists -- that need to handle more or less standardized urban data to extract synthetic and easily exploitable knowledge. Hence, public transportation agencies commonly conduct trip-based surveys to collect information about day-to-day travel of the population within a particular territory (i.e. where and when we travel), resulting in large and complex datasets which analysis requires crossing spatial, temporal, thematic and socioeconomic dimensions to enable discoveries of daily urban mobility patterns. This way, information visualization is a suitable approach to support the analysis of urban mobility data, since analysts do not have to learn sophisticated methods to interpret the data visualizations that come to reinforce their cognition and enable the discovery of unstructured insights within the data.Thereby, we propose a visualization framework to assist the analysis of urban mobility through indicators describing complementary objects of interest within the data that allow to address three categories of questions underlying the urban mobility phenomenon. A first question seeks to understand the daily traveling routine of a population and the resulting processes of exchange between places, which can be studied through the exploration of amounts, modalities, direction, and variation of travel flows and trips according to different socioeconomic aspects of individuals and land types. A second questioning concerns the temporal variation of population presence throughout a territory, which allows to understand the use of distinct locations by taking into account the socioeconomic characteristics of the people visiting it and the activities they carry out there. The third question seeks to explain the individuals' need of traveling by studying the temporal ordering of trips and activities of individuals (i.e. daily trajectories) within the spatial context of the territory.Our framework supports the derivation and visual exploration of indicators describing the territory, travel flows and trips, and daily trajectories, over multiple spatio-temporal resolutions and thematic attributes. Our visualization interface allows to disperse visual representations over multiple analytical displays, enabling users to customize the spatial arrangement of visualizations and indicators in meaningful ways according to the ongoing analysis. Furthermore, we propose a movement-based interaction based on the tilting of a tablet that allows to explore the temporal variation of indicators leveraging tactile and tangible input. The conception of our visualization approach followed an interactive evaluation process that consists of successive user-based evaluations aiming to refine a prototype in order to achieve user performance and satisfaction
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Bui, Manh Hung. "Structure and restoration of natural secondary forests in the Central Highlands, Vietnam." Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2016. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-216210.
Full textAbstract:
Introduction and objectives
In Vietnam, the forest resources have been declining and degrading severely in recent years. The degradation has decreased the natural forest area, changed the forest structure seriously and reduced timber volume and biodiversity. From 1999 to 2005, the rich forest area has decreased 10.2%, whereas the poor secondary forest has increased dramatically by 20.7%. Forest structure plays an important role in forestry research. Understanding forest structure will unlock an understanding of the history, function and future of a forest ecosystem (Spies, 1998). The forest structure is an excellent basis for restoration measures. Therefore, this research is necessary to contribute to improving forest area and quality, reducing difficulties in forest management. The study also enhances the grasp of forest structure, structure changes after harvesting and fills serious gaps in knowledge. In addition, the research results will contribute to improving and rescuing the poor secondary forest and restoring it, approaching the old-growth forest in Vietnam.
Material and methods
The study was conducted in Kon Ka Kinh national park. The park is located in the Northeastern region of Gia Lai province, 50 km from Pleiku city center to the Northeast. The park is distributed over seven different communes in three districts: K’Bang, Mang Yang and Đăk Đoa. Data were collected from 10 plots of secondary forests (Type IIb) and 10 plots of primeval forests (Type IV). Stratified random sampling was applied to select plot locations. 1 ha plots were used to investigate gaps. 2000 m2 plots were used to measure overstorey trees such as diameter at breast height, total height, crown width and species names. 500 m2 subplots were used to record tree positions. For regeneration, 25 systematic 4 m2 subplots were established inside 1 ha plots. After data were collected in the field, data analyses were conducted by using R and Excel. Firstly, some stand information, such as density, volume and so on, was calculated, and then descriptive statistics were computed for diameter and height variables. Linear mixed effect models were applied to analyze the difference of diameter and height and to check the effect of random factor between the two forest types. Diameter and height frequency distributions were also generated and compared by using permutational analysis of variance (PERMANOVA). Non-linear regression models were analyzed for diameter and height variables. Similar analyses were implemented for gaps. Regarding spatial point patterns of overstorey trees, replicated point pattern analysis techniques were applied in this research. For biodiversity, some calculations were run such as richness and biodiversity indices, comparison of biodiversity indices by using linear mixed models and biodiversity differences between two forest types tested again by permutational analysis of variance. In terms of regeneration, some analyses were implemented such as: height frequency distribution generation, frequency difference testing, biodiversity indices for the regeneration and spatial distribution checking by using a nonrandomness index.
Results and discussion
After analyzing the data, some essential findings were obtained as follows: Hypothesis H1 “The overstorey structure of secondary forests is more homogeneous and uniform than old-growth forests” is accepted. In other words, the secondary forest density is about 1.8 times higher than the jungle. However, the volume is only 0.56 times as large. The average diameter and height of the secondary forest is smaller by 5.71 cm and 3.73 m than the old-growth forest, respectively. Linear mixed effect model results indicate that this difference is statistically different and the effect of the random factor (Section) is not important. Type IIb has many small trees and the diameter frequency distribution is quite homogeneous. The old-growth forest has more big trees. For both forest stages, the height frequency distribution is positively skewed. PERMANOVA results illustrate that the frequency distribution is statistically different between the two forest types. Regression functions are also more variant and diverse in the old-growth forest, because all standard deviations of the parameters are greater there. Gap analysis results indicate that the number of gaps in the young forest is slightly higher, while the average gap size is much smaller. The gap frequency distribution is statistically different between the two types. In terms of the spatial point pattern of overlayer trees, the G-test and the pair correlation function results show that trees distribute randomly in the secondary forest. In contrast, the spatial point patterns of trees are more regular and diverse in the old-growth forest. The spatial point pattern difference is not significant, and this is proved by a permutational t-test for pair correlation function (pcf). Envelope function results indicate that the variation of pcf in young forests is much lower than in the primary forests.
Hypothesis H2 “The overstorey species biodiversity of the secondary forest is less than in the old-growth forest” is rejected. Results show that the number of species of the secondary forest is much greater than in the old-growth forest, especially richness. The richness of the secondary forest is 1.16 times higher. The Simpson and Shannon indices are slightly smaller in the secondary forest. The average Simpson index for both forest stages is 0.898 and 0.920, respectively. However, the difference is not significant. Species accumulation curves become relatively flatter on the right, meaning a reasonable number of plots have been observed. Estimated number of species from accumulation curves in two forest types are 105 and 95/ha. PERMANOVA results show that number of species and proportion of individuals in each species are significantly different between forest types.
Hypothesis H3 “The number regenerating species of the secondary forest is less and they distribute more regularly, compared to the old-growth forest” is rejected. There are both similarities and differences between the two types. The regeneration density of the stage IIb is 22,930 seedlings/ha, greater than the old forest by 9,030 seedlings. The height frequency distribution shows a decreasing trend. Similar to overstorey, the richness of the secondary forest is 141 species, higher than the old-growth forest by 9 species. Biodiversity indices are not statistically different between two types. PERMANOVA results indicate that the number of species and the proportion of individuals for each species are also not significantly different from observed forest types. Nonrandomness index results show that the regeneration distributes regularly. Up to 95% of the plots reflect this distribution trend.
Hypothesis H4 “Restoration measures (with and without human intervention) could be implemented in the regenerating forest” is accepted. The investigated results show that the secondary forest still has mother trees, and it has enough seedlings to restore. Therefore, restoration solutions with and without human intervention can be implemented. Firstly, forest protection should be applied. This measure is relevant to national park regulations in Vietnam. Rangers and other related organizations will be responsible for carrying out protection activities. These activities will protect forest resources from illegal logging, grazing and tourist activities. Environmental education and awareness-raising activities for indigenous people is also important. Another measure is additional and enrichment planting. It should focus on exclusive species of the overstorey in Type IIb or exclusive species of the primary forest. Selection of these species will lead to species biodiversity increase in the future. This also meets the purpose of the maximum biodiversity solution.
Conclusion
Forest resources play a very important role in human life as well as maintaining the sustainability of ecosystems. However, at present, they are under serious threat, particularly in Vietnam. Central Highland, Vietnam, where forest resources are still relatively good, is also threatened by illegal logging, lack of knowledge of people and so on. Therefore, it needs the hands of the people, especially foresters and researchers. Through research, scientists can provide the knowledge and understanding of the forest, including the structure and forest restoration. This study has obtained important findings. The secondary forest is more homogeneous and uniform, while the old-growth forest is very diverse. Biodiversity of the overstorey in the secondary forest is more than the primary. The number of regenerating species in the secondary forest is higher, but other indices are not statistically different between two types. The regeneration distribute regularly on the ground. The secondary forest still has mother trees and sufficient regeneration, so some restoration measures can be applied here. Findings of the study contribute to improve people’s understanding of the structure and the structural changes after harvesting in Kon Ka Kinh national park, Gia Lai. That is a key to have better understandings of the history and values of the forests. These findings and the proposed restoration measures address rescuing degraded forests in Central Highland in particular and Vietnam in general. And further, this is a promising basis for the management and sustainable use of forest resources in the future.
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Liu, Jia. "Heterogeneous Sensor Data based Online Quality Assurance for Advanced Manufacturing using Spatiotemporal Modeling." Diss., Virginia Tech, 2017. http://hdl.handle.net/10919/78722.
Full textAbstract:
Online quality assurance is crucial for elevating product quality and boosting process productivity in advanced manufacturing. However, the inherent complexity of advanced manufacturing, including nonlinear process dynamics, multiple process attributes, and low signal/noise ratio, poses severe challenges for both maintaining stable process operations and establishing efficacious online quality assurance schemes.
To address these challenges, four different advanced manufacturing processes, namely, fused filament fabrication (FFF), binder jetting, chemical mechanical planarization (CMP), and the slicing process in wafer production, are investigated in this dissertation for applications of online quality assurance, with utilization of various sensors, such as thermocouples, infrared temperature sensors, accelerometers, etc. The overarching goal of this dissertation is to develop innovative integrated methodologies tailored for these individual manufacturing processes but addressing their common challenges to achieve satisfying performance in online quality assurance based on heterogeneous sensor data. Specifically, three new methodologies are created and validated using actual sensor data, namely,
(1) Real-time process monitoring methods using Dirichlet process (DP) mixture model for timely detection of process changes and identification of different process states for FFF and CMP. The proposed methodology is capable of tackling non-Gaussian data from heterogeneous sensors in these advanced manufacturing processes for successful online quality assurance.
(2) Spatial Dirichlet process (SDP) for modeling complex multimodal wafer thickness profiles and exploring their clustering effects. The SDP-based statistical control scheme can effectively detect out-of-control wafers and achieve wafer thickness quality assurance for the slicing process with high accuracy.
(3) Augmented spatiotemporal log Gaussian Cox process (AST-LGCP) quantifying the spatiotemporal evolution of porosity in binder jetting parts, capable of predicting high-risk areas on consecutive layers. This work fills the long-standing research gap of lacking rigorous layer-wise porosity quantification for parts made by additive manufacturing (AM), and provides the basis for facilitating corrective actions for product quality improvements in a prognostic way.
These developed methodologies surmount some common challenges of advanced manufacturing which paralyze traditional methods in online quality assurance, and embody key components for implementing effective online quality assurance with various sensor data. There is a promising potential to extend them to other manufacturing processes in the future.<br>Ph. D.
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Penot, David. "Cartographie des événements hydrologiques extrêmes et estimation SCHADEX en sites non jaugés." Thesis, Grenoble, 2014. http://www.theses.fr/2014GRENU022/document.
Full textAbstract:
Depuis 2006, à EDF, les études de crues extrêmes sont réalisées avec la méthode SCHADEX (Simulation Climato-Hydrologique pour l'Appréciation des Débits EXtrêmes). Elle s'appuie sur un modèle probabiliste MEWP (distribution saisonnière utilisant une classification par type de temps) pour décrire l'aléa pluie et sur une simulation stochastique croisant l'aléa pluie et l'aléa de saturation du bassin. Les approches par simulation, type SCHADEX, ont montré de bonnes performances pour estimer les distributions de crues extrêmes (projet ANR ExtraFlo , 2013). Cependant, l'utilisation de SCHADEX en l'absence de données (pluie, température, débit) sur le bassin à étudier reste problématique. Cette thèse propose une adaptation de la méthode en site non jaugé en essayant de conserver ses points forts, à savoir: - une structuration spatiale et probabiliste des précipitations conditionnée par les types de temps. - un croisement des aléas pluie et saturation du bassin par simulation stochastique. Ce travail s'est limité au pas de temps journalier afin d'aborder la problématique de régionalisation avec un maximum de données. La démarche s'est alors articulée autour de quatre grands axes: - proposer une méthode de régionalisation des précipitations journalières extrêmes ponctuelles et construire des cartes de pluies aux temps de retour remarquables. Évaluer l'intérêt d'une classification par type de temps pour la régionalisation des distributions de pluies extrêmes et qualifier l'interpolateur de pluie SPAZM pour l'estimation des pluies extrêmes. - s'intéresser à la construction de pluies de bassin (ou pluies spatiales) et en particulier à l'impact des choix de construction de cette pluie sur l'estimation des précipitations extrêmes concernant le bassin. - développer une méthode de simulation stochastique régionale permettant de proposer une distribution de débits journaliers issue d'un croisement des aléas pluies et saturation du bassin. - étudier le passage de la distribution des débits journaliers à la distribution des débits de pointe. Les principaux apports de cette thèse sont les suivants: - la prise en compte des types de temps permet d'améliorer la description des structures spatiales des précipitations extrêmes. - l'information apportée par les pluies SPAZM se révèle être précieuse pour l'estimation des pluies extrêmes en site non jaugé. - une étude de sensibilité du calcul de la pluie spatiale en fonction du nombre de postes utilisés (comparaison des pluies SPAZM et Thiessen) donne une indication sur le biais d'estimation. - le générateur de champs de pluie par bandes tournantes SAMPO permet d'étudier l'abattement sur les précipitations extrêmes et de mettre en place un modèle de correction pour les quantiles élevés des pluies spatiales SPAZM. - une nouvelle méthode de simulation stochastique peu paramétrée mais analogue à la méthode SCHADEX (croisement d'un aléa pluie et d'un aléa de saturation du bassin pour produire une distribution des débits journaliers) est proposée pour l'estimation en site non jaugé. - enfin, un travail préliminaire donne des premiers éléments sur le passage à la distribution des débits de pointe par un générateur d'hydrogrammes s'adaptant à la séquence des débits journaliers simulés. Tous ces développements et conclusions sont détaillés et justifiés dans le mémoire de thèse<br>Since 2006, at EDF, extreme flood estimations are computed with the SCHADEX method (Climatic-hydrological simulation of extreme floods). This method relies on a MEWP probabilistic model (seasonal rainfall distribution using a weather pattern concept) and on a stochastic simulation to cross rainy events hazard and catchment saturation states. Simulation approaches, as SCHADEX, have shown good performances to estimate extreme flood distributions. However, the use of SCHADEX method without data for a considered catchment (rain, temperature, runoff) remains a main issue. This thesis suggests an adaptation of the method in ungauged context, trying to keep the key points of the SCHADEX method: - spatial and probabilistic structure of rainfall conditioned by weather patterns. - a cross of rainfall and catchment saturation hazards by stochastic simulation. This work is limited to a daily step to address the issue of regionalization with a maximum of data. The approach is then structured around four main points: - regionalize punctual daily extreme precipitations and construct maps of return period rainfalls. Evaluate the contribution of a weather type classification for the regionalization of extreme rainfall distributions and qualify the SPAZM interpolator for the estimation of extreme rainfall. - wonder about the construction of an areal rainfall and in particular about the impact of its construction choices on the estimation of extreme precipitations. - develop a regional stochastic simulation method to estimate a distribution of daily runoffs which crosses rainy events and catchment saturation hazards. - study the transposition from a daily runoff distribution to a peak flow distribution. The main contributions of this thesis are: - taking into account the weather types improves the description of spatial patterns of extreme precipitations. - information provided by the SPAZM rainfall interpolator proves to be valuable for the estimation of extreme rainfall in ungauged site. - a sensitivity analysis of the calculation of the areal rainfall based on the number of stations used (comparison SPAZM and Thiessen areal rainfalls) gives an indication of the estimation bias. - the SAMPO rainfall generator used to study the areal reduction factor of extreme precipitation and implement a correction model for high quantiles of SPAZM areal rainfall. - a simplified method of stochastic simulation similar to SCHADEX method (cross between a rainfall hazard and a catchment saturation hazard) is developed to produce a distribution of daily flows in ungauged site. - finally, preliminary work provides a way for the transition to the peak flow distribution using a hydrograph generator adapted to the sequence of daily simulated runoffs. All these developments and conclusions are detailed and justified in the thesis.STAR
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Cyganski, Rita. "Was zieht uns an? Empirische Grundlagen für eine verbesserte Abbildung der Einkaufszielwahl in Verkehrsnachfragemodellen." Doctoral thesis, Humboldt-Universität zu Berlin, 2020. http://dx.doi.org/10.18452/22101.
Full textAbstract:
Eine große Herausforderung für Verkehrsmodelle stellt die korrekte Abbildung der Entscheidungsmuster bei der Zielwahl dar. Diese bestimmt die räumlichen Strukturen der Nachfrage und steht in engem Zusammenhang mit zentralen Ergebnissen der Nachfragemodellierung.
Rund ein Drittel der Alltagswege in Deutschland sind Einkaufs- und Erledigungwege. Zahlreiche Arbeiten zeigen die Bedeutung von habitualisierten Verhaltensmustern bei der Wahl eines Einkaufsortes. Die Motive der Geschäftswahl gelten als sehr vielfältig. Besondere Bedeutung wird zudem den Primäraktivitätenorten zugeschrieben. Gleichwohl erfolgt die Abbildung der Zielwahl in der Nachfragemodellierung zumeist sehr vereinfachend. Gewöhnlich wird von einem Versorgungseinkauf mit der Geschäftsgröße und der Anreisezeit ausgegangen.
Diese Arbeit zeigt anhand empirischer Auswertungen Möglichkeiten einer verhaltensorientierten Abbildung der Einkaufszielwahl in mikroskopischen Personenverkehrsmodellen auf. Im Fokus stehen die Variabilität der Geschäftswahl, die ausschlaggebenden Motive sowie die räumlichen Bezugspunkte der Suche. Am Beispiel des Erwerbs von Nahrungs- und Genussmitteln, von Textilien sowie von Unterhaltungselektronik werden Unterschiede zwischen Einkaufswaren verschiedener Fristigkeit, aber auch zwischen verschiedenen Personengruppen herausgearbeitet.
Simulationsrechnungen mit dem Nachfragemodell TAPAS zeigen, dass eine Differenzierung der Einkaufsart sowie die Nutzung eines motivgestützen Erreichbarkeitsmaßes die Modellierungsergebnisse stark verbessern. Die Arbeit stellt erweiterte Indikatoren für eine Berücksichtigung der räumlichen Bezugspunkte bei der Beurteilung der Modellierungsergebnisse bereit. Auch stehen mit den Analysen der Aktivitätenräume, der Umwegfaktoren, der Lage der Einkaufsorte sowie der kumulierten Reiseweiten Informationen zur Verfügung, die generell für die Definition adäquater Suchräume und Bezugspunkte für die Modellierung städtischer Untersuchungsgebiete genutzt werden können.<br>A major challenge in travel demand modelling is the correct representation of decision patterns underlying the choice of destinations. This choice determines the spatial structures of demand and is closely related to central modelling results.
Around one third of everyday trips in Germany are for shopping and errands. Numerous studies show the importance of habitualised behavioral patterns when choosing a shopping location. The motives for choosing a shop are considered to be very diverse. Particular importance is attributed to primary activity locations. Nevertheless, the representation of the target choice in demand modelling is usually very simplified. Usually, a supply purchase is implicitly assumed, with the size of the shop and travel time from the previous location being the most important choice criteria.
Using empirical analyses, this dissertation shows possibilities for a behavior-oriented depiction of shopping location choice in microscopic passenger transport models. These are discussed in terms of their usability for modeling. The analyses focus on the variability of destinations, the decisive motives and the spatial reference points of the location search. Using the example of the purchase of food and beverages, textiles and consumer electronics, differences between shopping goods of different periodicity and also different groups of people are presented.
Simulation calculations with the demand model TAPAS show that a differentiation of the type of purchase and the use of a motive-based accessibility measure greatly improves the modelling results. The dissertation provides extended indicators for a consideration of spatial reference points in the evaluation of the modelling results. Furthermore, the analyses of activity areas, diversion factors, the location of shopping locations and cumulative travel distances provide information that can be generally used to define adequate search areas and reference points for the modelling of urban study areas.Einkaufsverhalten
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Hunter, Brandon. "Channel Probing for an Indoor Wireless Communications Channel." BYU ScholarsArchive, 2003. https://scholarsarchive.byu.edu/etd/64.
Full textAbstract:
The statistics of the amplitude, time and angle of arrival of multipaths in an indoor environment are all necessary components of multipath models used to simulate the performance of spatial diversity in receive antenna configurations. The model presented by Saleh and Valenzuela, was added to by Spencer et. al., and included all three of these parameters for a 7 GHz channel. A system was built to measure these multipath parameters at 2.4 GHz for multiple locations in an indoor environment. Another system was built to measure the angle of transmission for a 6 GHz channel. The addition of this parameter allows spatial diversity at the transmitter along with the receiver to be simulated. The process of going from raw measurement data to discrete arrivals and then to clustered arrivals is analyzed. Many possible errors associated with discrete arrival processing are discussed along with possible solutions. Four clustering methods are compared and their relative strengths and weaknesses are pointed out. The effects that errors in the clustering process have on parameter estimation and model performance are also simulated.
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Leininger, Thomas Jeffrey. "Bayesian Analysis of Spatial Point Patterns." Diss., 2014. http://hdl.handle.net/10161/8730.
Full textAbstract:
<p>We explore the posterior inference available for Bayesian spatial point process models. In the literature, discussion of such models is usually focused on model fitting and rejecting complete spatial randomness, with model diagnostics and posterior inference often left as an afterthought. Posterior predictive point patterns are shown to be useful in performing model diagnostics and model selection, as well as providing a wide array of posterior model summaries. We prescribe Bayesian residuals and methods for cross-validation and model selection for Poisson processes, log-Gaussian Cox processes, Gibbs processes, and cluster processes. These novel approaches are demonstrated using existing datasets and simulation studies.</p><br>Dissertation
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Moradi, Mohammad Mehdi. "Spatial and spatio-temporal point patterns on linear networks." Doctoral thesis, 2018. http://hdl.handle.net/10362/56711.
Full textAbstract:
A thesis submitted in partial fulfillment of the requirements for the degree of Doctor in Information Management, specialization in Geographic Information Systems<br>The last decade witnessed an extraordinary increase in interest in the analysis
of network related data and trajectories. This pervasive interest is partly caused
by a strongly expanded availability of such datasets. In the spatial statistics field,
there are numerous real examples such as the locations of traffic accidents and
geo-coded locations of crimes in the streets of cities that need to restrict the
support of the underlying process over such linear networks to set and define a
more realistic scenario. Examples of trajectories are the path taken by moving
objects such as taxis, human beings, animals, etc.
Intensity estimation on a network of lines, such as a road network, seems to
be a surprisingly complicated task. Several techniques published in the literature,
in geography and computer science, have turned out to be erroneous. We
propose several adaptive and non-adaptive intensity estimators, based on kernel
smoothing and Voronoi tessellation. Theoretical properties such as bias, variance,
asymptotics, bandwidth selection, variance estimation, relative risk estimation,
and adaptive smoothing are discussed. Moreover, their statistical performance is
studied through simulation studies and is compared with existing methods.
Adding the temporal component, we also consider spatio-temporal point patterns
with spatial locations restricted to a linear network. We present a nonparametric
kernel-based intensity estimator and develop second-order characteristics
of spatio-temporal point processes on linear networks such as K-function
and pair correlation function to analyse the type of interaction between points.
In terms of trajectories, we introduce the R package trajectories that contains
different classes and methods to handle, summarise and analyse trajectory data.
Simulation and model fitting, intensity estimation, distance analysis, movement
smoothing, Chi maps and second-order summary statistics are discussed. Moreover, we analyse different real datasets such as a crime data from Chicago
(US), anti-social behaviour in Castell´on (Spain), traffic accidents in Medell´ın
(Colombia), traffic accidents in Western Australia, motor vehicle traffic accidents
in an area of Houston (US), locations of pine saplings in a Finnish forest, traffic
accidents in Eastbourne (UK) and one week taxi movements in Beijing (China).
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Haltigin, Tim. "Interpreting polygonal terrain network arrangements on Earth and Mars using spatial point patterns." 2010. http://digitool.Library.McGill.CA:8881/R/?func=dbin-jump-full&object_id=92211.
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CHAKRABORTY, AVISHEK. "Modeling Point Patterns, Measurement Error and Abundance for Exploring Species Distributions." Diss., 2010. http://hdl.handle.net/10161/3052.
Full textAbstract:
<p>This dissertation focuses on solving some common problems associated with ecological field studies. In the core of the statistical methodology, lies spatial modeling that provides greater flexibility and improved predictive performance over existing algorithms. The applications involve prevalence datasets for hundreds of plants over a large area in the Cape Floristic Region (CFR) of South Africa.</p><p>In Chapter 2, we begin with modeling the categorical abundance data with a multi level spatial model using background information such as environmental and soil-type factors. The empirical pattern is formulated as a degraded version of the potential pattern, with the degradation effect accomplished in two stages. First, we adjust for land use transformation and then we adjust for measurement error, hence misclassification error, to yield the observed abundance classifications. With data on a regular grid over CFR, the analysis is done with a conditionally autoregressive prior on spatial random effects. With around ~ 37000 cells to work with, a novel paralleilization algorithm is developed for updating the spatial parameters to efficiently estimate potential and transformed abundance surfaces over the entire region.</p><p>In Chapter 3, we focus on a different but increasingly common type of prevalence data in the so called <italic>presence-only</italic> setting. We detail the limitations associated with a usual presence-absence analysis for this data and advocate modeling the data as a point pattern realization. The underlying intensity surface is modeled with a point-level spatial Gaussian process prior, after taking into account sampling bias and change in land-use pattern. The large size of the region enforces using an computational approximation with a bias-corrected predictive process. We compare our methodology against the the most commonly used maximum entropy method, to highlight the improvement in predictive performance.</p><p>In Chapter 4, we develop a novel hierarchical model for analyzing noisy point pattern datasets, that arise commonly in ecological surveys due to multiple sources of bias, as discussed in previous chapters. The effect of the noise leads to displacements of locations as well as potential loss of points inside a bounded domain. Depending on the assumption on existence of locations outside the boundary, a couple of different models -- <italic>island</italic> and <italic>subregion</italic>, are specified. The methodology assumes informative knowledge of the scale of measurement error, either pre-specified or learned from a training sample. Its performance is tested against different scales of measurement error related to the data collection techniques in CFR.</p><p>In Chapter 5, we suggest an alternative model for prevalence data, different from the one in Chapter 3, to avoid numerical approximation and subsequent computational complexities for a large region. A mixture model, similar to the one in Chapter 4 is used, with potential dependence among the weights and locations of components. The covariates as well as a spatial process are used to model the dependence. A novel birth-death algorithm for the number of components in the mixture is under construction.</p><p>Lastly, in Chapter 6, we proceed to joint modeling of multiple-species datasets. The challenge is to infer about inter-species competition with a large number of populations, possibly running into several hundreds. Our contribution involves applying hierarchical Dirichlet process to cluster the presence localities and subsequently developing measures of range overlap from posterior draws. This kind of simultaneous inference can potentially have implications for questions related to biodiversity and conservation studies. .</p><br>Dissertation
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Ashiq, Muhammad Waseem. "Ontario boreal fire regimes in the context of lightning-caused ignition point spatial patterns." Thesis, 2011. http://hdl.handle.net/10012/6257.
Full textAbstract:
Lightning-caused forest fires are one of the major natural disturbances in Ontario managed boreal forests. Survival of these forests with fires for centuries shows that such disturbances are integral to the boreal ecosystem and its ecological functioning. Characterizing the fire regimes defined by fire ignition frequency, fire sizes and their spatial distribution patterns etc. thus can help to improve our understanding of the boreal forest dynamics and provide guidance for management practices attempting to maintain biodiversity and achieve sustainability.
In this thesis the lightning-caused fire ignitions data for four ecoregions in Ontario managed boreal forests (3E, 3W, 3S and 4S) for 1960–2009 were analyzed using pattern analysis and density estimation to determine the spatial nature of fire ignitions. These fire ignition spatial patterns were further used (as weighted ignition scenario) to simulate forest fire regimes in the study area. Fire regimes were also simulated using spatially unweighted ignitions (unweighted ignition scenario). Non-spatial (total number of fires, total burn area, number of fires by size classes, annual burn fraction) and spatial (spatial burn probability) indicators of the simulated fire regimes under both ignition scenarios were compared to test the null hypothesis that modeled forest fire regime is not affected by the spatial patterns of input fire ignitions. All data analysis were performed for individual ecoregions. Spatial pattern of ignitions were analyzed using the nearest neighbour index and Ripley’s K-function. Ignition densities were estimated using the adaptive kernel density estimation method and the fire regimes were simulated using BFOLDS (Boreal Forests Landscape Dynamics Simulator).
Results showed that lightning-caused fire ignitions are clustered in all ecoregions. Fire ignition density also varied spatially within ecoregions. Overall fire ignition density was highest in the northwestern ecoregion (4S) and lowest in the eastern ecoregion (3E), which corresponds to the combined gradient of effective humidity and temperature in Ontario. For each ecoregion, comparison of non-spatial simulated fire regime indicators showed statistically non-significant differences between unweighted and weighted ignitions. The spatial burn probability however captured clear spatial differences between unweighted and weighted ignitions. Spatial differences in spatial burn probability between both ignition scenarios were more prominent in ecoregions of high fire occurrence. Results of the weighted ignition scenario closely followed the spatial patterns of the estimated fire ignition density in the study area. Based on these results this thesis rejects the null hypothesis and emphasizes that ignition patterns must be considered in simulating fire regime in Ontario boreal forests.