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Using virtual reality and percolation theory to visualize fluid flow in porous media / Carlos Magno De Lima in Geoinformatica, vol 17 n° 4 (October 2013)  

Public [article]  inGeoinformatica > vol 17 n° 4 (October 2013) . - pp 521 - 541 Titre : Using virtual reality and percolation theory to visualize fluid flow in porous media Type de document : Article/Communication Auteurs : Carlos Magno De Lima, Auteur ; Luis M. G. Gonçalves, Auteur ; Cristiana Bentes, Auteur ; Ricardo Farias, Auteur Année de publication : 2013 Article en page(s) : pp 521 - 541 Note générale : Bibliographie Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Géomatique [Termes IGN] analyse visuelle [Termes IGN] données localisées 3D [Termes IGN] dynamique des fluides [Termes IGN] flux de données [Termes IGN] modèle de simulation [Termes IGN] prospection pétrolière [Termes IGN] réalité virtuelle [Termes IGN] visualisation 3D Résumé : (Auteur) The study of the fluid flow process through porous media can bring valuable contributions in areas like oil exploration and environmental research. In this work, we propose an interactive tool, named VRFluid, that allows visual interpretation of the three-dimensional data generated by the simulation of the fluid flow the porous media. VRFluid comprises a virtual reality engine that provides stereo visualization of the three-dimensional data, and a simulation engine based on a dynamic percolation method to model the fluid flow. VRFluid is composed of two independent main threads, the percolation simulator and the rendering server, that can operate in parallel as a pipeline. We tested our tool on a region of a mature field database, supervised by geophysicists, and obtained images of the interior of the percolation data, providing important results for the interpretation and cluster formation process. Numéro de notice : A2013-508 Affiliation des auteurs : non IGN Thématique : GEOMATIQUE Nature : Article DOI : 10.1007/s10707-012-0168-5 Date de publication en ligne : 23/10/2012 En ligne : https://doi.org/10.1007/s10707-012-0168-5 Format de la ressource électronique : URL article Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=32646 [article]

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The k closest pairs in spatial databases: When only set is indexed / Gilberto Gutiérrez in Geoinformatica, vol 17 n° 4 (October 2013)  

Public [article]  inGeoinformatica > vol 17 n° 4 (October 2013) . - pp 543 - 565 Titre : The k closest pairs in spatial databases: When only set is indexed Type de document : Article/Communication Auteurs : Gilberto Gutiérrez, Auteur ; Pablo Saez, Auteur Année de publication : 2013 Article en page(s) : pp 543 - 565 Note générale : Bibliographie Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Bases de données localisées [Termes IGN] arbre-R [Termes IGN] base de données localisées [Termes IGN] extensibilité [Termes IGN] rectangle englobant minimum [Termes IGN] requête spatiale Résumé : (Auteur) We provide in this article a branch-and-bound algorithm that solves the problem of finding the k closest pairs of points (p,q), p € P,q € Q, considering two sets of points in the euclidean plane P,Q stored in external memory assuming that only one of the sets has a spatial index. This problem arises naturally in many scenarios, for instance when the set without an index is the answer to a spatial query. The main idea of our algorithm is to partition the space occupied by the set without an index into several cells or subspaces and to make use of the properties of a set of metrics defined on two Minimum Bounding Rectangles (MBRs). We evaluated our algorithm for different values of k by means of a series of experiments that considered both synthetical and real world datasets. We compared the performance of our algorithm with that of techniques that either assume that both datasets have a spatial index or that none has an index. The results show that our algorithm needs only between a 0.3 and a 35 % of the disk accesses required by such techniques. Our algorithm also shows a good scalability, both in terms of k and of the size of the data set. Numéro de notice : A2013-509 Affiliation des auteurs : non IGN Thématique : GEOMATIQUE/INFORMATIQUE Nature : Article DOI : 10.1007/s10707-012-0169-4 Date de publication en ligne : 14/09/2012 En ligne : https://doi.org/10.1007/s10707-012-0169-4 Format de la ressource électronique : URL article Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=32647 [article]

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Opportunistic sampling-based query processing in wireless sensor networks / Muhammad Umer in Geoinformatica, vol 17 n° 4 (October 2013)  

Public [article]  inGeoinformatica > vol 17 n° 4 (October 2013) . - pp 567 - 597 Titre : Opportunistic sampling-based query processing in wireless sensor networks Type de document : Article/Communication Auteurs : Muhammad Umer, Auteur ; Egemen Tanin, Auteur ; Lars Kulik, Auteur Année de publication : 2013 Article en page(s) : pp 567 - 597 Note générale : Bibliographie Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Géomatique [Termes IGN] modélisation spatio-temporelle [Termes IGN] requête (informatique) [Termes IGN] réseau de capteurs [Termes IGN] télécommunication sans fil [Termes IGN] transmission de données Résumé : (Auteur) High resolution sampling of physical phenomenon is a prime application of large scale wireless sensor networks (WSNs). With hundreds of nodes deployed over vast tracts of land, monitoring data can now be generated at unprecedented spatio-temporal scales. However, the limited battery life of individual nodes in the network mandates smart ways of collecting this data by maximizing localized processing of information at the node level. In this paper, we propose a WSN query processing method that enhances localized information processing by harnessing the two inherent aspects of WSN communication, i.e., multihop and multipath data transmission. In an active WSN where data collection queries are regularly processed, multihop and multipath routing leads to a situation where a significant proportion of nodes relay and overhear data generated by other nodes in the network. We propose that nodes opportunistically sample this data as they communicate. We model the data communication process in a WSN and show that opportunistic sampling during data communication leads to surprisingly accurate global knowledge at each node. We present an opportunistic query processing system that uses the accumulated global knowledge to limit the data collection requirements for future queries while ensuring temporal freshness of the results. Numéro de notice : A2013-510 Affiliation des auteurs : non IGN Thématique : GEOMATIQUE/SOCIETE NUMERIQUE Nature : Article DOI : 10.1007/s10707-012-0170-y Date de publication en ligne : 05/10/2012 En ligne : https://doi.org/10.1007/s10707-012-0170-y Format de la ressource électronique : URL article Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=32648 [article]

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Blind evaluation of location based queries using space transformation to preserve location privacy / Ali Khshgozaran in Geoinformatica, vol 17 n° 4 (October 2013)  

Public [article]  inGeoinformatica > vol 17 n° 4 (October 2013) . - pp 599 - 634 Titre : Blind evaluation of location based queries using space transformation to preserve location privacy Type de document : Article/Communication Auteurs : Ali Khshgozaran, Auteur ; Houtan Shirani-Mehr, Auteur ; Cyrus Shahabi, Auteur Année de publication : 2013 Article en page(s) : pp 599 - 634 Note générale : Bibliographie Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Analyse spatiale [Termes IGN] espace de Hilbert [Termes IGN] géopositionnement [Termes IGN] plus proche voisin, algorithme du [Termes IGN] protection de la vie privée [Termes IGN] requête spatiale [Termes IGN] service fondé sur la position [Termes IGN] utilisateur Résumé : (Auteur) In this paper, we propose a fundamental approach to perform the class of Range and Nearest Neighbor (NN) queries, the core class of spatial queries used in location-based services, without revealing any location information about the query in order to preserve users’ private location information. The idea behind our approach is to utilize the power of one-way transformations to map the space of all objects and queries to another space and resolve spatial queries blindly in the transformed space. Traditional encryption based techniques, solutions based on the theory of private information retrieval, or the recently proposed anonymity and cloaking based approaches cannot provide stringent privacy guarantees without incurring costly computation and/or communication overhead. In contrast, we propose efficient algorithms to evaluate KNN and range queries privately in the Hilbert transformed space. We also propose a dual curve query resolution technique which further reduces the costs of performing range and KNN queries using a single Hilbert curve. We experimentally evaluate the performance of our proposed range and KNN query processing techniques and verify the strong level of privacy achieved with acceptable computation and communication overhead. Numéro de notice : A2013-511 Affiliation des auteurs : non IGN Thématique : GEOMATIQUE Nature : Article DOI : 10.1007/s10707-012-0172-9 Date de publication en ligne : 29/11/2012 En ligne : https://doi.org/10.1007/s10707-012-0172-9 Format de la ressource électronique : URL article Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=32649 [article]

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Decentralized querying of topological relations between regions monitored by a coordinate-free geosensor network / Myeong-Hung Jeong in Geoinformatica, vol 17 n° 4 (October 2013)  

Public [article]  inGeoinformatica > vol 17 n° 4 (October 2013) . - pp 669 - 696 Titre : Decentralized querying of topological relations between regions monitored by a coordinate-free geosensor network Type de document : Article/Communication Auteurs : Myeong-Hung Jeong, Auteur ; Matt Duckham, Auteur Année de publication : 2013 Article en page(s) : pp 669 - 696 Note générale : Bibliographie Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Géomatique [Termes IGN] format SVG [Termes IGN] intersection spatiale [Termes IGN] relation topologique [Termes IGN] requête spatiale [Termes IGN] réseau de capteurs Résumé : (Auteur) Geosensor networks present unique resource constraints to spatial computation, including limited battery power, communication constraints, and frequently a lack of coordinate positioning systems. As a result, there is a need for new algorithms that can efficiently satisfy basic spatial queries within those resource constraints. This paper explores the design and evaluation of a family of new algorithms for determining the topological relations between regions monitored by such a resource-constrained geosensor network. The algorithms are based on efficient, decentralized (in-network) variants of conventional 4-intersection and intersection and difference models, with in-network data aggregation. Further, our algorithms operate without any coordinate information, making them suitable applications where a positioning system is unavailable or unreliable. While all four algorithms are shown to have overall communication complexity O(n) and optimal load balance O(1), the algorithms differ in the level of topological detail they can detect; the types of regions they can monitor; and in the constant factors for communication complexity. The paper also demonstrates the impact of finite granularity observations on the correctness of the query results. In the conclusions, we identify the need to conduct further fundamental research on the relationship between topological relations between regions and limited granularity sensor observations of those regions. Numéro de notice : A2013-513 Affiliation des auteurs : non IGN Thématique : GEOMATIQUE/SOCIETE NUMERIQUE Nature : Article DOI : 10.1007/s10707-012-0172-9 Date de publication en ligne : 03/02/2013 En ligne : https://doi.org/10.1007/s10707-012-0172-9 Format de la ressource électronique : URL article Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=32650 [article]

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