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Algorithms for constrained k-nearest neighbor queries over moving object trajectories / Yunjun Gao in Geoinformatica, vol 14 n° 2 (April 2010)  

Public [article]  inGeoinformatica > vol 14 n° 2 (April 2010) . - pp 241 - 276 Titre : Algorithms for constrained k-nearest neighbor queries over moving object trajectories Type de document : Article/Communication Auteurs : Yunjun Gao, Auteur ; B. Zheng, Auteur ; G. Chen, Auteur ; Qi Li, Auteur Année de publication : 2010 Article en page(s) : pp 241 - 276 Note générale : Bibliographie Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Bases de données localisées [Termes IGN] arbre-R [Termes IGN] base de données d'objets mobiles [Termes IGN] base de données spatiotemporelles [Termes IGN] classification barycentrique [Termes IGN] objet mobile [Termes IGN] processus spatial [Termes IGN] programmation par contraintes [Termes IGN] requête spatiale Résumé : (Auteur) An important query for spatio-temporal databases is to find nearest trajectories of moving objects. Existing work on this topic focuses on the closest trajectories in the whole data space. In this paper, we introduce and solve constrained k-nearest neighbor (CkNN) queries and historical continuous CkNN (HCCkNN) queries on R-tree-like structures storing historical information about moving object trajectories. Given a trajectory set D, a query object (point or trajectory) q, a temporal extent T, and a constrained region CR, (i) a CkNN query over trajectories retrieves from D within T, the k (? 1) trajectories that lie closest to q and intersect (or are enclosed by) CR; and (ii) an HCCkNN query on trajectories retrieves the constrained k nearest neighbors (CkNNs) of q at any time instance of T. We propose a suite of algorithms for processing CkNN queries and HCCkNN queries respectively, with different properties and advantages. In particular, we thoroughly investigate two types of CkNN queries, i.e., CkNNP and CkNNT, which are defined with respect to stationary query points and moving query trajectories, respectively; and two types of HCCkNN queries, namely, HCCkNNP and HCCkNNT, which are continuous counterparts of CkNNP and CkNNT, respectively. Our methods utilize an existing data-partitioning index for trajectory data (i.e., TB-tree) to achieve low I/O and CPU cost. Extensive experiments with both real and synthetic datasets demonstrate the performance of the proposed algorithms in terms of efficiency and scalability. Copyright Springer Numéro de notice : A2010-067 Affiliation des auteurs : non IGN Thématique : GEOMATIQUE/INFORMATIQUE Nature : Article DOI : 10.1007/s10707-009-0084-5 Date de publication en ligne : 28/04/2009 En ligne : https://doi.org/10.1007/s10707-009-0084-5 Format de la ressource électronique : URL article Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=30263 [article]

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Global structure of marine wind speed variability derived from Topex altimeter data / G. Chen in International Journal of Remote Sensing IJRS, vol 24 n° 24 (December 2003)  

Public [article]  inInternational Journal of Remote Sensing IJRS > vol 24 n° 24 (December 2003) . - pp 5119 - 5133 Titre : Global structure of marine wind speed variability derived from Topex altimeter data Type de document : Article/Communication Auteurs : G. Chen, Auteur ; S.W. Bi, Auteur ; J. Ma, Auteur Année de publication : 2003 Article en page(s) : pp 5119 - 5133 Note générale : Bibliographie Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Traitement d'image [Termes IGN] climat terrestre [Termes IGN] courant aérien [Termes IGN] données altimétriques [Termes IGN] données Topex-Poseidon [Termes IGN] géophysique externe [Termes IGN] océanographie spatiale [Termes IGN] Pacifique (océan) [Termes IGN] surface de la mer [Termes IGN] vague [Termes IGN] vent Résumé : (Auteur) As the largest source of momentum for the ocean surface, wind affects the full range, of oceanic motion-from individual surface waves to complete current systems. The marine surface wind is among the critical geophysical parameters which determine the most fundamental aspects of the ocean. Using six years (1993-1998) of TOPEX altimeter data with an unprecedented accuracy and continuity, a detailed investigation of the global structure of marine wind climatology and variability is carried out. It is found that the overall pattern of wind climatology is basically determined by solar radiation and therefore dominated by zonal features, while that of the wind variability is largely 'event' determined and thereby dominated by regional features. Consequently, wind climatology and wind variability show a complex relationship in their magnitude of intensity. Strong winds may be associated with high variabilities, such as in the westerlies of the North Atlantic and North Pacific; they may also be associated with low variabilities, such as in the westerlies of the Southern Ocean. Meanwhile, weak wind zones like the doldrums in the western equatorial Pacific can have a very low level of annual variability, while a very high level of interannual variability. The Asian monsoon system has a lower than average climatological mean speed, but exhibits extremely high annual variability. The phase distributions of wind variations carry combined information of climatology and variability. Effects of the Asian monsoon and marine storms are manifested on top of the basically zonal phase pattern. Statistics suggest that semiannual variability exceeds annual variability for 12.2% of the world's oceans, and interannual variability exceeds annual variability for 26.4% of the world's oceans. Numéro de notice : A2003-340 Affiliation des auteurs : non IGN Thématique : IMAGERIE Nature : Article nature-HAL : ArtAvecCL-RevueIntern DOI : 10.1080/0143116031000082091 En ligne : https://doi.org/10.1080/0143116031000082091 Format de la ressource électronique : URL article Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=22635 [article]

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