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A conceptual density-based approach for the disambiguation of toponyms / D. Buscaldi in International journal of geographical information science IJGIS, vol 22 n° 3 (march 2008)
[article]
Titre : A conceptual density-based approach for the disambiguation of toponyms Type de document : Article/Communication Auteurs : D. Buscaldi, Auteur ; P. Rosso, Auteur Année de publication : 2008 Article en page(s) : pp 301 - 313 Note générale : Bibliographie Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Infrastructure de données
[Termes IGN] géomatique web
[Termes IGN] indexation spatiale
[Termes IGN] recherche d'information géographique
[Termes IGN] résolution d'ambiguïté
[Termes IGN] toponymeRésumé : (Auteur) Nowadays, a huge quantity of information is stored in digital format. A great portion of this information is constituted by textual and unstructured documents, where geographical references are usually given by means of place names. A common problem with textual information retrieval is represented by polysemous words, that is, words can have more than one sense. This problem is present also in the geographical domain: place names may refer to different locations in the world. In this paper we investigate the use of our word sense disambiguation technique in the geographical domain, with the aim of resolving ambiguous place names. Our technique is based on WordNet conceptual density. Due to the lack of a reference corpus tagged with WordNet senses, we carried out the experiments over a set of 1,210 place names extracted from the SemCor corpus that we named GeoSemCor and made publicly available. We compared our method with the most-frequent baseline and the enhanced-Lesk method, which previously has not been tested in large contexts. The results show that a better precision can be achieved by using a small context (phrase level), whereas a greater coverage can be obtained by using large contexts (document level). The proposed method should be tested with other corpora, due to the fact that our experiments evidenced the excessive bias towards the most-frequent sense of the GeoSemCor. Copyright Taylor & Francis Numéro de notice : A2008-141 Affiliation des auteurs : non IGN Thématique : GEOMATIQUE Nature : Article DOI : 10.1080/13658810701626251 En ligne : https://doi.org/10.1080/13658810701626251 Format de la ressource électronique : URL article Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=29136
in International journal of geographical information science IJGIS > vol 22 n° 3 (march 2008) . - pp 301 - 313[article]Réservation
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Code-barres Cote Support Localisation Section Disponibilité 079-08021 RAB Revue Centre de documentation En réserve L003 Disponible 079-08022 RAB Revue Centre de documentation En réserve L003 Disponible Fast error analysis of continuous GPS observations / M. Bos in Journal of geodesy, vol 82 n° 3 (March 2008)
[article]
Titre : Fast error analysis of continuous GPS observations Type de document : Article/Communication Auteurs : M. Bos, Auteur ; R. Fernandes, Auteur ; S. Williams, Auteur ; et al., Auteur Année de publication : 2008 Article en page(s) : pp 157 - 166 Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Géodésie spatiale
[Termes IGN] bruit blanc
[Termes IGN] classification par maximum de vraisemblance
[Termes IGN] données GPS
[Termes IGN] incertitude des données
[Termes IGN] série temporelleRésumé : (Auteur) It has been generally accepted that the noise in continuous GPS observations can be well described by a power-law plus white noise model. Using maximum likelihood estimation (MLE) the numerical values of the noise model can be estimated. Current methods require calculating the data covariance matrix and inverting it, which is a significant computational burden. Analysing 10 years of daily GPS solutions of a single station can take around 2 h on a regular computer such as a PC with an AMD AthlonTM 64 X2 dual core processor. When one analyses large networks with hundreds of stations or when one analyses hourly instead of daily solutions, the long computation times becomes a problem. In case the signal only contains power-law noise, the MLE computations can be simplified to a O(N log N) process where N is the number of observations. For the general case of power-law plus white noise, we present a modification of the MLE equations that allows us to reduce the number of computations within the algorithm from a cubic to a quadratic function of the number of observations when there are no data gaps. For time-series of three and eight years, this means in practise a reduction factor of around 35 and 84 in computation time without loss of accuracy. In addition, this modification removes the implicit assumption that there is no environment noise before the first observation. Finally, we present an analytical expression for the uncertainty of the estimated trend if the data only contains power-law noise. Copyright Springer Numéro de notice : A2008-167 Affiliation des auteurs : non IGN Thématique : POSITIONNEMENT Nature : Article nature-HAL : ArtAvecCL-RevueIntern DOI : 10.1007/s00190-007-0165-x En ligne : https://doi.org/10.1007/s00190-007-0165-x Format de la ressource électronique : URL article Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=29162
in Journal of geodesy > vol 82 n° 3 (March 2008) . - pp 157 - 166[article]Réservation
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Code-barres Cote Support Localisation Section Disponibilité 266-08031 RAB Revue Centre de documentation En réserve L003 Disponible 266-08032 RAB Revue Centre de documentation En réserve L003 Disponible
[article]
Titre : GNSS indoors : fighting the fading, part 1 Type de document : Article/Communication Auteurs : Günter W. Hein, Auteur ; M. Paonni, Auteur ; V. Kropp, Auteur ; et al., Auteur Année de publication : 2008 Article en page(s) : 10 p. ; pp 43 - 52 Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Navigation et positionnement
[Termes IGN] positionnement en intérieur
[Termes IGN] signal GNSS
[Termes IGN] traitement du signalRésumé : (Editeur) The ability to receive low-power GNSS signals inside buildings represents a veritable Holy Grail for product designers and manufacturers. Despite increases in receiver sensitivity and sophisticated signal-processing techniques, consistent and robust positioning indoors has not been achieved. In this first of a two-part exploration of the subject, the authors review existing models of indoor signal processing and the results of a new test designed to create an original model of satellite-navigation signal behavior as it propagates through diverse room shapes and building materials. Copyright Gibbons Media & Research LLC Numéro de notice : A2008-648 Affiliation des auteurs : non IGN Thématique : POSITIONNEMENT Nature : Article DOI : sans Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=33527
in Inside GNSS > vol 3 n° 2 (March 2008) . - 10 p. ; pp 43 - 52[article]Voir aussiDocuments numériques
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GNSS indoors ... - pdfAdobe Acrobat PDF Improving long-range RTK: getting a better handle on the biases / D. Kim in GPS world, vol 19 n° 3 (March 2008)
[article]
Titre : Improving long-range RTK: getting a better handle on the biases Type de document : Article/Communication Auteurs : D. Kim, Auteur ; R.B. Langley, Auteur Année de publication : 2008 Article en page(s) : pp 50 - 56 Note générale : Bibliographie Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Traitement du signal
[Termes IGN] correction atmosphérique
[Termes IGN] GPS en mode cinématique
[Termes IGN] phase GPS
[Termes IGN] positionnement cinématique en temps réel
[Termes IGN] propagation ionosphérique
[Termes IGN] propagation troposphérique
[Termes IGN] résolution d'ambiguïtéRésumé : (Editeur) Scientists and engineers continue to improve high-accuracy GPS positioning techniques - techniques pioneered a quarter of a century ago. The first GPS satellite, SVN01/PRN04, was launched from Cape Canaveral on February 22, 1978. And between 1978 and 1985, the U.S. Air Force orbited nine more prototype or Block I satellites to test key technologies before deploying the operational constellation. Surveyors and geodesists were among the earliest users of the Block I satellites. Using the satellite signals, they developed accurate positioning techniques based on the use of carrier-phase observations - about two orders of magnitude more precise than code measurements. To reduce the effect of biases and errors in the measurements, they developed the concepts of between-satellite and between-receiver single differencing of the carrier-phase data as well as double and triple differencing. Raw measurements were recorded by receivers and then post-processed to obtain receiver coordinates. Clever approaches were developed to handle the integer ambiguity of the carrier phases. With the launch of the Block II satellites beginning in 1989, further improvements in positioning accuracy and efficiency became possible, including real-time carrier-phase based positioning with a radio link between a reference receiver and a remote receiver. This technique became known as real-time kinematic or RTK, as it permitted the remote receiver to rove and occupy different points in a single positioning exercise. But carrier-phase ambiguity resolution issues coupled with inaccurately modeled satellite orbit and atmospheric effects has limited consistent single-baseline RTK operation between reference and rover receivers to tens of kilometers. On longer baselines, inaccurate modeling can result in significant positioning errors. Network RTK, using simultaneously operating reference stations to better determine error corrections, can extend the area of coverage of RTK but it, too, has limitations. In this month's column, I am joined by my colleague Don Kim who has developed an innovative approach to long-range RTK. We describe how accurate modeling of atmospheric effects coupled with an ionosphere-free ambiguity resolution process results in successful long-range RTK that can be implemented in either single-baseline or network mode. Has the ultimate RTK approach been developed? Probably not. But we're getting closer. Copyright Questex Media Group Inc Numéro de notice : A2008-162 Affiliation des auteurs : non IGN Thématique : IMAGERIE/POSITIONNEMENT Nature : Article DOI : sans Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=29157
in GPS world > vol 19 n° 3 (March 2008) . - pp 50 - 56[article]Réservation
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Code-barres Cote Support Localisation Section Disponibilité 067-08031 RAB Revue Centre de documentation En réserve L003 Disponible On the non-uniqueness of local quasi-geoids computed from terrestrial gravity anomalies / I. Prutkin in Journal of geodesy, vol 82 n° 3 (March 2008)
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Titre : On the non-uniqueness of local quasi-geoids computed from terrestrial gravity anomalies Type de document : Article/Communication Auteurs : I. Prutkin, Auteur ; R. Klees, Auteur Année de publication : 2008 Article en page(s) : pp 147 - 156 Note générale : Bibliographie Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Géodésie physique
[Termes IGN] anomalie de pesanteur
[Termes IGN] champ de pesanteur local
[Termes IGN] données GPS
[Termes IGN] géoïde local
[Termes IGN] nivellement par GPSRésumé : (Auteur) We consider the problem of local (quasi-)geoid modelling from terrestrial gravity anomalies. Whereas this problem is uniquely solvable (up to spherical harmonic degree one) if gravity anomalies are globally available, the problem is non-unique if gravity anomalies are only available within a local area, which is the typical situation in local/regional gravity field modelling. We derive a mathematical description of the kernel of the gravity anomaly operator. The non-uniqueness can be removed using external height anomaly information, e.g., provided by GPS-levelling. The corresponding problem is formulated as a Cauchy problem for the Laplace equation. The existence and uniqueness of the solution of the Cauchy problem is guaranteed by the Cauchy–Kowalevskaya theorem. We propose several numerical procedures to compute the solution of the Cauchy problem from given differences between gravimetric and geometric height anomalies. We apply the numerical techniques to real data over the Netherlands and Germany. We show that we can compute a unique quasi-geoid from observed gravimetric and geometric height anomalies, which agree with the data within the expected noise level. We conclude that observed differences between gravimetric height anomalies and geometric height anomalies derived from GPS and levelling cannot only be attributed to systematic errors in the data sets, but are also caused by the intrinsic non-uniqueness of the problem of local quasi-geoid modelling from gravity anomalies. Hence, GPS-levelling data are necessary to get a unique solution, which also implies that they should not be used to validate local quasi-geoid solutions computed on the basis of gravity anomalies. Copyright Springer Numéro de notice : A2008-166 Affiliation des auteurs : non IGN Thématique : POSITIONNEMENT Nature : Article nature-HAL : ArtAvecCL-RevueIntern DOI : 10.1007/s00190-007-0161-1 En ligne : https://doi.org/10.1007/s00190-007-0161-1 Format de la ressource électronique : URL article Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=29161
in Journal of geodesy > vol 82 n° 3 (March 2008) . - pp 147 - 156[article]Réservation
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Code-barres Cote Support Localisation Section Disponibilité 266-08031 RAB Revue Centre de documentation En réserve L003 Disponible 266-08032 RAB Revue Centre de documentation En réserve L003 Disponible Using co-occurrence models for placename disambiguation / S. Overell in International journal of geographical information science IJGIS, vol 22 n° 3 (march 2008)PermalinkLa via Julia Augusta entre Menton et Nice / Jérôme Repetti in Géomatique expert, n° 61 (01/03/2008)PermalinkGALILEO validation: the validation message / M. Tossaint in GPS world, vol 19 n° 2 (February 2008)PermalinkTsunami detection by GPS: how ionospheric observations might improve the global warning system / Giovanni Occhipinti in GPS world, vol 19 n° 2 (February 2008)PermalinkAssessment of water budgets computed from NWP models and observational datasets during AMMA-EOP / Olivier Bock (2008)PermalinkDéveloppement et validation d'une méthode de calcul GPS intégrant des mesures de profils de vapeur d'eau en visée multi-angulaire pour l'altimétrie de haute précision / Pierre Bosser (2008)PermalinkPermalinkGPS composite clock analysis / James R. Wright in International Journal of Navigation and Observation, vol 2008 (01/01/2008)PermalinkLocal ties, VLBI-GPS eccentricities and combination of geodetic reference frames / Claudio Abbondanza (2008)PermalinkMulti-dimensional B-spline modeling of spatio-temporal Ionospheric signals / C. Zeilhofer (2008)Permalink