Centre de documentation
scientifique

Assessing the quality of GEOID12B model through field surveys / Ahmed F. Elaksher in Journal of applied geodesy, vol 12 n° 1 (January 2018)  

Public [article]  inJournal of applied geodesy > vol 12 n° 1 (January 2018) . - pp 1 - 14 Titre : Assessing the quality of GEOID12B model through field surveys Type de document : Article/Communication Auteurs : Ahmed F. Elaksher, Auteur ; Franck Kamtchang, Auteur ; Christian Wegmann, Auteur ; Adalberto Guerrero, Auteur Année de publication : 2018 Article en page(s) : pp 1 - 14 Note générale : bibliographie Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Géodésie physique [Termes IGN] altitude orthométrique [Termes IGN] anomalie de pesanteur [Termes IGN] Etats-Unis [Termes IGN] géoïde local [Termes IGN] hauteur ellipsoïdale [Termes IGN] quasi-géoïde Résumé : (auteur) Elevation differences have been determined through conventional ground surveying techniques for over a century. Since the mid-80s GPS, GLONASS and other satellite systems have modernized the means by which elevation differences are observed. In this article, we assessed the quality of GEIOD12B through long-occupation GNSS static surveys. A set of NGS benchmarks was occupied for at least one hour using dual-frequency GNSS receivers. Collected measurements were processed using a single CORS station at most 24 kilometers from the benchmarks. Geoid undulation values were driven by subtracting measured ellipsoidal heights from the orthometric heights posted on the NGS website. To assess the quality of GEOID12B, we compared our computed vertical shifts at the benchmarks with those estimated from GEOID12B published by NGS. In addition, Kriging model was used to interpolate local maps for the geoid undulations from the benchmark heights. The maps were compared with corresponding parts of GEOID12B. No biases were detected in the results and only shifts due to random errors were found. Discrepancies in the range of ten centimetres were noticed between our geoid undulation and the values available from NGS. Numéro de notice : A2018-013 Affiliation des auteurs : non IGN Thématique : POSITIONNEMENT Nature : Article DOI : 10.1515/jag-2017-0013 En ligne : https://doi.org/10.1515/jag-2017-0013 Format de la ressource électronique : URL article Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=89092 [article]

Evaluating the use of GPS heights in water conservation applications / Ahmed F. Elaksher in Survey review, vol 48 n° 348 (May 2016)  

Public [article]  inSurvey review > vol 48 n° 348 (May 2016) . - pp 195 - 201 Titre : Evaluating the use of GPS heights in water conservation applications Type de document : Article/Communication Auteurs : Ahmed F. Elaksher, Auteur ; A. Fernald, Auteur ; F. Kapoko, Auteur Année de publication : 2016 Article en page(s) : pp 195 - 201 Note générale : bibliographie Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Topographie [Termes IGN] altitude orthométrique [Termes IGN] analyse comparative [Termes IGN] GPS en mode statique [Termes IGN] hauteur ellipsoïdale [Termes IGN] niveau de l'eau [Termes IGN] nivellement indirect [Termes IGN] Nouveau-Mexique (Etats-Unis) [Termes IGN] positionnement par GPS [Termes IGN] positionnement statique rapide [Termes IGN] récepteur GPS [Termes IGN] station de contrôle [Termes IGN] station de référence Résumé : (auteur) Accurate water level elevations are imperative for water resource management. This paper presents the outcomes of a research study using GPS in measuring water level heights. The authors observed the water elevations of several wells, United States Geological Survey (USGS) gauges and acequia points at three different locations in North–Central New Mexico, USA. Different rapid static and static observation sessions were collected independently and adjusted using the nearby reference control stations. The authors used two different sets of receivers: four Topcon Hiper Lite+ and two Leica GPS1200 The authors were able to examine several network configurations with different continuously operating reference station (CORS) stations. Our findings were analogous to empirically expected errors and showed insignificant differences among the heights obtained from rapid static and static sessions at a 95% confidence level. The authors also compared the results with National Geodetic Survey online positioning users service (NGS OPUS) solutions and confirmed the accuracy of our measurements. As independent measurement technique, we measured the height differences among several of these points with conventional levelling surveys. Our GPS measurements provided small disagreements with height differences obtained with the terrestrial surveys, after the GPS heights were reduced to their orthometric correspondences. Based on these findings, current rapid static GPS positioning methodologies are capable of providing equivalent accuracies as those obtained by static GPS and ground surveying techniques. Numéro de notice : A2016-274 Affiliation des auteurs : non IGN Thématique : POSITIONNEMENT Nature : Article DOI : 10.1179/1752270615Y.0000000021 En ligne : http://doi.org/10.1179/1752270615Y.0000000021 Format de la ressource électronique : URL article Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=80829 [article]

Roof boundary extraction using multiple images / Ahmed F. Elaksher in Photogrammetric record, vol 18 n° 101 (March - May 2003)  

Public [article]  inPhotogrammetric record > vol 18 n° 101 (March - May 2003) . - pp 27 - 40 Titre : Roof boundary extraction using multiple images Type de document : Article/Communication Auteurs : Ahmed F. Elaksher, Auteur ; J.S. Bethel, Auteur ; E. Mikhail, Auteur Année de publication : 2003 Article en page(s) : pp 27 - 40 Note générale : Bibliographie Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Photogrammétrie numérique [Termes IGN] appariement géométrique [Termes IGN] classification dirigée [Termes IGN] cohérence géométrique [Termes IGN] contour [Termes IGN] courbe épipolaire [Termes IGN] détection de contours [Termes IGN] exhaustivité des données [Termes IGN] image aérienne [Termes IGN] méthode robuste [Termes IGN] milieu urbain [Termes IGN] photo-interprétation assistée par ordinateur [Termes IGN] polygone [Termes IGN] reconstruction 3D du bâti [Termes IGN] segmentation d'image Résumé : (Auteur) Urban area building extraction is one of the most challenging problems in photogrammetry. Wellextracted buildings are needed for a variety of applications, such as cartography, building GIS databases for cities, and urban planning. This paper presents a new technique to extract 3D building wireframes using a robust multiimage linematching algorithm. Although one pair of images is adequate to find the 3D position of two visibly corresponding image, features, it is not sufficient to solve the general building extraction problem due to obscured parts in the building. Four images are used in this research to extract the building wireframes. First the images are segmented into regions. Regions are then classified into roof regions and nonroof regions based on their size, shape, and intensity values. The roof region boundary pixels are located and used to find the region perimeters. Region correspondence is solved in a pairwise mode over all images using the epipolar constraint, region size, region shape, and region intensity values. Image lines within the corresponding regions are matched over all images simultaneously by first creating a plane for each region line. Planes are then intersected simultaneously and geometric consistency is used to determine acceptance or rejection. Results with high overlap and sidelap aerial images are presented and evaluated. The results show the completeness and accuracy that this method can provide for extracting complex urban buildings. The average coordinate accuracy is about 08 m using 1:4000 scale aerial photographs scanned at 30 um Six buildings were examined; the line detection rate is 98%. Numéro de notice : A2003-091 Affiliation des auteurs : non IGN Thématique : IMAGERIE Nature : Article DOI : 10.1111/0031-868X.t01-1-00003 En ligne : https://doi.org/10.1111/0031-868X.t01-1-00003 Format de la ressource électronique : URL article Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=22387 [article]

Exemplaires(1)

Code-barres	Cote	Support	Localisation	Section	Disponibilité
106-03011	RAB	Revue	Centre de documentation	En réserve L003	Disponible