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Method for real-time self-calibrating GLONASS code inter-frequency bias and improvements on single point positioning / Liang Chen in GPS solutions, vol 22 n° 4 (October 2018)  

Public [article]  inGPS solutions > vol 22 n° 4 (October 2018) Titre : Method for real-time self-calibrating GLONASS code inter-frequency bias and improvements on single point positioning Type de document : Article/Communication Auteurs : Liang Chen, Auteur ; Min Li, Auteur ; Zhigang Hu, Auteur ; et al., Auteur Année de publication : 2018 Note générale : Bibliographie Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Géodésie spatiale [Termes descripteurs IGN] autoétalonnage [Termes descripteurs IGN] données GLONASS [Termes descripteurs IGN] données GPS [Termes descripteurs IGN] erreur systématique [Termes descripteurs IGN] positionnement ponctuel précis [Termes descripteurs IGN] temps réel Mots-clés libres : code inter-frequency bias (cIFB) Résumé : (Auteur) Utilization of frequency-division multiple access (FDMA) leads to GLONASS pseudorange and carrier phase observations suffering from variable levels inter-frequency bias (IFB). The bias related with carrier phase can be absorbed by ambiguities. However, the unequal code inter-frequency bias (cIFB) will degrade the accuracy of pseudorange observations, which will affect positioning accuracy and convergence of precise point positioning (PPP) when including GLONASS satellites. Based on observations made on un-differenced (UD) ionospheric-free combinations, GLONASS cIFB parameters are estimated as a constant to achieve GLONASS cIFB real-time self-calibration on a single station. A total of 23 stations, with different manufacturing backgrounds, are used to analyze the characteristics of GLONASS cIFB and its relationship with variable receiver hardware. The results show that there is an obvious common trend in cIFBs estimated using broadcast ephemeris for all of the different manufacturers, and there are unequal GLONASS inter-satellite cIFB that match brand manufacture. In addition, a particularly good consistency is found between self-calibrated receiver-dependent GLONASS cIFB and the IFB products of the German Research Centre for Geosciences (GFZ). Via a comparative experiment, it is also found that the algorithm of cIFB real-time self-calibration not only corrects receiver-dependent cIFB, but can moreover eliminate satellite-dependent cIFB, providing more stable results and further improving global navigation satellite system (GNSS) point positioning accuracy. The root mean square (RMS) improvements of single GLONASS standard point positioning (SPP) reach up to 54.18 and 53.80% in horizontal and vertical direction, respectively. The study’s GLONASS cIFB self-estimation can realize good self-consistency between cIFB and stations, working to further promote convergence efficiency relative to GPS + GLONASS PPP. An average improvement percentage of 19.03% is observed, realizing a near-consistent accuracy with GPS + GLONASS fusion PPP. Numéro de notice : A2018-378 Thématique : POSITIONNEMENT Nature : Article nature-HAL : ArtAvecCL-RevueIntern DOI : 10.1007/s10291-018-0774-2 date de publication en ligne : 17/08/2018 En ligne : https://doi.org/10.1007/s10291-018-0774-2 Format de la ressource électronique : URL article Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=90782 [article]

Self-calibration of omnidirectional multi-cameras including synchronization and rolling shutter / Thanh-Tin Nguyen in Computer Vision and image understanding, vol 162 (September 2017)  

Public [article]  inComputer Vision and image understanding > vol 162 (September 2017) . - pp 166 - 184 Titre : Self-calibration of omnidirectional multi-cameras including synchronization and rolling shutter Type de document : Article/Communication Auteurs : Thanh-Tin Nguyen, Auteur ; Maxime Lhuillier, Auteur Année de publication : 2017 Article en page(s) : pp 166 - 184 Note générale : bibliographie Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Acquisition d'image(s) et de donnée(s) [Termes descripteurs IGN] autoétalonnage [Termes descripteurs IGN] compensation par faisceaux [Termes descripteurs IGN] image vidéo [Termes descripteurs IGN] séquence d'images [Termes descripteurs IGN] structure-from-motion [Termes descripteurs IGN] synchronisation Résumé : (auteur) 360° and spherical cameras become popular and are convenient for applications like immersive videos. They are often built by fixing together several fisheye cameras pointing in different directions. However their complete self-calibration is not easy since the consumer fisheyes are rolling shutter cameras which can be unsynchronized. Our approach does not require a calibration pattern. First the multi-camera model is initialized thanks to assumptions that are suitable to an omnidirectional camera without a privileged direction: the cameras have the same setting and are roughly equiangular. Second a frame-accurate synchronization is estimated from the instantaneous angular velocities of each camera provided by monocular structure-from-motion. Third both inter-camera poses and intrinsic parameters are refined using multi-camera structure-from-motion and bundle adjustment. Last we introduce a bundle adjustment that estimates not only the usual parameters but also a sub-frame-accurate synchronization and the rolling shutter. We experiment using videos taken by consumer cameras mounted on a helmet and moving along trajectories of several hundreds of meters or kilometers, and compare our results to ground truth. Numéro de notice : A2017-562 Thématique : IMAGERIE Nature : Article nature-HAL : ArtAvecCL-RevueIntern DOI : 10.1016/j.cviu.2017.08.010 En ligne : https://doi.org/10.1016/j.cviu.2017.08.010 Format de la ressource électronique : URL article Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=86643 [article]

Camera self-calibration with lens distortion from a single image / Dan Liu in Photogrammetric Engineering & Remote Sensing, PERS, vol 82 n° 5 (May 2016)  

Public [article]  inPhotogrammetric Engineering & Remote Sensing, PERS > vol 82 n° 5 (May 2016) . - pp 325 - 334 Titre : Camera self-calibration with lens distortion from a single image Type de document : Article/Communication Auteurs : Dan Liu, Auteur ; Xuejun Liu, Auteur ; Meizhen Wang, Auteur Année de publication : 2016 Article en page(s) : pp 325 - 334 Note générale : Bibliographie Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Acquisition d'image(s) et de donnée(s) [Termes descripteurs IGN] autoétalonnage [Termes descripteurs IGN] contrainte géométrique [Termes descripteurs IGN] étalonnage de capteur (imagerie) [Termes descripteurs IGN] photogrammétrie terrestre Résumé : (Auteur) This paper presents an effective approach for self-calibration with lens distortion using a single image combined with geometric constraints including vanishing points and ellipses. To improve the accuracy of self-calibration, radial distortion and distortion center are included in the calibration procedure. First, assuming image center as the symmetric center, the first radial distortion coefficient and vanishing points are simultaneously optimized from line segments in the image. Second, by utilizing the optimized vanishing points and extracted ellipse, principal distance and principal point are estimated. Last, distortion center is set as the current calculated principal point, and the above steps are then repeated until the principal point reaches a stable solution. Extensive quantitative and qualitative studies of the approach are performed. The experiments pertaining to simulated and real images demonstrate that the approach is effective and suitable and that the approach obtains satisfactory results. Numéro de notice : A2016-409 Thématique : IMAGERIE Nature : Article En ligne : http://dx.doi.org/10.14358/PERS.82.5.325 Format de la ressource électronique : URL article Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=81274 [article]

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Improved area-based deformation analysis of a radio telescope’s main reflector based on terrestrial laser scanning / Christoph Holst in Journal of applied geodesy, vol 9 n° 1 (March 2015)  

Public [article]  inJournal of applied geodesy > vol 9 n° 1 (March 2015) . - pp 1 - 14 Titre : Improved area-based deformation analysis of a radio telescope’s main reflector based on terrestrial laser scanning Type de document : Article/Communication Auteurs : Christoph Holst, Auteur ; Axel Nothnagel, Auteur ; Martin Blome, Auteur ; et al., Auteur Année de publication : 2015 Article en page(s) : pp 1 - 14 Note générale : bibliographie Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Lasergrammétrie [Termes descripteurs IGN] autoétalonnage [Termes descripteurs IGN] déformation d'édifice [Termes descripteurs IGN] données lidar [Termes descripteurs IGN] données localisées 3D [Termes descripteurs IGN] radiotélescope [Termes descripteurs IGN] segmentation [Termes descripteurs IGN] semis de points Résumé : (auteur) The main reflectors of radio telescopes deform due to gravitation when changing their elevation angle. This can be analyzed by scanning the paraboloid surface with a terrestrial laser scanner and by determining focal length variations and local deformations from best-fit approximations. For the Effelsberg radiotelescope, both groups of deformations are estimated from seven points clouds measured at different elevation angles of the telescope: the focal length decreases by 22.7 mm when tilting the telescope from 90 deg to 7.5 deg elevation angle. Variable deformations of ± 2 mm are detected as well at certain areas. Furthermore, a few surface panels seem to be misaligned. Apart from these results, the present study highlights the need for an appropriate measurement concept and for preprocessing stepswhen using laser scanners for area-based deformation analyses. Especially, data reduction, object segmentation and laser scanner calibration are discussed in more detail. An omission of these steps would significantly degrade the deformation analysis and the significance of its results. This holds for all sorts of laser scanner based analyses. Numéro de notice : A2015-026 Thématique : IMAGERIE/POSITIONNEMENT Nature : Article En ligne : http://www.degruyter.com/view/j/jag.2015.9.issue-1/jag-2014-0018/jag-2014-0018.x [...] Format de la ressource électronique : URL article Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=76879 [article]

In-flight photogrammetric camera calibration and validation via complementary lidar / A.S. Gneeniss in ISPRS Journal of photogrammetry and remote sensing, vol 100 (February 2015) 

Public [article]  inISPRS Journal of photogrammetry and remote sensing > vol 100 (February 2015) . - pp 3 - 13 Titre : In-flight photogrammetric camera calibration and validation via complementary lidar Type de document : Article/Communication Auteurs : A.S. Gneeniss, Auteur ; J.P. Mills, Auteur ; P.E. Miller, Auteur Année de publication : 2015 Article en page(s) : pp 3 - 13 Note générale : Bibliographie Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Acquisition d'image(s) et de donnée(s) [Termes descripteurs IGN] ajustement de paramètres [Termes descripteurs IGN] analyse comparative [Termes descripteurs IGN] autoétalonnage [Termes descripteurs IGN] chambre de prise de vue numérique [Termes descripteurs IGN] compensation par faisceaux [Termes descripteurs IGN] données lidar [Termes descripteurs IGN] étalonnage en vol [Termes descripteurs IGN] extraction automatique [Termes descripteurs IGN] instrumentation Applanix [Termes descripteurs IGN] méthode des moindres carrés [Termes descripteurs IGN] point d'appui [Termes descripteurs IGN] UltraCam Résumé : (auteur) This research assumes lidar as a reference dataset against which in-flight camera system calibration and validation can be performed. The methodology utilises a robust least squares surface matching algorithm to align a dense network of photogrammetric points to the lidar reference surface, allowing for the automatic extraction of so-called lidar control points (LCPs). Adjustment of the photogrammetric data is then repeated using the extracted LCPs in a self-calibrating bundle adjustment with additional parameters. This methodology was tested using two different photogrammetric datasets, a Microsoft UltraCamX large format camera and an Applanix DSS322 medium format camera. Systematic sensitivity testing explored the influence of the number and weighting of LCPs. For both camera blocks it was found that when the number of control points increase, the accuracy improves regardless of point weighting. The calibration results were compared with those obtained using ground control points, with good agreement found between the two. Numéro de notice : A2015-050 Thématique : IMAGERIE Nature : Article nature-HAL : ArtAvecCL-RevueIntern Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=75236 [article]

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