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Assessing the performance of multi-GNSS precise point positioning in Asia-Pacific region / X. Zhao in Survey review, vol 49 n° 354 (September 2017)  

Public [article]  inSurvey review > vol 49 n° 354 (September 2017) . - pp 186 - 196 Titre : Assessing the performance of multi-GNSS precise point positioning in Asia-Pacific region Type de document : Article/Communication Auteurs : X. Zhao, Auteur ; S. Wang, Auteur ; C. Liu, Auteur ; J. Ou, Auteur ; X. Yu, Auteur Année de publication : 2017 Article en page(s) : pp 186 - 196 Note générale : Bibliographie Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Géodésie spatiale [Termes IGN] Asie (géographie politique) [Termes IGN] données BeiDou [Termes IGN] données GLONASS [Termes IGN] données GPS [Termes IGN] filtre de Kalman [Termes IGN] modèle stochastique [Termes IGN] Pacifique (océan) [Termes IGN] positionnement ponctuel précis [Termes IGN] test de performance Résumé : (Auteur) Multi-Global Navigation Satellite System (GNSS) integration can effectively improve the satellite geometry strength, and certain effect on the precise point positioning (PPP) accuracy and convergence speed. Taking the system difference into account, this paper deduces the unified GNSS observation model, which is extended to the multi-GNSS PPP functional model. Meanwhile, the stochastic model used in Kalman filter parameter estimation is presented in the paper. Furthermore, to evaluate the performance of the multi-GNSS PPP in Asia-Pacific region, observed data from the International GNSS Service reference stations are analysed using the self-developed software. In detail, the results from Global Positioning System (GPS)-, GLObal NAvigation Satellite System (GLONASS)- and BeiDou Navigation Satellite System (BDS)-only PPP, double combined PPP and GPS/GLONASS/BDS combined PPP under the different observation duration and cut-off elevation angles are analysed. Results demonstrate: (1) compared with the single system PPP, the convergence speed of the multi-GNSS PPP is improved while the accuracy is not significantly improved after processing the 24-h data set; (2) when the observation duration is short, such as 0.5 h, the mean convergence percentage of the BDS combined with GPS and GLONASS PPP increases by an average of 49.6% compared with the single individual systems except for BDS, respectively, under the cut-off angle of 5° and (3) when PPP positioning with high cut-off elevation angles, and at the point of centimetre-level positioning, the GPS/GLONASS/BDS combined PPP has a better performance on the convergence percentage and convergence speed. For example, the percentages of the position biases within 0–5 cm for GPS/GLONASS/BDS are increased by 7.2 and 4.5% in North and East direction compared with GPS/GLONASS under the cut-off angle of 35°, more than any other. And the mean convergence time is only 14.5 min. Numéro de notice : A2017-544 Affiliation des auteurs : non IGN Thématique : POSITIONNEMENT Nature : Article DOI : 10.1080/00396265.2016.1151576 En ligne : https://doi.org/10.1080/00396265.2016.1151576 Format de la ressource électronique : URL article Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=86599 [article]

A low-cost multi-sensoral mobile mapping system and its feasibility for tree measurements / Anttoni Jaakkola in ISPRS Journal of photogrammetry and remote sensing, vol 65 n° 6 (November - December 2010)  

Public [article]  inISPRS Journal of photogrammetry and remote sensing > vol 65 n° 6 (November - December 2010) . - pp 514 - 522 Titre : A low-cost multi-sensoral mobile mapping system and its feasibility for tree measurements Type de document : Article/Communication Auteurs : Anttoni Jaakkola, Auteur ; Antero Kukko, Auteur ; X. Yu, Auteur ; Juha Hyyppä, Auteur ; et al., Auteur Année de publication : 2010 Article en page(s) : pp 514 - 522 Note générale : Bibliographie Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Acquisition d'image(s) et de donnée(s) [Termes IGN] arbre (flore) [Termes IGN] capteur aérien [Termes IGN] chambre DTC [Termes IGN] données lidar [Termes IGN] données localisées 3D [Termes IGN] drone [Termes IGN] géoréférencement direct [Termes IGN] GPS-INS [Termes IGN] lasergrammétrie [Termes IGN] lidar topographique [Termes IGN] rayonnement infrarouge thermique [Termes IGN] semis de points [Termes IGN] spectromètre [Termes IGN] système de numérisation mobile [Termes IGN] télémètre laser aéroporté [Termes IGN] télémétrie laser aéroporté Résumé : (Auteur) This paper presents a novel low-cost mini-UAV-based laser scanning system, which is also capable of performing car-based mobile mapping. The quality of the system and its feasibility for tree measurements was tested using the system’s laser scanner. The system was constructed as a modular measurement system consisting of a number of measurement instruments: a GPS/IMU positioning system, two laser scanners, a CCD camera, a spectrometer and a thermal camera. An Ibeo Lux and a Sick LMS151 profile laser were integrated into the system to provide dense point clouds; intensities of the reflected echoes can also be obtained with the Sick LMS. In our tests, when using a car as a platform, the pole-type object extraction algorithm which was developed resulted in 90% completeness and 86% correctness. The heights of pole-type objects were obtained with a bias of -1.6 cm and standard deviation of 5.4 cm. Using a mini-UAV as the platform, the standard deviation of individual tree heights was about 30 cm. Also, a digital elevation model extraction was tested with the UAV data, resulting in a height offset of about 3.1 cm and a standard deviation of 9.2 cm. With a multitemporal point cloud, we demonstrated a method to derive the biomass change of a coniferous tree with an R2 value of 0.92. The proposed system is capable of not only recording point cloud data giving the geometry of the objects, but also simultaneously collecting image data, including overlapping images and the intensity of laser backscatter, as well as hyperspectral and thermal data. Therefore we believe that the system is feasible for new algorithm and concept development and for basic research, especially when data is recorded multitemporally. Numéro de notice : A2010-484 Affiliation des auteurs : non IGN Thématique : FORET/IMAGERIE Nature : Article nature-HAL : ArtAvecCL-RevueIntern DOI : 10.1016/j.isprsjprs.2010.08.002 En ligne : https://doi.org/10.1016/j.isprsjprs.2010.08.002 Format de la ressource électronique : URL article Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=30677 [article]

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081-2010061	SL	Revue	Centre de documentation	Revues en salle	Disponible

Change detection techniques for canopy height growth measurements using airborne laser scanner data / X. Yu in Photogrammetric Engineering & Remote Sensing, PERS, vol 72 n° 12 (December 2006)  

Public [article]  inPhotogrammetric Engineering & Remote Sensing, PERS > vol 72 n° 12 (December 2006) . - pp 1339 - 1348 Titre : Change detection techniques for canopy height growth measurements using airborne laser scanner data Type de document : Article/Communication Auteurs : X. Yu, Auteur ; Juha Hyyppä, Auteur ; et al., Auteur Année de publication : 2006 Article en page(s) : pp 1339 - 1348 Note générale : Bibliographie Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Lasergrammétrie [Termes IGN] analyse diachronique [Termes IGN] détection de changement [Termes IGN] données lidar [Termes IGN] données localisées 3D [Termes IGN] forêt boréale [Termes IGN] hauteur des arbres [Termes IGN] houppier [Termes IGN] instrumentation Toposys [Termes IGN] modèle numérique de surface [Termes IGN] objet géographique ponctuel [Termes IGN] Pinus sylvestris [Termes IGN] semis de points Résumé : (Auteur) This paper analyzes the potential of airborne laser scanner data for measuring individual tree height growth in a boreal forest using 82 sample trees of Scots pine. Point clouds (10 points/m2, beam size 40 cm) illuminating 50 percent of the treetops were acquired in September 1998 and May 2003 with the Toposys 83 kHz lidar system. The reference height and height growth of pines were measured with a tacheometer in the field. Three different types of features were extracted from the point clouds representing each tree; they were the difference between the highest z values, the difference between the DSMs of the tree crown, and the differences between the 85th, 90th and 95th percentiles of the canopy height histograms corresponding to the crown. The best correspondence with the field measurements was achieved with an R2 value of 0.68 and a RMSE of 43 cm. The results indicate that it is possible to measure the growth of an individual tree with multi-temporal laser surveys. We also demonstrated a new algorithm for tree-to-tree matching. It is needed in operational growth estimation based on individual trees, especially in dense spruce forests. The method is based on minimizing the distances between treetops in the N- dimensional data space. The experiments showed that the use of the location (derived from laser data) and height of the trees were together adequate to provide reliable tree-to-tree matching. In the future, a fourth dimension (the crown area) should also be included in the matching. Copyright ASPRS Numéro de notice : A2006-543 Affiliation des auteurs : non IGN Thématique : FORET/IMAGERIE Nature : Article DOI : 10.14358/PERS.72.12.1339 En ligne : https://doi.org/10.14358/PERS.72.12.1339 Format de la ressource électronique : URL article Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=28266 [article]

Orientation of optical airborne and spaceborne images for small and medium scale mapping purposes / Eija Honkavaara (1999)

Public Titre : Orientation of optical airborne and spaceborne images for small and medium scale mapping purposes Type de document : Rapport Auteurs : Eija Honkavaara, Auteur ; Mirjam Bilker, Auteur ; X. Yu, Auteur ; Juha Jaakkola, Auteur ; Harri Kaartinen, Auteur ; J. Ylonen, Auteur Editeur : Helsinki : Finnish Geodetic Institute FGI Année de publication : 1999 Collection : Reports of the Finnish Geodetic Institute num. 99-5 Importance : 57 p. Format : 21 x 30 cm Note générale : Bibliographie Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Photogrammétrie numérique [Termes IGN] aérotriangulation [Termes IGN] image aérienne [Termes IGN] image JERS [Termes IGN] image optique [Termes IGN] image spatiale [Termes IGN] orientation d'image [Termes IGN] orientation du capteur [Termes IGN] photographie à moyenne échelle [Termes IGN] photographie à petite échelle [Termes IGN] point d'appui [Termes IGN] point de vérification [Termes IGN] points homologues Index. décimale : 33.30 Photogrammétrie numérique Résumé : (Auteur) Recent technical progress has resulted in significant improvement of the orientation process. The most revolutionary developments include automation of tie point measurement and direct determination of orientation parameters with GPS and INS techniques. Options to be taken into account when selecting materials for mapping and methods for orientation include image type (scale; standard frame, digital camera; spaceborne, airborne), block geometry (single image orientation, aerial triangulation (AT)), ground control (targeted, untargeted, GIS data, etc.), image observations (automatic, interactive) and utilisation of directly measured orientation parameters. The task is to optimise costs, accuracy and reliability. These questions have been investigated at the Finnish Geodetic Institute (FGI) for medium and small scale mapping applications with spatial resolution and accuracy requirements for 15 m. Both theoretical and empirical considerations have been made with respect to several variables: observations of orientation parameters (GPS, no GPS, GPS processing), block structure (cross strips, no cross strips; single image, block), ground control points (GCPs, targeted, untargeted and GIS data: nationwide digital orthophotos, base maps and elevation models), image observations of tie points and GCPs (interactive, automatic) and image material (1:31 000 and 1:60 000 standard airborne images with approximately 1 m and 5 m pixel sizes; JERS/VNIR satellite images). All the airborne cases were analysed using the same strategies and checkpoints. JERSIVNIR images were analysed in parallel with the airborne images, but no comprehensive comparisons between the materials could be made because of large resolution differences. The results of GPS measurements of perspective centres showed offsets and linear drifts varying from strip to strip, but compensation in AT with minimum ground control was possible. Targeted GCPs yielded high accuracy and reliability. Untargeted GCPs and GIS data as ground control, especially digital orthophotos and DEM25, also yielded good accuracy, although care is needed to avoid problems with gross errors. With GIS data, systematic errors can also be expected. The empirical and simulation results obtained make it possible to select GCP materials for obtaining various accuracy levels in the cases of spatial resection and AT with or without GPS support. It was concluded that in block adjustment, a planimetric accuracy of 10 gm in the image and a height accuracy of 0.1%oH can be obtained by using a reasonable number of GCPs (e.g. in 4 base distances) with accuracy better than 20 µm in image. Several examples of suitable GCP materials and configurations for obtaining accuracy better than 1 m were given. High accuracy was obtained with automatic tie point measurement, but investigations are still needed concerning optimal adjustment methods and number of points. The results, however, were in any case sufficient for applications with medium quality requirements. Experiences of orientation of JERS/VNIR images with rigorous methods were good; accuracy of 0.4 pixels was obtained with only 4 GCPs. In all the cases, the results of empirical and theoretical investigations correlated as long as the assumptions were valid; therefore reliable knowledge of the quality of the materials used as the basis for orientation is an important presupposition. Numéro de notice : 67564 Affiliation des auteurs : non IGN Thématique : IMAGERIE Nature : Rapport Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=44680

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