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Investigations on the influence of antenna near-field effects and satellite obstruction on the uncertainty of GNSS-based distance measurements / Florian Zimmermann in Journal of applied geodesy, vol 10 n° 1 (March 2016)  

Public [article]  inJournal of applied geodesy > vol 10 n° 1 (March 2016) . - pp 53 - 60 Titre : Investigations on the influence of antenna near-field effects and satellite obstruction on the uncertainty of GNSS-based distance measurements Type de document : Article/Communication Auteurs : Florian Zimmermann, Auteur ; Christian Eling, Auteur ; Heiner Kuhlmann, Auteur Année de publication : 2016 Article en page(s) : pp 53 - 60 Note générale : bibliographie Langues : Anglais (eng) Descripteur : [Termes IGN] antenne GNSS [Termes IGN] distancemètre [Termes IGN] distorsion du signal [Termes IGN] double différence [Termes IGN] étalonnage d'instrument [Termes IGN] trajet multiple [Vedettes matières IGN] Traitement de données GNSS Résumé : (auteur) Antenna near-field effects are one of the accuracy limiting factors on GNSS-based distance measurements. In order to analyse these influences, a measurement campaign at an EDM calibration baseline site with optimum GNSS conditions was performed. To vary the distance between the antenna mount and the absolutely calibrated antennas, spacers with different lengths were used. Due to the comparison of the resulting GNSS-based distance measurements to a reference solution, the influences of the antenna near-field could be analyzed. The standard deviations of the differences to the reference solution, i. e., 0.31 mm for the distance and 0.46 mm for the height component, indicate that equal spacer and antenna combinations at both stations lead to a very high accuracy level. In contrast, different spacer and antenna combinations decrease the accuracy level. Thus, an identical set-up at both antenna stations and the usage of individually calibrated antennas minimize the near-field effects during the double-differencing process. Hence, these aspects can be identified as a prerequisite for highly accurate GNSS-measurements. In addition to near-field effects, the influence of satellite obstructions is investigated. Four realistic shadowing scenarios are numerically simulated on the basis of the observations, which were collected in the optimum surrounding of the EDM calibration baseline site. The comparison to nominal values indicates that a shadowing leads only to a slight decreasing of the accuracy. Consequently, there is a strong suspicion that multipath effects and signal distortions seem to have a greater influence on the accuracy of GNSS-based distance measurements than the satellite constellation. Numéro de notice : A2016-554 Affiliation des auteurs : non IGN Thématique : POSITIONNEMENT Nature : Article DOI : 10.1515/jag-2015-0026 En ligne : http://dx.doi.org/10.1515/jag-2015-0026 Format de la ressource électronique : URL article Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=81704 [article]

Entwicklung einer direkten Georeferenzierungseinheit zur Positions- und Orientierungbestimmung leichter UAVs in Eichzeit / Christian Eling (2016)  

Public Titre : Entwicklung einer direkten Georeferenzierungseinheit zur Positions- und Orientierungbestimmung leichter UAVs in Eichzeit Type de document : Thèse/HDR Auteurs : Christian Eling, Auteur Editeur : Munich : Bayerische Akademie der Wissenschaften Année de publication : 2016 Collection : DGK - C, ISSN 0065-5325 num. 788 Importance : 107 p. Format : 21 x 30 cm ISBN/ISSN/EAN : 978-3-7696-5200-0 Note générale : bibliographie Langues : Allemand (ger) Descripteur : [Vedettes matières IGN] Photogrammétrie numérique [Termes IGN] drone [Termes IGN] géoréférencement direct [Termes IGN] GPS-INS [Termes IGN] magnétomètre [Termes IGN] onde porteuse [Termes IGN] photogrammétrie aérienne [Termes IGN] semis de points [Termes IGN] système de numérisation mobile Résumé : (auteur) In recent years, Unmanned Aerial Vehicles (UAVs) have been used increasingly as mobile mapping platforms for kinematic applications in the field of geodesy. For this purpose a UAV is usually equipped with a mapping sensor, such as a camera or a laserscanner. A major step to make the collected data useful for surveying applications is the georeferencing, which associates the images or range measurements and the derived products (point clouds, orthofotos, 3D models) with a spatial reference. In this dissertation the development of a direct georeferencing system for real-time position and attitude determination of lightweight UAVs is presented. The term „direct" means that the georeferencing is based on an onboard multi-sensor system. Sensors, which are typically used in this context, are GPS (Global Positioning System) receivers, inertial sensors and magnetometers. For geodetic UAV-applications Micro-UAVs are usually applied, which have a weight limit of 5 kg. Therefore, weight, size and power supply constraints play an important role here. As a result of these limitations inertial sensors based on MEMS (Micro Electro Mechanical System) technology are mostly used. This technology enables the compliance with size and weight limits, but it also leads to significant drift effects in the position and attitude determination after a short period of time. To bound these drift effects and to be able to provide high accuracies (e.g. position: 5 cm, attitude: 0.5 deg) in the direct georeferencing of a Micro-UAV, a high availability of precise GPS carrier phase measurements is crucially important. As a consequence the following aspects will be addressed in this dissertation: • GPS carrier phase measurements are ambiguous by an unknown number of integer cycles. These so called ambiguities have to be resolved after every loss of lock of the satellite signals to fully exploit the high accuracies of the carrier phase observables. Since the satellite signals are interrupted frequently during kinematic applications, procedures are developed, implemented and evaluated, which enable a fast ambiguity resolution and allow for a high availability of CPS carrier phase measurements under challenging GPS measurement conditions. • With the aim to realize high accuracies and a high robustness, redundant information from several sensors is integrated in a sensible manner in sensorfusion algorithms In order to be able to deal with challenging GPS measurement conditions, the sensorfusion is realized at the level of GPS raw measurements in a tightly-coupled GPS/MEMS-IMU integration algorithm. In this way GPS carrier phase measurements can even be used, if less than four satellites are visible, which also increases the availability of a precise position estimation. The accuracy improvements of a tightly-coupled over a loosely-coupled integration during challenging GPS measurement conditions are investigated. • The algorithms are implemented on a multi-sensor system, which has been developed for the direct georeferencing of lightweight UAVs in this dissertation. Results of flight tests and measurements with a portable test system demonstrate that the developed direct georeferencing system leads to position accuracies of less than 5 cm and attitude (roll, pitch, yaw) accuracies of less than 0.2 deg, if GPS carrier-phase measurements are available. Overall, this dissertation gives detailed insights into the development of algorithms and a multi-sensor system for the direct georeferencing of lightweight UAVs in real-time. The findings gained in this thesis are not only valid for the position and attitude determination of lightweight UAVs but also for other mobile platforms, such as cars, ships, airplanes or rail-borne vehicles. Therefore, this work makes an important contribution to a current trend in the field of engineering geodesy, where mapping, monitoring and also setting-out is more and more realized using mobile mapping systems. Numéro de notice : 17380 Affiliation des auteurs : non IGN Thématique : IMAGERIE Nature : Thèse étrangère Note de thèse : Dissertation : : Rheinische Friedrich-Wilhelms-Universität Bonn : 2016 DOI : sans En ligne : https://dgk.badw.de/fileadmin/user_upload/Files/DGK/docs/c-788.pdf Format de la ressource électronique : URL Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=84793

Development, calibration and evaluation of a portable and direct georeferenced laser scanning system for kinematic 3D mapping / Erik Heinz in Journal of applied geodesy, vol 9 n° 4 (December 2015)  

Public [article]  inJournal of applied geodesy > vol 9 n° 4 (December 2015) . - pp 227 - 243 Titre : Development, calibration and evaluation of a portable and direct georeferenced laser scanning system for kinematic 3D mapping Type de document : Article/Communication Auteurs : Erik Heinz, Auteur ; Christian Eling, Auteur ; Markus Wieland, Auteur ; Lasse Klingbeil, Auteur ; Heiner Kuhlmann, Auteur Année de publication : 2015 Article en page(s) : pp 227 - 243 Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Lasergrammétrie [Termes IGN] étalonnage d'instrument [Termes IGN] géoréférencement direct [Termes IGN] semis de points [Termes IGN] système de numérisation mobile [Termes IGN] télémètre laser [Termes IGN] variance Résumé : (auteur) In recent years, kinematic laser scanning has become increasingly popular because it offers many benefits compared to static laser scanning. The advantages include both saving of time in the georeferencing and a more favorable scanning geometry. Often mobile laser scanning systems are installed on wheeled platforms, which may not reach all parts of the object. Hence, there is an interest in the development of portable systems, which remain operational even in inaccessible areas. The development of such a portable laser scanning system is presented in this paper. It consists of a lightweight direct georeferencing unit for the position and attitude determination and a small low-cost 2D laser scanner. This setup provides advantages over existing portable systems that employ heavy and expensive 3D laser scanners in a profiling mode. A special emphasis is placed on the system calibration, i. e. the determination of the transformation between the coordinate frames of the direct georeferencing unit and the 2D laser scanner. To this end, a calibration field is used, which consists of differently orientated georeferenced planar surfaces, leading to estimates for the lever arms and boresight angles with an accuracy of mm and one-tenth of a degree. Finally, point clouds of the mobile laser scanning system are compared with georeferenced point clouds of a high-precision 3D laser scanner. Accordingly, the accuracy of the system is in the order of cm to dm. This is in good agreement with the expected accuracy, which has been derived from the error propagation of previously estimated variance components. Numéro de notice : A2015--011 Affiliation des auteurs : non IGN Thématique : IMAGERIE Nature : Article DOI : 10.1515/jag-2015-0011 En ligne : http://dx.doi.org/ 10.1515/jag-2015-0011 Format de la ressource électronique : URL article Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=80763 [article]

UAV real-time: Data use in a lightweight direct georeferencing system / Christian Eling in GPS world, vol 26 n° 11 (November 2015)  

Public [article]  inGPS world > vol 26 n° 11 (November 2015) . - pp 44 - 55 Titre : UAV real-time: Data use in a lightweight direct georeferencing system Type de document : Article/Communication Auteurs : Christian Eling, Auteur ; Lasse Klingbeil, Auteur ; Markus Wieland, Auteur ; Erik Heinz, Auteur ; Heiner Kuhlmann, Auteur Année de publication : 2015 Article en page(s) : pp 44 - 55 Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Acquisition d'image(s) et de donnée(s) [Termes IGN] drone [Termes IGN] géoréférencement direct [Termes IGN] GPS en mode cinématique [Termes IGN] GPS-INS [Termes IGN] magnétomètre [Termes IGN] positionnement cinématique en temps réel [Termes IGN] trajectographie par GPS Résumé : (auteur) Direct georeferencing with onboard sensors is less time-consuming for data processing than indirect georeferencing using ground control points, and can supply real-time navigation capability to a UAV. This is very useful for surveying, precision farming or infrastructure inspection. An onboard system for position and attitude determination of lightweight UAVs weighs 240 grams and produces position accuracies better than 5 centimeters and attitude accuracies better than 1 degree. Numéro de notice : A2015--087 Affiliation des auteurs : non IGN Thématique : IMAGERIE Nature : Article DOI : sans En ligne : http://gpsworld.com/uav-real-time-data-use-in-a-lightweight-direct-georeferencin [...] Format de la ressource électronique : URL article Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=84804 [article]