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Titre : Troposphere modeling and filtering for precise GPS leveling Type de document : Thèse/HDR Auteurs : Frank Kleijer, Auteur Editeur : Delft : Netherlands Geodetic Commission NGC Année de publication : 2004 Collection : Netherlands Geodetic Commission Publications on Geodesy, ISSN 0165-1706 num. 56 Importance : 262 p. Format : 17 x 24 cm ISBN/ISSN/EAN : 978-90-6132-284-9 Note générale : Bibliographie Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Rayonnement électromagnétique
[Termes IGN] correction troposphérique
[Termes IGN] filtre de Kalman
[Termes IGN] modèle stochastique
[Termes IGN] nivellement par GPS
[Termes IGN] positionnement par GNSS
[Termes IGN] propagation troposphérique
[Termes IGN] simulation
[Termes IGN] traitement de données GNSS
[Termes IGN] troposphèreIndex. décimale : 24.30 Rayonnement électromagnétique Résumé : (Auteur) Precision : In the Netherlands, a precision of 5 rnm for estimated GPS height differ ences is required to achieve comparable accuracy as geoid height differences. This precision can be achieved for 24-hour data sets when applying a proper modeling. Precise levelling with GPS requires a judicious modeling of tropospheric delays, which has physical, functional, and stochastic aspect.
Modeling aspects : The physical modeling comprises zenith delays for the hydrostatic and wet component and zenith angle dependent mapping functions. Because the amount of water vapor in the atmosphere fluctuates widely and because the water-vapor aspect induced signal delays affect the height component strongly, a-priori modeling of these delays results in an insufficient precision of height differences. Parameterizing the tropospheric delay in the functional model is therefore necessary, at least for medium and long baselines. The observation model can further be strengthened by pseudo-observations. These pseudo-observations may be spatiotemporal constraints on tropospheric delay differences, or constraints on residual slant delays. With the latter type of constraint the isotropy assumption is loosened. An existing theoretical model is revised to obtain the corresponding covariance matrix. The stochastic modeling of both types of constraints is based on the assumption of Kohnogorov turbulence.
Filtering : The observation models can be implemented in a recursive filter like the Kalman Filter or the SRIF Several variations of these filters are described. For fast computations the most suitable recursive filtering technique is the Kalman-Cholesky Filter with pre-elimination of temporal GPS parameters, such as clock errors and ionospheric delays. Some tests and reliability descriptions are worked out for this filter. For practical implementation the temporal behavior of the zenith wet delay is to be assumed a random-walk process, which gives a fair description. The zenith wet delay can be estimated every epoch or every pre-defined batch of epochs.
Impact of model components : The effect of several model components on mainly the height is analyzed by simulation software. Special attention is given to the residual-slant-delay model because it is potentially precision and reliability improving. The impact of this model does however depend on the precision level of the observations and it still needs to be validated. Although observations to low-elevation satellites have a large contribution to the precision of the height, the residual-slant-delay model implies a strong down weighting of observations to satellites below ten degrees elevation. The highest accuracy can be obtained when the phase ambiguities are fixed. Even for long observation time spans this makes a difference of up effect on the formal precision of the height, but they have, a large influence on the precision of the filtered zenith delays. Because overconstraining (with constraints that are too tight) can have a large precision-deteriorating effect, spat iotemporal constraints are not recommended for GPS leveling. Further, short batches are preferred to avoid biases. To prevent the presence of near rank deficiencies, the zenith delays of one station are often fixed. From a precision point of view this is not necessary and is not recommended because this can also introduce biases. Even larger biases can be introduced when the zenith delays of all stations are fixed to their a-priori values. For very short baselines (< ±1 kin), this model is however justifiable because the formal precision improves considerately, keeping the effect of the biases in balance. to 15-20%. Batch size and spatiotemporal constraints turned out to have little effect on the formal precision of the height, but they have, a large influence on the precision of the filtered zenith delays. Because overconstraining (with constraints that are too tight) can have a large precision-deteriorating effect, spat iotemporal constraints are not recommended for GPS leveling. Further, short batches are preferred to avoid biases. To prevent the presence of near rank deficiencies, the zenith delays of one station are often fixed. From a precision point of view this is not necessary and is not recommended because this can also introduce biases. Even larger biases can be introduced when the zenith delays of all stations are fixed to their a-priori values. For very short baselines (< ±1 kin), this model is however justifiable because the formal precision improves considerately, keeping the effect of the biases in balance.Note de contenu : General introduction
I) Troposphere delay modeling for space geodetic measurements
Symbols and units in Part I
3 Introduction to Part I
4 Physics of the atmosphere
5 Zenith-delay models
6 Slant-delay models
7 Azimuthal asymmetry and gradient parameters
8 Conclusions of Part 1
A Temperature lapse rate
B Saastamoinen integrals
C Effective height
Bibliography
II) Paramerization of the tropospheric delay in GPS observation models
Symbols of Part II
9 Introduction to Part II
10 GPS observation equations
11 Eliminating rank deficiencies in troposphere-fixed models
12 Troposphere-float and weighted models
13 Near rank deficiencies
14 Pre-elimination transformations
15 Conclusions of Part II
III) Stochastic modeling of (slant) tropospheric delays observed by GPS
Symbols of Part III
16 Introduction to Part III
17 Power-law processes
18 Stochastic modeling of troposphere constraints
19 Conclusions of Part III
IV) Recursive GPS data processing
Symbols of Part IV
20 Introduction to Part IV
21 Kalman filtering with pre-elimination
22 Pre-elimination in a recursive SRIF
23 Implementation aspects
24 Condition equations, testing, and reliability
25 Conclusions of Part IV
V) Simulations
Symbols of Part V
26 Introduction to Part V
27 Software implementation
28 Means of quality assessment
29 Simulation scenarios
30 The troposphere-fixed model
31 Conclusions of Part V
32 Conclusions and recommendationsNuméro de notice : 16056 Affiliation des auteurs : non IGN Thématique : IMAGERIE Nature : Thèse étrangère En ligne : https://ncgeo.nl/downloads/56Kleijer.pdf Format de la ressource électronique : URL Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=55149 Réservation
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Troposphere modeling and filteringAdobe Acrobat PDF Automated aggregation of geographic objects / J.W.N. van Smaalen (2003)
Titre : Automated aggregation of geographic objects : a new approach to the conceptual generalisation of geographic databases Type de document : Thèse/HDR Auteurs : J.W.N. van Smaalen, Auteur Editeur : Delft : Netherlands Geodetic Commission NGC Année de publication : 2003 Collection : Netherlands Geodetic Commission Publications on Geodesy, ISSN 0165-1706 num. 55 Importance : 94 p. Format : 17 x 24 cm ISBN/ISSN/EAN : 978-90-6132-282-5 Note générale : Bibliographie
doctoral dissertationLangues : Anglais (eng) Descripteur : [Termes IGN] agrégation de données
[Termes IGN] base de données localisées
[Termes IGN] généralisation cartographique automatisée
[Termes IGN] généralisation de base de données
[Termes IGN] implémentation (informatique)
[Termes IGN] modèle (conceptuel) de généralisation
[Termes IGN] modèle conceptuel de données
[Termes IGN] modèle topologique de données
[Termes IGN] relation spatiale
[Termes IGN] représentation multiple
[Vedettes matières IGN] GénéralisationRésumé : (Auteur) Since the late 1960's automated methods for map generalisation have been studied, but thus far no comprehensive system has been achieved. This is due to the general complexity of the matter, part of which is caused by the inability to separate the conceptual and the graphic issues. These aspects of map generalisation are considered separate issues ever since the advent of GIS but in practice it has been difficult to disconnect the conceptual issues from the impediments of graphic representation, either in the form of a paper map or on a computer screen. Current research into automated map generalisation generally appears to be in a cul-de-sac for this reason.
This study therefore aims to concentrate on strictly non-graphic operations and large generalisation steps, i.e. big scale changes. Whereas most existing methods work towards a clear end result, this approach does not. Instead, it is entirely based on the input data. Minimizing generalisation errors is a priority and assessment of the generalisation results is also an issue to consider. The goal is to develop a system for the generalisation of object-and vector-based categorical maps, such as large-scale topographic data, that is to a large extent automated and can be operated by non-expert users. In the past, several generalisation procedures have been developed for individual objects and dichotomous maps, but the number of procedures for categorical maps is still limited and the methods that do exist rely on similarity and importance factors that are hard to determine.
Large-scale categorical data mostly form an area partition, i.e. the whole spatial extent of the dataset is covered by objects and the objects do not overlap. This implies that objects cannot simply be removed - since this would cause 'holes' -but have to be combined or aggregated.
Objects can be aggregated based on taxonomy or partonomy relationships. Taxonomy relationships are based on similarity between the objects or classes. Aggregation based on taxonomy relationships has been described extensively in map generalisation literature, but only works within a limited spatial range. Since this study is aimed at large-scale changes it is based on the much less described partonomy relationships. Inter-object and inter-class relationships are used to determine functionally related classes in order to aggregate the object instances of the class. It is assumed that spatial correlations indicate functional relationships. The class adjacency index is used as a measure of spatial correlation between classes. Combinations of classes with a high class adjacency index are likely candidates for the creation of composite classes. Adjacent objects of these classes can subsequently be aggregated and reclassified to create composite objects.
The class adjacency index is determined based on adjacency measures of the member objects. The input dataset must therefore form a topologically correct, object-based area partition. The implementation is based on a stored adjacency graph and uses regular relational database management software. The data model is object-based and supports the concept of composite objects. In the process a multiple representations dataset is produced by connecting the composite objects created in every aggregation cycle to the constituent parts in the previous level.
The process can be fully automated but it is also possible to allow user interaction at several points in the process without compromising the approach. Since it is entirely based on characteristics of the input dataset, the method is also suited for exploratory purposes. To a certain degree, the meaning of the classes is not even relevant, although in interactive mode the user naturally has to be aware of the classes.
The method was applied to two Dutch topographic datasets: TOP10 vector and GBKN. The results show that this is a very promising method for conceptual generalisation. The concept of composite classes makes that generalisation errors are not an issue. Therefore, it cannot be evaluated using conventional generalisation effect measures. The output of the aggregation process is not readily suitable for mapping purposes, and additional cartographic generalisation is in that case required. The current implementation is not intended as a complete solution for conceptual generalisation. But since it is set in an environment of other conceptual generalisation operations, such as structural generalisation and extended adjacency graphs, it can be extended to create such a comprehensive system.Note de contenu : Chapter 1 : Introduction
Chapter 2 : Related literature
Chapter 3 : Conceptual data model
Chapter 4 : Abstraction process
Chapter 5 : Datasets
Chapter 6 : Implementation
Chapter 7 : Results and discussion
Chapter 8 : Conclusions and recommendationsNuméro de notice : 15084 Affiliation des auteurs : non IGN Thématique : GEOMATIQUE/INFORMATIQUE Nature : Thèse étrangère Note de thèse : PhD thesis : Geo-information : Wageningen University : 2003 Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=55057 Réservation
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Code-barres Cote Support Localisation Section Disponibilité 15084-02 37.10 Livre Centre de documentation Géomatique Disponible 15084-01 37.10 Livre Centre de documentation Géomatique Disponible 15084-03 37.10 Livre Centre de documentation Géomatique Disponible
Titre : Automation in architectural photogrammetry : Line photogrammetry for the reconstruction from single and multiple images Type de document : Thèse/HDR Auteurs : Frank van den Heuvel, Auteur ; M. George Vosselman, Auteur Editeur : Delft : Netherlands Geodetic Commission NGC Année de publication : 2003 Collection : Netherlands Geodetic Commission Publications on Geodesy, ISSN 0165-1706 num. 54 Importance : 190 p. Format : 17 x 24 cm ISBN/ISSN/EAN : 978-90-6132-281-8 Note générale : Bibliographie Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Photogrammétrie terrestre
[Termes IGN] automatisation
[Termes IGN] caméra numérique
[Termes IGN] détection de contours
[Termes IGN] méthode des moindres carrés
[Termes IGN] métrologie
[Termes IGN] patrimoine culturel
[Termes IGN] photogrammétrie architecturale
[Termes IGN] photogrammétrie métrologique
[Termes IGN] photogrammétrie terrestre
[Termes IGN] reconstruction 3D du bâti
[Termes IGN] traitement d'image
[Termes IGN] vision par ordinateurIndex. décimale : 33.70 Photogrammétrie terrestre Résumé : (Auteur) Architectural photogrammetry has been practised for more than a century with the documentation of cultural heritage as its main objective. Since the introduction of the computer, and later the digital camera, research in photogrammetry aims at automation. This thesis reports on research on automation in architectural photogrammetry for efficient reconstruction of detailed building models from one or more possibly widely separated digital closerange images. This research is on the fringes of photogrammetry and computer vision. It treats topics frequently studied in computer vision in a photogrammetric way and offers new solutions. This approach is characterised by:
- Robust and direct solutions for approximate value computation Statistical testing of consistency of redundant information
- Integral leastsquares adjustment of all information for optimal parameter estimation Quality control by statistical testing and error propagation
- Semiautomatic processing, aiming at a reliable solution with a minimum of user interaction
- Precalibration of the camera's used
- Exploitation of generic knowledge of the object shape Use of image lines as the basic type of observations.
The research is presented in the form of a collection of papers published between 1997 and 2002. Furthermore, the methods described in the papers have also been applied to a reference set of images. The results of these experiments are presented in a separate chapter.
The demand for models of the built environment has increased due to the development of computer applications such as virtual and augmented reality, and computer games. In these applications the required accuracy of the models is not as high as in traditional applications of architectural photogrammetry, such as documentation of cultural heritage. Emphasis in research has shifted towards efficient production of computer models that show a high level of realism. [...]
The processing of images of the CIPA reference data set has demonstrated the capabilities and limitations of the developed methods for camera calibration, image orientation, and object reconstruction. Calibration of the camera was performed semiautomatically with five images of the reference data set. The results were compared with the camera information available from the reference data set. The maximum parameter difference was three times its standard deviation.
The two different methods for image orientation have been applied on four images taken at the corners of the building. The first one is based on the reconstruction of rectangles from a single image. Resulting orientations differ less than 4 degrees from the adjusted values derived in a bundle adjustment. With the second more automated method a correct approximate solution was obtained for all image pairs using two or three manually measured corresponding points. Full automation of relative orientation was not possible for all image pairs due to the repeating structures in the fagades and for imagery where image scale differences were large.
An object model was reconstructed based on a linephotogrammetric bundle adjustment of manual fine measurements in the same four images. Geometric object constraints made the reconstruction of occluded object points possible, improved regularity of the building model and strengthened the geometry of the network.
The research presented in this thesis contributes to the fields of photogrammetry and computer vision. However, emphasis is on photogrammetry where manual or semiautomatic measurement methods prevail and leastsquares adjustment is the tool commonly applied for parameter estimation. The developed linephotogrammetric bundle adjustment model that allows the incorporation of object shape knowledge is the main contribution to this field. Computer vision is generally more focussed on automation, single image processing, and the use of uncalibrated cameras. Therefore, the methods developed for vanishing point detection, used for image orientation and camera calibration, and the methods developed for reconstruction from a single image are primarily in the field of computer vision. In conclusion, this thesis contributes to bringing photogrammetry and computer vision closer together, which will be beneficial to both fields.Numéro de notice : 15053 Affiliation des auteurs : non IGN Thématique : IMAGERIE Nature : Thèse étrangère En ligne : https://www.ncgeo.nl/downloads/54VandenHeuvel.pdf Format de la ressource électronique : URL Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=55055 Réservation
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Code-barres Cote Support Localisation Section Disponibilité 15053-01 33.70 Livre Centre de documentation Photogrammétrie - Lasergrammétrie Disponible
Titre : Reconstruction of 3D building models from aerial images and maps Type de document : Monographie Auteurs : I. Süveg, Auteur Editeur : Delft : Netherlands Geodetic Commission NGC Année de publication : 2003 Collection : Netherlands Geodetic Commission Publications on Geodesy, ISSN 0165-1706 num. 53 Importance : 143 p. Format : 17 x 24 cm ISBN/ISSN/EAN : 978-90-6132-280-1 Note générale : Bibliographie Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Photogrammétrie numérique
[Termes IGN] arbre de décision
[Termes IGN] base de données urbaines
[Termes IGN] bibliothèque de formes
[Termes IGN] contour
[Termes IGN] fusion de données
[Termes IGN] image aérienne
[Termes IGN] modèle 3D de l'espace urbain
[Termes IGN] modélisation 3D
[Termes IGN] reconstruction 3D du bâti
[Termes IGN] segmentation
[Termes IGN] zone urbaineIndex. décimale : 33.30 Photogrammétrie numérique Résumé : (Auteur) The 3D reconstruction of buildings has numerous applications in areas that include urban planning, construction, environment, communication, transportation, energy and property management, tourism, and virtual tours of cities. In this thesis, the reconstruction of 3D building models from aerial images is addressed. The approach presented in this thesis integrates the aerial images analysis with information from a GIS database and domain knowledge.
The problem of automatic 3D building reconstruction has been a central research topic in computer vision and image understanding communities as well as in digital photogrammetry for many years. A variety of approaches has been suggested for the reconstruction of buildings from aerial images. Despite considerable research effort, there is no complete system that can reliably perform autonomous 3D building reconstruction in a wide variety of scene domains. This is particularly true in complex urban areas containing buildings with different shapes and roof types as well as in complicated underlying terrain. Of course, some progress has been made, but there is room for improvement. This improvement can be achieved by fusing multiple data sources and some a priori information.
In this project, largescale 2D GIS databases were used as additional information source. Combination of image data and map data turned out to improve the reliability of the reconstruction. Generic knowledge about the shape of the buildings is also incorporated in the system. Since most buildings can be described as an aggregation of simple building types, the knowledge about the problem domain can be represented in a building library containing simple building models. Therefore, a building library was defined containing the most common building primitives, such as flat roof, and different types of gable roofs.
The building reconstruction process was formulated as a multilevel hypothesis generation and verification scheme and it was implemented as a search tree. A method that can localize the buildings in images using map information has been developed. Also, a method for generating building hypotheses corresponding to the primitives defined in the building library has been developed. This implies stereo matching of image features (corners, lines) which correspond to map primitives and fitting of the building hypotheses to images.
A further contribution is the definition of a metric for evaluating the generated building hypotheses in order to select the one which best describes the image. The metric is based on the formulation of the mutual information between the building model and the images. Methods for the estimation of the mutual information from training samples were analyzed. This metric has been rigorously derived from information theory and does not require a priori information about the surface properties of the object and is robust with respect to variations of illumination. Also, no assumption about the shape of the objects are made. As result the method is quite general and may be used in a wide variety of applications.
The produced approach is able to meet most of the requirements of an automatic 3D building reconstruction system. The developed system has been used in urban and suburban areas to reconstruct buildings and showed good results. Experiments were carried out on two data sets with different characteristics. The system was able to reconstruct more than 80% of the buildings and the accuracy of the reconstruction is good enough for mapping purposes.Numéro de notice : 15043 Affiliation des auteurs : non IGN Thématique : IMAGERIE Nature : Monographie DOI : sans En ligne : https://ncgeo.nl/downloads/53Suveg.pdf Format de la ressource électronique : URL Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=55049 Réservation
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Code-barres Cote Support Localisation Section Disponibilité 15043-02 33.30 Livre Centre de documentation Photogrammétrie - Lasergrammétrie Disponible 15043-01 33.30 Livre Centre de documentation Photogrammétrie - Lasergrammétrie Disponible Fast precise GPS positioning in the presence of ionospheric delays / Dennis Odijk (2002)
Titre : Fast precise GPS positioning in the presence of ionospheric delays Type de document : Monographie Auteurs : Dennis Odijk, Auteur Editeur : Delft : Netherlands Geodetic Commission NGC Année de publication : 2002 Collection : Netherlands Geodetic Commission Publications on Geodesy, ISSN 0165-1706 num. 52 Importance : 242 p. Format : 16 x 24 cm ISBN/ISSN/EAN : 978-90-6132-278-8 Note générale : Bibliographie Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Géodésie spatiale
[Termes IGN] ambiguïté entière
[Termes IGN] correction ionosphérique
[Termes IGN] correction troposphérique
[Termes IGN] données GPS
[Termes IGN] interpolation
[Termes IGN] krigeage
[Termes IGN] mesurage de phase
[Termes IGN] méthode des moindres carrés
[Termes IGN] modèle de Gauss-Markov
[Termes IGN] modèle ionosphérique
[Termes IGN] modèle stochastique
[Termes IGN] propagation ionosphérique
[Termes IGN] propagation troposphérique
[Termes IGN] réfraction atmosphérique
[Termes IGN] résolution d'ambiguïté
[Termes IGN] signal GPS
[Termes IGN] station virtuelle
[Termes IGN] traitement de données GNSS
[Termes IGN] traitement du signalIndex. décimale : 30.61 Systèmes de Positionnement par Satellites du GNSS Résumé : (Auteur) This thesis deals about geodetic applications of the Global Positioning System (GPS), in which the position of the GPS receiver must be determined with cm precision. This requires a relative measurement setup, together with an advanced processing strategy based on observations of the carrierphase of the signal. To keep it economically interesting, this CPS technique should be based on relatively short time spans in which the satellite observations are collected. The key to precise positioning using short time spans is to take advantage of the integer property of the ambiguities of the phase observations in the processing.
The above procedure has been applied in a successful way for the last decade to applications in which the distance between the receivers is restricted to about 10 km (the socalled rapidstatic and realtime kinematic GPS techniques over short distances). Above this distance, it is known that certain errors in the GPS observations start to significantly bias the computed receiver position when they are not taken care of. The aim of this research therefore is to develop a processing procedure, taking into account the errors in GPS observations due to propagation of the signals through the ionosphere, the atmospheric layer above about 80 kill. Although other errors (due to troposphere and satellite orbit) are of relevance as well, the research is restricted to an improved modelling of the ionospheric error. since it is by far the largest error. For the other errors standard modelling techniques are applied in this research. Using the procedure, it should be possible to determine the desired receiver positions with cmprecision using a short tinle span. The research is restricted to GPS receivers with a mutual distance of a few hundred km (mediumdistance baselines), located in midlatitude regions.
To facilitate a modelling of the ionospheric error, using the theor ' y of atmospheric refraction it is possible to decompose this error into a firstorder effect, which contains the gross of the error, plus some higherorder effects and a term due to bending of the signal path. Under worstcase conditions. the firstorder term may range up to about 80 m (on the GPS L2 frequency), whereas the accumulated effect of higherorder and bending terms can be tip to 4 cm (for L2). For the future L5 frequency (from 2008) these effects are even larger. Fortunately, because of the relative setup and the assumed medium distances, it is proved for this research it is allowed to neglect the higherorder and bending errors.
In the procedure a stochastic modelling of the firstorder ionospheric errors (referred to as ionospheric delays) is chosen. This means that the ionospheric delays are not modelled as completely unknown parameters, but that stochastic prior information is incorporated by means of ionospheric pseudoobservations. This model is referred to as the ionosphereweighted model: The weight of the ionospheric information can be tuned by the a priori standard deviation of the pseudoobservations. When this standard deviation is chosen zero, the ionosphereweighted model reduces to the ionospherefixed model, which is the usual processing model for shortdistance baselines (for which the ionospheric delays may be neglected). On the other hand, with an infinitely large ionospheric standard deviation, the model will be equivalent to the ionospherefloat model, in which the ionospheric delays are assumed as completely unknown parameters. This latter model is closely related to the ionospherefree combination, for which it is known that it cannot be used to achieve fast positioning results. It is shown that the ionosphereweighted model is only suitable for fast ambiguity resolution (and consequently positioning), when the ionospheric standard deviation is small. This requires very precise a priori ionospheric information.
The developed procedure consists of three steps. It is required that a user collects CPS observations in the vicinity of a network of permanent GPS stations. In the first step, the observations at the network stations are processed simultaneously using the ionosphereweighted model. Since in this research the goal is precise positioning within the shortest time span possible, i.e. instantaneous or singleepoch positioning, it is required that the network data is also processed instantaneously. To make instantaneous resolution of the network ambiguities possible, the sample values of the ionospheric pseudoobservations are temporal predictions based on estimates of previous epochs. Test computations using a network with a station spacing of more than 100 km demonstrated that in this way high network ambiguity success rates (close to 100%) can be obtained. In the second step, precise ambiguityfixed network ionospheric delays are spatially interpolated at the approximate location of the user's receiver. In the procedure for this purpose the concept of virtual reference station (VRS) observations is used. In this concept the network estimates (ionospheric delays and other parameters) are transformed to VRS observations. which should correspond to the data a real receiver would have collected at the user's location. The processing of the user's observations relative to this VRS is the third step of the procedure. Because of the presence of possible residual ionospheric delays also in this step the ionosphereweighted model is applied. The difference with the application in the network processing is that the sample values of the pseudoobservations are now taken zero. and the ionospheric standard deviation is computed as a function of the distance to the closest real network station. Using this, test computations demonstrated that instantaneous ambiguity success rates of 90% are feasible. When the ionospherefixed model would be applied, the success rates would not be higher than about 60%.Numéro de notice : 13101 Affiliation des auteurs : non IGN Thématique : POSITIONNEMENT Nature : Monographie Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=54884 Réservation
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