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Automatic object extraction from airborne laser scanning point clouds for digital base map production / Elyta Widyaningrum (2021)  

Public Titre : Automatic object extraction from airborne laser scanning point clouds for digital base map production Type de document : Thèse/HDR Auteurs : Elyta Widyaningrum, Auteur Editeur : Delft [Pays-Bas] : Delft University of Technology Année de publication : 2021 Note générale : bibliographie Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Applications photogrammétriques [Termes IGN] axe médian [Termes IGN] chaîne de traitement [Termes IGN] détection d'objet [Termes IGN] détection du bâti [Termes IGN] données lidar [Termes IGN] données localisées 3D [Termes IGN] extraction du réseau routier [Termes IGN] image aérienne [Termes IGN] orthoimage [Termes IGN] semis de points [Termes IGN] squelettisation [Termes IGN] transformation de Hough [Termes IGN] vectorisation Résumé : (auteur) A base map provides essential geospatial information for applications such as urban planning, intelligent transportation systems, and disaster management. Buildings and roads are the main ingredients of a base map and are represented by polygons. Unfortunately, manually delineating their boundaries from remote sensing data is time consuming and labour intensive. Airborne laser scanning (ALS) point clouds provide dense and accurate 3D positional information. Automatic extraction of buildings and roads from 3D point clouds is challenging because of their irregular shapes, occlusions in the data, and irregularity of ALS point clouds. This study focuses on two particular objectives: (i) accurate classification of a large volume of ALS 3D point clouds; and (ii) smooth and accurate building and road outline extraction. To achieve the classification objective, we perform point-wise deep learning to classify an ALS point cloud of a complex urban scene in Surabaya, Indonesia. The point cloud is colored by airborne orthophotos. Training data is obtained from an existing 2D topographic base map by a semi-automatic method proposed in this research. A dynamic-graph convolutional neural network is used to classify the point cloud into four classes: bare land, trees, buildings, and roads. We investigate effective input feature combinations for outdoor point cloud classification. A highly acceptable classification result of 91.8% overall accuracy is achieved when using the full combination of RGB color and LiDAR features. To address the objective of outline extraction, we propose building and road outline extraction methods that run directly on ALS point cloud data. For accurate and smooth building outline extraction, we propose two different methods. First, we develop the ordered Hough transform (OHT), which is an extension of the traditional Hough transform, by explicitly incorporating the sequence of points to form the outline. Second, we propose a new method based on Medial Axis Transform (MAT) skeletons which takes advantage of the skeleton points to detect building corners. The OHT method is resistant to noise but it requires prior knowledge on a building’s main directions. On the contrary, the MAT-based method does not require such orientation initialization but is more sensitive to noise on building edges. We compare the results of our building outline extraction methods to an existing RANSAC-based method, in terms of geometric accuracy, completeness of building corners, and computation time, and demonstrate that the MAT-based approach has the highest geometric accuracy, results in more complete building corners, and is slightly faster than other methods. For road network extraction, we develop a method based on skeletonization, which results in complete and continuous road centerlines and boundaries. In our study area, several roads are disrupted and disconnected due to trees. We design a tree-constrained approach to fill road gaps and integrate road width estimated from a medial axis algorithm. Comparison to reference data shows that the proposed method is able to extract almost all existing roads in the study area, and even detects roads that were not present in the reference due to human errors. We conclude that our object extraction methods enable a complete automatic procedure, extracting more accurate building and road outlines from ALS point cloud data. This contributes to a higher automation readiness level for a faster and cheaper base map production. Numéro de notice : 17664 Affiliation des auteurs : non IGN Thématique : IMAGERIE/INFORMATIQUE Nature : Thèse étrangère Note de thèse : PhD thesis : Sciences : TU Delft: 2021 Date de publication en ligne : 10/03/2021 En ligne : https://doi.org/10.4233/uuid:8900fac8-a76c-482a-b280-e1758783b5b3 Format de la ressource électronique : URL Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=97984

High accuracy terrestrial positioning based on time delay and carrier phase using wideband radio signals / Han Dun (2021)  

Public Titre : High accuracy terrestrial positioning based on time delay and carrier phase using wideband radio signals Type de document : Thèse/HDR Auteurs : Han Dun, Auteur Editeur : Delft [Pays-Bas] : Delft University of Technology Année de publication : 2021 Format : 21 x 30 cm ISBN/ISSN/EAN : 978-94-6384-258-7 Note générale : bibliographie Thèse présentée en vue de l'obtention du Doctorat de l'Université de Delft Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Traitement du signal [Termes IGN] centre de phase [Termes IGN] correction du trajet multiple [Termes IGN] interruption du signal [Termes IGN] méthode du maximum de vraisemblance (estimation) [Termes IGN] phase [Termes IGN] précision du positionnement [Termes IGN] signal GNSS [Termes IGN] zone urbaine Index. décimale : THESE Thèses et HDR Résumé : (auteur) Accurate position solutions are in high demand for many emerging applications. Global navigation satellite systems (GNSS), however, may not meet the required positioning performance, especially in urban environments, due to multipath and weak received power of the GNSS signal that can be easily blocked by surrounding objects. To achieve a high ranging precision and improve resolvability of unwanted reflections in urban areas, a large signal bandwidth is required. In this thesis, a terrestrial positioning system using a wideband radio signal is developed as a complement to the existing GNSS, which can provide a better ranging accuracy and higher received signal power, compared to GNSS. In the terrestrial positioning system presented in this thesis, a wideband ranging signal is implemented by means of a multiband orthogonal frequency division multiplexing (OFDM) signal. All transmitters are synchronized by time and frequency reference signals, which are optically distributed through the white-rabbit precision time protocol (WR-PTP). Like in GNSS, the to-be-positioned receiver is not synchronized to the transmitters. Positioning takes place through range measurements between a number of transmitters and the receiver. Time delay and carrier phase are to be estimated from the received radio signal, which propagated through a multipath channel. This estimation is done on the basis of the channel frequency response and using the maximum likelihood principle. To determine whether or not reflections need to be considered in the estimation model, a measure of dependence is introduced to evaluate the change of the precision (i.e., variance), and the measure of bias is introduced to assess the bias of the estimator when the reflection is not considered. Also, a methodology is proposed for sparsity-promoting ranging signal design in this thesis. Based on a multiband OFDM signal, ranging signal design comes to sparsely select as few signal bands as possible. Using fewer signal bands for ranging leads to less computational complexity in time delay and carrier phase estimation, while the ranging performance can still benefit from a large virtual signal bandwidth, which is defined by the entire bandwidth between the two signal bands at the spectral edges. It is proposed to use the Cramér-Rao lower bound (CRLB) of time delay estimation, the measure of dependence, and the measure of bias as constraints in ranging performance, and formulate an optimization problem to design a sparse multiband signal. Note de contenu : 1- Introduction 2- Multiband OFDM signal model 3- Time delay estimation 4- Carrier phase estimation 5- Signal design for positioning 6- Positioning models 7- Experimental results 8- Conclusions and recommendations Numéro de notice : 28694 Affiliation des auteurs : non IGN Thématique : POSITIONNEMENT Nature : Thèse étrangère Note de thèse : Thèse de Doctorat : Mathematical Geodesy and Positioning : Delft : 2021 DOI : 10.4233/uuid:98a7f072-7423-4a23-ac9b-8b88540c260d En ligne : https://doi.org/10.4233/uuid:98a7f072-7423-4a23-ac9b-8b88540c260d Format de la ressource électronique : URL Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=100361

Geospatial data on the web / Linda Van Den Brink (2018)  

Public Titre : Geospatial data on the web Type de document : Thèse/HDR Auteurs : Linda Van Den Brink, Auteur ; Jantien E. Stoter, Directeur de thèse Editeur : Delft : Netherlands Geodetic Commission NGC Année de publication : 2018 Autre Editeur : Delft [Pays-Bas] : Delft University of Technology Collection : Netherlands Geodetic Commission Publications on Geodesy, ISSN 0165-1706 Importance : 232 p. Format : 21 x 30 cm Note générale : bibliographie Dissertation for the purpose of obtaining the degree of doctor at Delft University of Technology Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Géomatique web [Termes IGN] accès aux données localisées [Termes IGN] acquisition de données [Termes IGN] CityGML [Termes IGN] diffusion de données [Termes IGN] données hétérogènes [Termes IGN] données localisées [Termes IGN] données multisources [Termes IGN] données topographiques [Termes IGN] harmonisation des données [Termes IGN] interopérabilité [Termes IGN] outil d'aide à la décision [Termes IGN] RDF [Termes IGN] recherche d'information géographique [Termes IGN] réutilisation des données [Termes IGN] similitude sémantique [Termes IGN] web des données Résumé : (auteur) Geospatial data is an increasingly important information asset for decisionmaking, from simple every day decisions like where to park your car, to national and international policy on topics like infrastructure and environment. Because of the location aspect, geospatial data is often the linking pin between different datasets and therefore important for data integration. A lot of geospatial data is created, for example, as part of governmental processes and nowadays, also disseminated as open data, traditionally through "Spatial data infrastructures" (SDIs). There is a lot of potential for reusing this data in other domains than the domain and use case for which it was originally created. My main research question was: "How to reuse geospatial data, from different, heterogeneous sources, via the web across communities?". Several aspects of data dissemination must be addressed before open data is actually in a good position for getting reused. These aspects have been coined the "FAIR principles": findability, accessibility, interoperability, and reusability. Note de contenu : 1- Introduction, research questions and methodology 2- Definition and establishment of a national 3D standard 3- Semantic Harmonisation 4- Geospatial Linked Data 5- Web of Data 6- Discussion, Conclusion and Future work Numéro de notice : 21836 Affiliation des auteurs : non IGN Autre URL associée : https://repository.tudelft.nl/islandora/object/uuid%3Aa0bd364d-f101-4337-91c5-92038b2a6d56?collection=research Thématique : GEOMATIQUE/SOCIETE NUMERIQUE Nature : Thèse étrangère Note de thèse : PhD thesis : 3D Geo-Information : TU Delft : 2018 DOI : 10.4233/uuid:a0bd364d-f101-4337-91c5-92038b2a6d56 En ligne : https://www.ncgeo.nl/index.php/en/publicatiesgb/publications-on-geodesy/item/278 [...] Format de la ressource électronique : URL Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=91364

Level of detail in 3D city models / Filip Biljecki (2017)  

Public Titre : Level of detail in 3D city models Type de document : Thèse/HDR Auteurs : Filip Biljecki, Auteur ; Jantien E. Stoter, Auteur ; Hugo Ledoux, Auteur Editeur : Delft [Pays-Bas] : Delft University of Technology Année de publication : 2017 Note générale : bibliographie Doctoral dissertation, Delft university of technology Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Bases de données localisées [Termes IGN] analyse de sensibilité [Termes IGN] bâtiment [Termes IGN] CityGML [Termes IGN] erreur en position [Termes IGN] modèle 3D de l'espace urbain [Termes IGN] niveau de détail [Termes IGN] propagation d'erreur [Termes IGN] SIG 3D [Termes IGN] spécification Résumé : (auteur) The concept of level of detail (LOD) describes the content of 3D city models and it plays an essential role during their life cycle. On one hand it comes akin to the concepts of scale in cartography and LOD in computer graphics, on the other hand it is a standalone concept that requires attention. LOD has an influence on tendering and acquisition, and it has a hand in storage, maintenance, and application aspects. However, it has not been significantly researched, and this PhD thesis fills this void. This thesis reviews dozens of current LOD standards, revealing that most practitioners consider the LOD to be comprised solely of the geometric detail of data and there are disparate views on the concept as a whole. However, the research suggests that the LOD encompasses additional metrics, such as semantics and texture. The thesis formalises the concept, enabling integration and comparison of current LOD standards. The established framework may be applied to cartography and to different forms of 3D geoinformation such as point clouds. Following the formalised concept, a new LOD specification is presented improving the LOD concept in the current OGC CityGML 2.0 standard, a prominent norm in the 3D GIS industry. The specification introduces 16 LODs for buildings that are shaped after analysing the capabilities of acquisition techniques and a large number of real-world datasets. The improved LOD specification may be integrated in product portfolios and tenders, preventing misunderstandings between stakeholders, and as a better language for communicating the specifics of a dataset to be acquired. The specification also considers different approaches to realise the data. Such geometric references result in dozens of different variants of the same LOD.3D data according to the LOD specification was generated using a procedural modelling engine that was developed over the course of the research. The engine is capable of producing 3D city models in a large number of different variants and according to the CityGML standard. The thesis also catalogues the many different ways to create 3D city models. A prominent technique for producing data in a different LOD is generalisation, i.e. simplifying a 3D city model. The inverse---augmenting the LOD of a dataset---has not been researched to a great extent, and this thesis gives an overview of the topic. This research demonstrates that it is possible to generate 3D city models without elevation measurements, inherently augmenting the LOD of coarser data (2D footprints). The method relies on machine learning: several attributes found in 2D datasets may hint at the height of a building, thus enabling extrusion and creating 3D city models suited for several applications.Some acquisition techniques may result in multi-LOD datasets, and nowadays there are some regions represented in different, independent datasets. However, it was found that possibilities to link such data are deficient. The lack of linking mechanisms inhibits acquisition, storage, and maintenance of multi-LOD data. Two methods for linking features across two or more LODs have been developed resulting in an increased consistency of multi-LOD datasets. The first method links matching geometries across multiple LODs, while the second method establishes a 4D data structure in which the LOD is modelled as the fourth (spatial) dimension.It is often believed that the more detailed 3D data the better. However, similarly as in computer graphics, dealing with data at fine LODs comes at a cost: such datasets are harder to obtain, their storage footprint is large, and their usage within a spatial analysis may be slow. Scarce research has been dedicated to investigating whether an increase in the LOD of the data brings a comparably significant increase in benefits when the data is used in a spatial analysis.First, an analysis using real-world multi-LOD data was carried out. Different LODs of spatial data covering the Netherlands was used in a spatial analysis to refine population maps, obtaining different results for each LOD. However, several problems are exposed, revealing that using real data for such investigations is not optimal.The remainder of the research focuses on using procedurally generated data for such experiments. Synthetic data in several different LODs has been generated and employed for four spatial analyses (estimation of the building shadow, envelope area, volume, and solar irradiation). The experiments result in different conclusions. Finer LODs usually bring some improvement to the quality of the spatial analysis, but not always and such may be negligible. The results of the experiments ultimately depend on the spatial analysis that is considered. The varying results between different spatial analyses make each of them unique. Furthermore, the benefit a finer LOD brings to a spatial analysis is not always clear and easily measurable. In short, striving to produce data at finer LODs may please the eye, but this is not always counter-balanced in the benefit it brings to a spatial analysis.A further addition to the equation above is that when realised, 3D city models are unavoidably burdened with acquisition errors. An error propagation analysis was performed by disturbing the procedurally generated datasets with a range of simulated positional errors. Comparisons have been made between the intentionally degraded datasets and their error-free counterparts, thus obtaining the magnitude of uncertainty the positional errors cause in a spatial analysis. Based on these experiments, several findings are discovered, most importantly:1. How the LODs are realised (which geometric references are used) has a larger influence than the LOD. A coarse LOD produced with a favourable geometric reference may yield better results than a finer LOD realised with an unfavourable reference.2. Positional errors considerably affect spatial analyses. The effect is comparable across similar LODs. Simpler LODs are sligthly less affected by positional errors, but they may contain a large systematic error.3. Errors induced in the acquisition process generally cancel out the improvement provided by finer LODs. The main conclusion is that in the considered spatial analyses the positional error has a significantly higher impact than the LOD. As a consequence, it is suggested that it is pointless to acquire geoinformation at a fine LOD if the acquisition method is not accurate, and instead it is advised to focus on the improvement of accuracy of the data. The thesis proposes additional research for future work. For example, since this research focuses specifically on 3D building models, it would be worth extending the research to other urban features such as roads and vegetation. Furthermore, quality control in 3D GIS does not encompass the evaluation of the LOD of data. Hence integration of the LOD in quality standards should be a priority for future work. Note de contenu : 1- Introduction 2- Background 3- Formalisation of LOD 4- Designing an LOD specification for buildings 5- Variants of LODs 6- Realisation of the specification 7- Generating 3D city models without elevation data 8- Managing multi-LOD data 9- Influence of LOD on spatial analyses (I) 10- Influence of LOD on spatial analyses (II) 11- Sensitivity of LOD to positional errors 12- Combining LOD and positional errors 13- Conclusions and future prospects Numéro de notice : 17541 Affiliation des auteurs : non IGN Thématique : GEOMATIQUE Nature : Thèse étrangère Note de thèse : Doctoral dissertation : : Delft university of technology : 2017 DOI : 10.4233/uuid:f12931b7-5113-47ef-bfd4-688aae3be248 En ligne : https://repository.tudelft.nl/islandora/object/uuid%3Af12931b7-5113-47ef-bfd4-68 [...] Format de la ressource électronique : URL Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=91250

Estimation of slack tide using GPS measurements on a buoy / M. Valk (2011)    

Public Titre : Estimation of slack tide using GPS measurements on a buoy : A case study on buoy 18 in the Schelde Estuary Type de document : Mémoire Auteurs : M. Valk, Auteur Editeur : Delft [Pays-Bas] : Delft University of Technology Année de publication : 2011 Importance : 136 p. Format : 21 x 30 cm Note générale : bibliographie Master of Science Thesis for obtaining the degree of Master of Science in Geomatics Engineering at Delft University of Technology Langues : Anglais (eng) Descripteur : [Termes IGN] Belgique [Termes IGN] bouée [Termes IGN] données GPS [Termes IGN] estuaire [Termes IGN] marée océanique [Termes IGN] Pays-Bas [Termes IGN] rivière Index. décimale : MX Mémoires divers Résumé : (auteur) In this thesis, a method is developed to estimate the moment of slack tide based on GPS measurements on a buoy. The moment of slack tide is the very moment the tidal current changes direction. The method is applied in the Schelde Estuary in the Netherlands. An estuary is the transition between two distinct water bodies: a river and a sea. Estuaries are very important as a transport link and a source of food. Interventions in the estuary bathymetry, like dredging, can have severe impact on the hydraulic behavior of the estuary. Knowledge of the physical phenomena that determine the tidal flow is important as they influence the environment of an estuary in many ways. One of the key parameters in tidal propagation is the phase lag, which is the difference in time between high or low water and the subsequent moment of slack. The main objective of this thesis is to estimate the moment of slack tide based on GPS measurements on a buoy ultimately with an accuracy in the order of 5-10 minutes. The buoy, which is used as an aid to navigation, is floating on the water and tied to the sea floor by a heavy anchor chain. In order to achieve this goal it is necessary to: investigate the performance of different GPS receivers in combination with different antennas and operating modes; analyze the motion of the buoy during several tidal cycles; develop a method to estimate the moment of slack tide based on GPS measurements on a buoy; and, investigate whether the results could be further improved by employing a Kalman filter that combines knowledge about the dynamics of the buoy and series of measurements over time as opposed to a single epoch slack tide estimation. […] Note de contenu : 1- Introduction 2- Background 3- Materials and methods 4- Results and discussion 5- Conclusions and Recommendations Numéro de notice : 14867 Affiliation des auteurs : non IGN Thématique : POSITIONNEMENT Nature : Mémoire masters divers En ligne : http://resolver.tudelft.nl/uuid:11a3bbc4-5013-4833-871d-1035fca04636 Format de la ressource électronique : URL Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=75856

Documents numériques

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Variable-scale Geo-information / Martijn Meijers (2011)  

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Integer GPS-ambiguity estimation without the receiver-satellite geometry / N.F. Jonkman (1998)

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Publications LGR 1996 / Delft geodetic computing (1997)

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Publications 1995 [of the Delft geodetic computing centre] / Delft university of technology (1996)

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Publications 1994 [of the Delft geodetic computing centre] / Delft university of technology (1995)

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A recursive procedure for computation and quality control of GPS differential corrections / X. Jin (1995)

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Taylor expansion of GPS observations equations / X. Jin (1995)

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Dynamic GPS height determination in the decimeter level for bathymetric applications / Robert Lemmens (1993)

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Modeling the ionosphere for an active control network of GPS stations / Y. Georgiadiou (1993)

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Publications 1992 [of the Delft geodetic computing centre] / Delft university of technology (1993)

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