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The Global ETD Search service is a free service for researchers
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Networked Digital Library of Theses and Dissertations.
Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
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Showing 321 to 330 of 339 (0.023 seconds)Spelling suggestions: "subject:"3dpose"" "subject:"4close""
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Relative Navigation of Micro Air Vehicles in GPS-Degraded EnvironmentsWheeler, David Orton 01 December 2017 (has links)
Most micro air vehicles rely heavily on reliable GPS measurements for proper estimation and control, and therefore struggle in GPS-degraded environments. When GPS is not available, the global position and heading of the vehicle is unobservable. This dissertation establishes the theoretical and practical advantages of a relative navigation framework for MAV navigation in GPS-degraded environments. This dissertation explores how the consistency, accuracy, and stability of current navigation approaches degrade during prolonged GPS dropout and in the presence of heading uncertainty. Relative navigation (RN) is presented as an alternative approach that maintains observability by working with respect to a local coordinate frame. RN is compared with several current estimation approaches in a simulation environment and in hardware experiments. While still subject to global drift, RN is shown to produce consistent state estimates and stable control. Estimating relative states requires unique modifications to current estimation approaches. This dissertation further provides a tutorial exposition of the relative multiplicative extended Kalman filter, presenting how to properly ensure observable state estimation while maintaining consistency. The filter is derived using both inertial and body-fixed state definitions and dynamics. Finally, this dissertation presents a series of prolonged flight tests, demonstrating the effectiveness of the relative navigation approach for autonomous GPS-degraded MAV navigation in varied, unknown environments. The system is shown to utilize a variety of vision sensors, work indoors and outdoors, run in real-time with onboard processing, and not require special tuning for particular sensors or environments. Despite leveraging off-the-shelf sensors and algorithms, the flight tests demonstrate stable front-end performance with low drift. The flight tests also demonstrate the onboard generation of a globally consistent, metric, and localized map by identifying and incorporating loop-closure constraints and intermittent GPS measurements. With this map, mission objectives are shown to be autonomously completed.
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Robust Optimization for Simultaneous Localization and Mapping / Robuste Optimierung für simultane Lokalisierung und KartierungSünderhauf, Niko 25 April 2012 (has links) (PDF)
SLAM (Simultaneous Localization And Mapping) has been a very active and almost ubiquitous problem in the field of mobile and autonomous robotics for over two decades. For many years, filter-based methods have dominated the SLAM literature, but a change of paradigms could be observed recently.
Current state of the art solutions of the SLAM problem are based on efficient sparse least squares optimization techniques. However, it is commonly known that least squares methods are by default not robust against outliers. In SLAM, such outliers arise mostly from data association errors like false positive loop closures. Since the optimizers in current SLAM systems are not robust against outliers, they have to rely heavily on certain preprocessing steps to prevent or reject all data association errors. Especially false positive loop closures will lead to catastrophically wrong solutions with current solvers. The problem is commonly accepted in the literature, but no concise solution has been proposed so far.
The main focus of this work is to develop a novel formulation of the optimization-based SLAM problem that is robust against such outliers. The developed approach allows the back-end part of the SLAM system to change parts of the topological structure of the problem\'s factor graph representation during the optimization process. The back-end can thereby discard individual constraints and converge towards correct solutions even in the presence of many false positive loop closures. This largely increases the overall robustness of the SLAM system and closes a gap between the sensor-driven front-end and the back-end optimizers. The approach is evaluated on both large scale synthetic and real-world datasets.
This work furthermore shows that the developed approach is versatile and can be applied beyond SLAM, in other domains where least squares optimization problems are solved and outliers have to be expected. This is successfully demonstrated in the domain of GPS-based vehicle localization in urban areas where multipath satellite observations often impede high-precision position estimates.
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| 323 |
Isomorphic Visualization and Understanding of the Commutativity of Multiplication: from multiplication of whole numbers to multiplication of fractionsMalaty, George 16 March 2012 (has links) (PDF)
No description available.
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| 324 |
Stereo Camera Calibration Accuracy in Real-time Car Angles Estimation for Vision Driver Assistance and Autonomous DrivingAlgers, Björn January 2018 (has links)
The automotive safety company Veoneer are producers of high end driver visual assistance systems, but the knowledge about the absolute accuracy of their dynamic calibration algorithms that estimate the vehicle’s orientation is limited. In this thesis, a novel measurement system is proposed to be used in gathering reference data of a vehicle’s orientation as it is in motion, more specifically the pitch and roll angle of the vehicle. Focus has been to estimate how the uncertainty of the measurement system is affected by errors introduced during its construction, and to evaluate its potential in being a viable tool in gathering reference data for algorithm performance evaluation. The system consisted of three laser distance sensors mounted on the body of the vehicle, and a range of data acquisition sequences with different perturbations were performed by driving along a stretch of road in Linköping with weights loaded in the vehicle. The reference data were compared to camera system data where the bias of the calculated angles were estimated, along with the dynamic behaviour of the camera system algorithms. The experimental results showed that the accuracy of the system exceeded 0.1 degrees for both pitch and roll, but no conclusions about the bias of the algorithms could be drawn as there were systematic errors present in the measurements. / Bilsäkerhetsföretaget Veoneer är utvecklare av avancerade kamerasystem inom förarassistans, men kunskapen om den absoluta noggrannheten i deras dynamiska kalibreringsalgoritmer som skattar fordonets orientering är begränsad. I denna avhandling utvecklas och testas ett nytt mätsystem för att samla in referensdata av ett fordons orientering när det är i rörelse, mer specifikt dess pitchvinkel och rollvinkel. Fokus har legat på att skatta hur osäkerheten i mätsystemet påverkas av fel som introducerats vid dess konstruktion, samt att utreda dess potential när det kommer till att vara ett gångbart alternativ för att samla in referensdata för evaluering av prestandan hos algoritmerna. Systemet bestod av tre laseravståndssensorer monterade på fordonets kaross. En rad mätförsök utfördes med olika störningar introducerade genom att köra längs en vägsträcka i Linköping med vikter lastade i fordonet. Det insamlade referensdatat jämfördes med data från kamerasystemet där bias hos de framräknade vinklarna skattades, samt att de dynamiska egenskaperna kamerasystemets algoritmer utvärderades. Resultaten från mätförsöken visade på att noggrannheten i mätsystemet översteg 0.1 grader för både pitchvinklarna och rollvinklarna, men några slutsatser kring eventuell bias hos algoritmerna kunde ej dras då systematiska fel uppstått i mätresultaten.
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Dräkt och pose i porträtt : En analys av posens fiktion och dräktens avbildning i tre porträtt föreställande Herman Wrangel (1584 - 1643)Bredberg, Eva January 2017 (has links)
This study is concerned with portraiture as a roleplay and a strategy to communicate the sitter´s identity to affect the viewer. Focusing on the sitter´s pose and the depiction of dress, the study examines three portraits between 1624 and the 1630s, representing Herman Wrangel (1584–1643), Field Marshal and Councilor of the Realm. The analysis is based on the concept, the fiction of the pose, developed by Harry Berger Jr. The idea of Theatricality discussed by Hanneke H Grootenboer´s is also used. The results show that dress, details of dress and the pose which are significant for the identity of the sitter are depicted with emphasis. Therefore, the dress and the pose have a key role in the depiction of the sitter acting his identity. The sitter acts before the artist and in the long run before the beholder. The portrait of the nobleman becomes a monologue for the beholder who can confirm the nobility´s role in society. / Uppsatsen handlar om hur porträttmåleri som ett rollspel och en strategi för förmedling av den avporträtterades identitet till betraktaren. Tre porträtt från perioden 1624–1630, föreställande Herman Wrangel (1584–1643) fältmarskalk och riksråd, har analyserats med fokus på den avporträtterades pose och dräktens avbildning med stöd i begreppet the fiction of the pose, baserat på Harry Berger Jr teori. Vidare används begreppet teatrikalitet, som det diskuteras av Hanneke H Grootenboer. Undersökningen visar att dräkt och dräktdetaljer samt poser som är betydelsefulla, för den avporträtterades identitet, framställs med emfas. Därmed spelar dräkten och posen en viktig roll i den avporträtterades framställan. Den avporträtterade agerar inför konstnären och i förlängningen inför betraktaren. Porträttet av adelsmannen blir en uppvisning, en monolog inför betraktaren som kan bekräfta adelsmannens roll i den sociala hierarkin.
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Presence through actions : theories, concepts, and implementationsKhan, Muhammad Sikandar Lal January 2017 (has links)
During face-to-face meetings, humans use multimodal information, including verbal information, visual information, body language, facial expressions, and other non-verbal gestures. In contrast, during computer-mediated-communication (CMC), humans rely either on mono-modal information such as text-only, voice-only, or video-only or on bi-modal information by using audiovisual modalities such as video teleconferencing. Psychologically, the difference between the two lies in the level of the subjective experience of presence, where people perceive a reduced feeling of presence in the case of CMC. Despite the current advancements in CMC, it is still far from face-to-face communication, especially in terms of the experience of presence. This thesis aims to introduce new concepts, theories, and technologies for presence design where the core is actions for creating presence. Thus, the contribution of the thesis can be divided into a technical contribution and a knowledge contribution. Technically, this thesis details novel technologies for improving presence experience during mediated communication (video teleconferencing). The proposed technologies include action robots (including a telepresence mechatronic robot (TEBoT) and a face robot), embodied control techniques (head orientation modeling and virtual reality headset based collaboration), and face reconstruction/retrieval algorithms. The introduced technologies enable action possibilities and embodied interactions that improve the presence experience between the distantly located participants. The novel setups were put into real experimental scenarios, and the well-known social, spatial, and gaze related problems were analyzed. The developed technologies and the results of the experiments led to the knowledge contribution of this thesis. In terms of knowledge contribution, this thesis presents a more general theoretical conceptual framework for mediated communication technologies. This conceptual framework can guide telepresence researchers toward the development of appropriate technologies for mediated communication applications. Furthermore, this thesis also presents a novel strong concept – presence through actions - that brings in philosophical understandings for developing presence- related technologies. The strong concept - presence through actions is an intermediate-level knowledge that proposes a new way of creating and developing future 'presence artifacts'. Presence- through actions is an action-oriented phenomenological approach to presence that differs from traditional immersive presence approaches that are based (implicitly) on rationalist, internalist views.
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| 327 |
3D Rekonstrukce historických míst z obrázků na Flickru / 3D Reconstruction of Historic Landmarks from Flickr PicturesŠimetka, Vojtěch January 2015 (has links)
Tato práce popisuje problematiku návrhu a vývoje aplikace pro rekonstrukci 3D modelů z 2D obrazových dat, označované jako bundle adjustment. Práce analyzuje proces 3D rekonstrukce a důkladně popisuje jednotlivé kroky. Prvním z kroků je automatizované získání obrazové sady z internetu. Je představena sada skriptů pro hromadné stahování obrázků ze služeb Flickr a Google Images a shrnuty požadavky na tyto obrázky pro co nejlepší 3D rekonstrukci. Práce dále popisuje různé detektory, extraktory a párovací algoritmy klíčových bodů v obraze s cílem najít nejvhodnější kombinaci pro rekonstrukci budov. Poté je vysvětlen proces rekonstrukce 3D struktury, její optimalizace a jak je tato problematika realizovaná v našem programu. Závěr práce testuje výsledky získané z implementovaného programu pro několik různých datových sad a porovnává je s výsledky ostatních podobných programů, představených v úvodu práce.
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| 328 |
Robust Optimization for Simultaneous Localization and MappingSünderhauf, Niko 19 April 2012 (has links)
SLAM (Simultaneous Localization And Mapping) has been a very active and almost ubiquitous problem in the field of mobile and autonomous robotics for over two decades. For many years, filter-based methods have dominated the SLAM literature, but a change of paradigms could be observed recently.
Current state of the art solutions of the SLAM problem are based on efficient sparse least squares optimization techniques. However, it is commonly known that least squares methods are by default not robust against outliers. In SLAM, such outliers arise mostly from data association errors like false positive loop closures. Since the optimizers in current SLAM systems are not robust against outliers, they have to rely heavily on certain preprocessing steps to prevent or reject all data association errors. Especially false positive loop closures will lead to catastrophically wrong solutions with current solvers. The problem is commonly accepted in the literature, but no concise solution has been proposed so far.
The main focus of this work is to develop a novel formulation of the optimization-based SLAM problem that is robust against such outliers. The developed approach allows the back-end part of the SLAM system to change parts of the topological structure of the problem\'s factor graph representation during the optimization process. The back-end can thereby discard individual constraints and converge towards correct solutions even in the presence of many false positive loop closures. This largely increases the overall robustness of the SLAM system and closes a gap between the sensor-driven front-end and the back-end optimizers. The approach is evaluated on both large scale synthetic and real-world datasets.
This work furthermore shows that the developed approach is versatile and can be applied beyond SLAM, in other domains where least squares optimization problems are solved and outliers have to be expected. This is successfully demonstrated in the domain of GPS-based vehicle localization in urban areas where multipath satellite observations often impede high-precision position estimates.
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| 329 |
Cooperative Navigation of Fixed-Wing Micro Air Vehicles in GPS-Denied EnvironmentsEllingson, Gary James 05 November 2019 (has links)
Micro air vehicles have recently gained popularity due to their potential as autonomous systems. Their future impact, however, will depend in part on how well they can navigate in GPS-denied and GPS-degraded environments. In response to this need, this dissertation investigates a potential solution for GPS-denied operations called relative navigation. The method utilizes keyframe-to-keyframe odometry estimates and their covariances in a global back end that represents the global state as a pose graph. The back end is able to effectively represent nonlinear uncertainties and incorporate opportunistic global constraints. The GPS-denied research community has, for the most part, neglected to consider fixed-wing aircraft. This dissertation enables fixed-wing aircraft to utilize relative navigation by accounting for their sensing requirements. The development of an odometry-like, front-end, EKF-based estimator that utilizes only a monocular camera and an inertial measurement unit is presented. The filter uses the measurement model of the multi-state-constraint Kalman filter and regularly performs relative resets in coordination with keyframe declarations. In addition to the front-end development, a method is provided to account for front-end velocity bias in the back-end optimization. Finally a method is presented for enabling multiple vehicles to improve navigational accuracy by cooperatively sharing information. Modifications to the relative navigation architecture are presented that enable decentralized, cooperative operations amidst temporary communication dropouts. The proposed framework also includes the ability to incorporate inter-vehicle measurements and utilizes a new concept called the coordinated reset, which is necessary for optimizing the cooperative odometry and improving localization. Each contribution is demonstrated through simulation and/or hardware flight testing. Simulation and Monte-Carlo testing is used to show the expected quality of the results. Hardware flight-test results show the front-end estimator performance, several back-end optimization examples, and cooperative GPS-denied operations.
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| 330 |
Enabling Autonomous Operation of Micro Aerial Vehicles Through GPS to GPS-Denied TransitionsJackson, James Scott 11 November 2019 (has links)
Micro aerial vehicles and other autonomous systems have the potential to truly transform life as we know it, however much of the potential of autonomous systems remains unrealized because reliable navigation is still an unsolved problem with significant challenges. This dissertation presents solutions to many aspects of autonomous navigation. First, it presents ROSflight, a software and hardware architure that allows for rapid prototyping and experimentation of autonomy algorithms on MAVs with lightweight, efficient flight control. Next, this dissertation presents improvments to the state-of-the-art in optimal control of quadrotors by utilizing the error-state formulation frequently utilized in state estimation. It is shown that performing optimal control directly over the error-state results in a vastly more computationally efficient system than competing methods while also dealing with the non-vector rotation components of the state in a principled way. In addition, real-time robust flight planning is considered with a method to navigate cluttered, potentially unknown scenarios with real-time obstacle avoidance. Robust state estimation is a critical component to reliable operation, and this dissertation focuses on improving the robustness of visual-inertial state estimation in a filtering framework by extending the state-of-the-art to include better modeling and sensor fusion. Further, this dissertation takes concepts from the visual-inertial estimation community and applies it to tightly-coupled GNSS, visual-inertial state estimation. This method is shown to demonstrate significantly more reliable state estimation than visual-inertial or GNSS-inertial state estimation alone in a hardware experiment through a GNSS-GNSS denied transition flying under a building and back out into open sky. Finally, this dissertation explores a novel method to combine measurements from multiple agents into a coherent map. Traditional approaches to this problem attempt to solve for the position of multiple agents at specific times in their trajectories. This dissertation instead attempts to solve this problem in a relative context, resulting in a much more robust approach that is able to handle much greater intial error than traditional approaches.
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