10 research outputs found
Metrological characterization of a vision-based system for relative pose measurements with fiducial marker mapping for spacecrafts
An improved approach for the measurement of the relative pose between a target and a chaser spacecraft is presented. The selected method is based on a single camera, which can be mounted on the chaser, and a plurality of fiducial markers, which can be mounted on the external surface of the target. The measurement procedure comprises of a closed-form solution of the Perspective from n Points (PnP) problem, a RANdom SAmple Consensus (RANSAC) procedure, a non-linear local optimization and a global Bundle Adjustment refinement of the marker map and relative poses. A metrological characterization of the measurement system is performed using an experimental set-up that can impose rotations combined with a linear translation and can measure them. The rotation and position measurement errors are calculated with reference instrumentations and their uncertainties are evaluated by the Monte Carlo method. The experimental laboratory tests highlight the significant improvements provided by the Bundle Adjustment refinement. Moreover, a set of possible influencing physical parameters are defined and their correlations with the rotation and position errors and uncertainties are analyzed. Using both numerical quantitative correlation coefficients and qualitative graphical representations, the most significant parameters for the final measurement errors and uncertainties are determined. The obtained results give clear indications and advice for the design of future measurement systems and for the selection of the marker positioning on a satellite surface
Indoor Mapping and Reconstruction with Mobile Augmented Reality Sensor Systems
Augmented Reality (AR) ermöglicht es, virtuelle, dreidimensionale Inhalte direkt
innerhalb der realen Umgebung darzustellen. Anstatt jedoch beliebige virtuelle
Objekte an einem willkürlichen Ort anzuzeigen, kann AR Technologie auch genutzt
werden, um Geodaten in situ an jenem Ort darzustellen, auf den sich die Daten
beziehen. Damit eröffnet AR die Möglichkeit, die reale Welt durch virtuelle, ortbezogene
Informationen anzureichern. Im Rahmen der vorliegenen Arbeit wird diese
Spielart von AR als "Fused Reality" definiert und eingehend diskutiert.
Der praktische Mehrwert, den dieses Konzept der Fused Reality bietet, lässt sich
gut am Beispiel seiner Anwendung im Zusammenhang mit digitalen Gebäudemodellen
demonstrieren, wo sich gebäudespezifische Informationen - beispielsweise der
Verlauf von Leitungen und Kabeln innerhalb der Wände - lagegerecht am realen
Objekt darstellen lassen. Um das skizzierte Konzept einer Indoor Fused Reality
Anwendung realisieren zu können, müssen einige grundlegende Bedingungen erfüllt
sein. So kann ein bestimmtes Gebäude nur dann mit ortsbezogenen Informationen
augmentiert werden, wenn von diesem Gebäude ein digitales Modell verfügbar ist.
Zwar werden größere Bauprojekt heutzutage oft unter Zuhilfename von Building
Information Modelling (BIM) geplant und durchgeführt, sodass ein digitales Modell
direkt zusammen mit dem realen Gebäude ensteht, jedoch sind im Falle älterer
Bestandsgebäude digitale Modelle meist nicht verfügbar. Ein digitales Modell eines
bestehenden Gebäudes manuell zu erstellen, ist zwar möglich, jedoch mit großem
Aufwand verbunden. Ist ein passendes Gebäudemodell vorhanden, muss ein AR
Gerät außerdem in der Lage sein, die eigene Position und Orientierung im Gebäude
relativ zu diesem Modell bestimmen zu können, um Augmentierungen lagegerecht
anzeigen zu können.
Im Rahmen dieser Arbeit werden diverse Aspekte der angesprochenen Problematik
untersucht und diskutiert. Dabei werden zunächst verschiedene Möglichkeiten
diskutiert, Indoor-Gebäudegeometrie mittels Sensorsystemen zu erfassen. Anschließend
wird eine Untersuchung präsentiert, inwiefern moderne AR Geräte, die
in der Regel ebenfalls über eine Vielzahl an Sensoren verfügen, ebenfalls geeignet
sind, als Indoor-Mapping-Systeme eingesetzt zu werden. Die resultierenden Indoor
Mapping Datensätze können daraufhin genutzt werden, um automatisiert
Gebäudemodelle zu rekonstruieren. Zu diesem Zweck wird ein automatisiertes,
voxel-basiertes Indoor-Rekonstruktionsverfahren vorgestellt. Dieses wird außerdem
auf der Grundlage vierer zu diesem Zweck erfasster Datensätze mit zugehörigen
Referenzdaten quantitativ evaluiert. Desweiteren werden verschiedene
Möglichkeiten diskutiert, mobile AR Geräte innerhalb eines Gebäudes und des zugehörigen
Gebäudemodells zu lokalisieren. In diesem Kontext wird außerdem auch
die Evaluierung einer Marker-basierten Indoor-Lokalisierungsmethode präsentiert.
Abschließend wird zudem ein neuer Ansatz, Indoor-Mapping Datensätze an den
Achsen des Koordinatensystems auszurichten, vorgestellt
Autonomous Navigation of Distributed Spacecraft using Graph-based SLAM for Proximity Operations in Small Celestial Bodies
Establishment of a sustainable human presence beyond the cislunar space is a major milestone for mankind. Small celestial bodies (SCBs) like asteroids are known to contain valuable natural resources necessary for the development of space assets essential to the accomplishment of this goal. Consequently, future robotic spacecraft missions to SCBs are envisioned with the objective of commercial in-situ resource utilization (ISRU). In mission design, there is also an increasing interest in the utilization of the distributed spacecraft, to benefit from specialization and redundancy. The ability of distributed spacecraft to navigate autonomously in the proximity of a SCB is indispensable for the successful realization of ISRU mission objectives. Quasi-autonomous methods currently used for proximity navigation require extensive ground support for mapping and model development, which can be an impediment for large scale multi-spacecraft ISRU missions in the future.
It is prudent to leverage the advances in terrestrial robotic navigation to investigate the development of novel methods for autonomous navigation of spacecraft. The primary objective of the work presented in this thesis is to evaluate the feasibility and investigate the development of methods based on graph-based simultaneous localization and mapping (SLAM), a popular algorithm used in terrestrial autonomous navigation, for the autonomous navigation of distributed spacecraft in the proximity of SCBs. To this end, recent research in graph-based SLAM is extensively studied to identify strategies used to enable multi-agent navigation. The spacecraft navigation requirement is formulated as a graph-based SLAM problem using metric GraphSLAM or topometric graph-based SLAM. Techniques developed based on the identified strategies namely, map merging, inter-spacecraft measurements and relative localization are then applied to this formulation to enable distributed spacecraft navigation. In each case, navigation is formulated in terms of its application to a proximity operation scenario that best suits the multi-agent navigation technique.
Several challenges related to the application of graph-based SLAM for spacecraft navigation, such as computational cost and illumination variation are also identified and addressed in the development of these methods. Experiments are performed using simulated models of asteroids and spacecraft dynamics, comparing the estimated states of the spacecraft and landmarks to the assumed true states. The results from the experiments indicate a consistent and robust state determination process, suggesting the suitability of the application of multi-agent navigation techniques to graph-based SLAM for enabling the autonomous navigation of distributed spacecraft near SCBs
The 25th Annual Precise Time and Time Interval (PTTI) Applications and Planning Meeting
Papers in the following categories are presented: recent developments in rubidium, cesium, and hydrogen-based frequency standards, and in cryogenic and trapped-ion technology; international and transnational applications of precise time and time interval (PTTI) technology with emphasis on satellite laser tracking networks, GLONASS timing, intercomparison of national time scales and international telecommunication; applications of PTTI technology to the telecommunications, power distribution, platform positioning, and geophysical survey industries; application of PTTI technology to evolving military communications and navigation systems; and dissemination of precise time and frequency by means of GPS, GLONASS, MILSTAR, LORAN, and synchronous communications satellites
Proceedings of the Eleventh Annual Precise Time and Time Interval (PTTI) Application and Planning Meeting
Thirty eight papers are presented addressing various aspects of precise time and time interval applications. Areas discussed include: past accomplishments; state of the art systems; new and useful applications, procedures, and techniques; and fruitful directions for research efforts
International VLBI Service for Geodesy and Astrometry 2008 Annual Report
This volume of reports is the 2008 Annual Report of the International VLBI Service for Geodesy and Astrometry (IVS). The individual reports were contributed by VLBI groups in the international geodetic and astrometric community who constitute the components of IVS. The 2008 Annual Report documents the work of these IVS components over the period January 1, 2008 through December 31, 2008. The reports document changes, activities, and progress of the IVS. The entire contents of this Annual Report also appear on the IVS Web site at http://ivscc.gsfc.nasa.gov/publications/ar2008
Abstracts on Radio Direction Finding (1899 - 1995)
The files on this record represent the various databases that originally composed the CD-ROM issue of "Abstracts on Radio Direction Finding" database, which is now part of the Dudley Knox Library's Abstracts and Selected Full Text Documents on Radio Direction Finding (1899 - 1995) Collection. (See Calhoun record https://calhoun.nps.edu/handle/10945/57364 for further information on this collection and the bibliography).
Due to issues of technological obsolescence preventing current and future audiences from accessing the bibliography, DKL exported and converted into the three files on this record the various databases contained in the CD-ROM.
The contents of these files are:
1) RDFA_CompleteBibliography_xls.zip [RDFA_CompleteBibliography.xls: Metadata for the complete bibliography, in Excel 97-2003 Workbook format; RDFA_Glossary.xls: Glossary of terms, in Excel 97-2003 Workbookformat; RDFA_Biographies.xls: Biographies of leading figures, in Excel 97-2003 Workbook format];
2) RDFA_CompleteBibliography_csv.zip [RDFA_CompleteBibliography.TXT: Metadata for the complete bibliography, in CSV format; RDFA_Glossary.TXT: Glossary of terms, in CSV format; RDFA_Biographies.TXT: Biographies of leading figures, in CSV format];
3) RDFA_CompleteBibliography.pdf: A human readable display of the bibliographic data, as a means of double-checking any possible deviations due to conversion
GSI Scientific Report 2009 [GSI Report 2010-1]
Displacement design response spectrum is an essential component for the currently-developing displacement-based seismic design and assessment procedures. This paper proposes a new and simple method for constructing displacement design response spectra on soft soil sites. The method takes into account modifications of the seismic waves by the soil layers, giving due considerations to factors such as the level of bedrock shaking, material non-linearity, seismic impedance contrast at the interface between soil and bedrock, and plasticity of the soil layers. The model is particularly suited to applications in regions with a paucity of recorded strong ground motion data, from which empirical models cannot be reliably developed