Vision-based Navigation Using Landmark Recognition for Unmanned Aerial Vehicles

This thesis describes a new approach for a vision-based positioning system for Un- manned Aerial Vehicles using a recognition method based on known, robust geo- graphic landmarks. Landmarks are used to calculate a position estimate in a global coordinate frame without requiring external signals, such as GPS. Absolute systems are of interest as they provide a redundant positioning system, allow UAVs to oper- ate when GPS-denied and can enable high-precision landings for spacecraft. The core challenge with vision-based absolute positioning is recognition of land- marks. Most abundant landmarks, such as buildings, are visually similar and dif- cult to distinguish. Previous research in the area tends to focus on matching raw aerial image data to a set of reference images. While these methods can achieve acceptable results in speci c conditions, they struggle with variations in lighting, seasonal changes and changing environments. This thesis presents a new multi- stage method that aims to solve this using a high-level matching framework where landmarks identi ed in an aerial image are matched to a reference database. This has led to the development of a geometric feature descriptor that encodes the topography of landmarks. The proposed system therefore matches the arrangement of features rather than the appearance, which lets it distinguish individual landmarks in large sets (20,000+ features). Since the arrangement of landmarks often is semi- structured and ambiguous, in particular when considering man-made landmarks, a matching stage has been developed that uses a number of strategies to enable matching of individual landmarks to a full database. The results have been evaluated for two conceptual vehicles with acceptable results, highlighting the strengths of the proposed system as well as areas for improve- ment.