Browsing by Author "Blom, Josua"

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    Accurate localisation of a multi-rotor using monocular vision
    (Stellenbosch : Stellenbosch University, 2018-03) Blom, Josua; Wiid, P. G.; Van Daalen, C. E.; Stellenbosch University. Faculty of Engineering. Dept. of Electrical and Electronic Engineering.
    ENGLISH ABSTRACT: The mid-frequency aperture array (MFAA) is planned for phase two of the square kilometre array project, which has its design phase scheduled for 2018. The MFAA's antenna arrays need to be characterised in their real world environment. The antenna array characterisation can be done with a test source mounted on a multi-rotor which is own over the antennas. However, the test source needs to be localised accurately relative to the antenna array, which is currently achieved by expensive and cumbersome methods. Accurate vision-based localisation is one possible inexpensive solution, provided arti cial reference points can be placed in the environment. Many vision-based localisation methods exist; however, the focus is often on simultaneous localisation and mapping as opposed to localisation only. The problem is simpli ed signi cantly when arti cial reference points, referred to as landmarks, are manually placed in the environment wherein the multi-rotor needs to be localised. The focus of the research presented in this thesis is therefore on accurate localisation of a multi-rotor aircraft specifically through monocular vision using manually placed artificial landmarks. The multi-rotor's state propagation was described according to a kinematic motion model. Additionally, a measurement model was designed which relates camera image measurements to the system's states. A localisation algorithm using the unscented Kalman filter (UKF) was designed and integrated. The UKF uses the sensor data from the multi-rotor as well as measurements derived from image processing to best estimate the pose of the multi-rotor. The localisation algorithm was first tested and refined in simulation, after which experimental flight tests were performed and the resulting data sets were analysed. The experimental results are promising; the algorithm localised the multi-rotor with a mean accuracy of around six centimetres relative to a differential GPS (DGPS) that was used as a baseline. A high quality DGPS can localise at an accuracy of up to two centimetres; however, the Piksi DGPS used in this project proved to be intermittently accurate and unreliable. The current accuracy of the localisation algorithm would be suitable for other radio telescope antenna arrays which operate at lower frequencies than the MFAA. However, with some improvements in hardware integration, it should be possible to achieve better accuracy than differential GPS systems at a fraction of the cost, making it a promising solution for localisation in antenna characterisation application on the MFAA.