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A Cooperative Approach for Autonomous Landing of UAVs
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This dissertation presents a cooperative approach for the autonomous landing of MRVTOL
UAVs (Multi Rotor-Vertical Take-off and Landing Unmanned Aerial Vehicles). Most
standard UAV autonomous landing systems take an approach, where the UAV detects
a pre-set pattern on the landing zone, establishes relative positions and uses them to
perform the landing. These methods present some drawbacks such as all of the processing
being performed by the UAV itself, requiring high computational power from it. An
additional problem arises from the fact most of these methods are only reliable when the
UAV is already at relatively low altitudes since the pattern’s features have to be clearly
visible from the UAV’s camera. The method presented throughout this dissertation relies
on an RGB camera, placed in the landing zone pointing upwards towards the sky. Due to
the fact, the sky is a fairly stagnant and uniform environment the unique motion patterns
the UAV displays can be singled out and analysed using Background Subtraction and
Optical Flow techniques. A terrestrial or surface robotic system can then analyse the
images in real-time and relay commands to the UAV.
The result is a model-free method, i.e independent of the UAV’s morphological aspect
or pre-determined patterns, capable of aiding the UAV during the landing manoeuvre.
The approach is reliable enough to be used as a stand-alone method, or be used along
traditional methods achieving a more robust system. Experimental results obtained from
a dataset encompassing 23 diverse videos showed the ability of the computer vision
algorithm to perform the detection of the UAV in 93,44% of the 44557 evaluated frames
with a tracking error of 6.6%. A high-level control system that employs the concept of
an approach zone to the helipad was also developed. Within the zone every possible
three-dimensional position corresponds to a velocity command for the UAV, with a given
orientation and magnitude. The control system was tested in a simulated environment
and it proved to be effective in performing the landing of the UAV within 13 cm from the
goal.
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Palavras-chave
UAV landing systems Robotic cooperation Background Subtraction Optical Flow motion patterns high-level control