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Fig. 5. External photogrammetric measurement of the wing kinematics of a
free-flying steppe eagle Aquila nipalensis coming in to perch on its
handler's arm. Left panel shows one of a stereo pair of images taken at 500
frames s–1. Right panel shows a calibrated reconstruction of
the lower surface of the left wing based on stereo-matching of natural
features of the plumage. Black points on the wing denote measurements,
connected by straight lines to assist in visualizing the wing topography; the
colour map denotes the local geometric angle of attack of the interpolated
wing surface with respect to the horizontal. The isolated black points denote
reference measurements on the head and tail, indicating the longitudinal axis
of the bird. Note that whereas the angle of attack and camber of the proximal
section of the wing is relatively consistent in a spanwise direction, the
distal portion of the wing is set at a much greater angle of attack. This
reflects the angle of attack of the interpolated surface and does not take
account of the local twist of the primary feathers, which will be measured in
future work. An animation of this perching sequence is available (Movie 1 in
the supplementary material).
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