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One of the principal difficulties of video inspection of overhead power distribution lines from a helicopter is the blurring of the image due to rotation of the camera in its gimbals and the translational motion of the helicopter. The author presents a kinematic model describing the sightline geometry which includes the effect of the helicopter's rectilinear motion in three degrees of freedom. It is shown that, except for locations very near to the object being inspected, the velocity flow field of the image is substantially uniform. The image Jacobian is used to predict how much blur is to be expected along a typical flight path during inspection operations. An important conclusion is that this will be greater than the tolerable limit of 1–2% unless the camera is rotated at a rate which compensates for the helicopter's rectilinear motion – the implications for the design of an automated object tracking system are discussed. The maximum singular value of the image Jacobian is proposed as a quality measure for inspection from various locations of the helicopter relative to the target object. It is found to be an useful figure of relative merit but too conservative to provide a realistic upper bound on image blur.
Dewi Jones (Sat,) studied this question.