A bioptic telescope is a visual aid used by people with impaired vision when driving in many US states, though bioptic driving remains controversial. Objective data on how and when bioptic drivers use the telescope and what they look at with it are crucial to understanding the bioptic telescope's effect on driving. A video-based technique to track the telescope's aiming point is presented in this paper. With three infrared retro-reflective markers pasted on the bioptic spectacles' frame, its movement is recorded using an infrared camera unit with infrared LED illuminators. The angles formed by the three markers are used to calculate the telescope's aiming points, which are registered with road scene images recorded by another camera. The calculation is based on a novel one-time calibration method, in which the light spot from a head-mounted laser pointer projected on a wall while the head is scanning is recorded by the scene camera, in synchronization with the infrared camera. Interpolation is performed within small local regions where no samples were taken. Thus, non-linear interpolation error can be minimized, even for wide-range tracking. Experiments demonstrated that the average error over a 70°×48° field was only 0.86°, with lateral head movement allowed.
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