Telescope Aiming Point Tracking Method for Bioptic Driving Surveillance

Abstract

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.

Methods for Automated Identification of Informative Behaviors in Natural Bioptic Driving

“…An infrared camera equipped with an infrared LED illuminator and a band pass filter is used for robust head movement tracking in the real world driving conditions. The tracking technique allows detection of bioptic use and estimation of gaze through the telescope with slightly better than 1° accuracy across a wide field of view [19]. Importantly, the tracking technique requires only one-time calibration when the system is installed in a car.…”

“…In our system, the downward head movement causes a change in the angles of the reflective marker triangle image. We have developed a technique to estimate the telescope aiming point (registered on the scene image) based on the angles [19]. However, other head movements, for instance lateral head movements, can also cause the angles to change.…”

“…We have not seen any report that evaluates gaze interpretation. The accuracy of our telescope tracking technique is slightly better than 1° [19], but many objects drivers look at are smaller than 1°. For example, at 50m, a 24-inch stop sign is a little less than 0.7°, and at 200m, the width of sedan car is about 0.5°.…”

Driving with Bioptic Telescopes

“…No comprehensive investigations to date have video recorded bioptic drivers behind the wheel and then analyzed the video to determine for example, how frequently they “dip” the telescope, under what conditions, and what points in space they direct it towards. Measurement techniques have been described for video-recording bioptic drivers and for measuring telescope aiming, 48,49 which may assist in addressing these types of questions in future research. There are some who have suggested that bioptic telescopes are not primarily used by visually impaired persons for on-road driving but are principally used to pass the visual acuity screening test when applying for licensure, and then are not used once the driver is licensed and on the road without a rehabilitation specialist in the vehicle monitoring his/her behavior.…”