Solving Parallax Error for 3D Eye Tracking

Head-mounted eye-trackers allow for unrestricted behavior in the natural environment, but have calibration issues that compromise accuracy and usability. A well-known problem arises from the fact that gaze measurements suffer from parallax error due to the offset between the scene camera origin and eye position. To compensate for this error two pieces of data are required: the pose of the scene camera in head coordinates, and the three-dimensional coordinates of the fixation point in head coordinates. We implemented a method that allows for effective and accurate eye-tracking in the three-dimensional environment. Our approach consists of a calibration procedure that allows to contextually calibrate the eye-tracker and compute the eyes pose in the reference frame of the scene camera, and a custom stereoscopic scene camera that provides the three-dimensional coordinates of the fixation point. The resulting gaze data are free from parallax error, allowing accurate and effective use of the eye-tracker in the natural environment.