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Remote Eye-Gaze Tracker (REGT) is a
device for a remote (i.e., non-contact) estimation of the Point-of-Gaze (PoG). Simply put, an REGT system can tell what you are
looking at. The vast majority of remote eye-trackers are video-based; the
advanced REGTs also allow free head movements. The unique feature of the REGT
system described below, is that it is calibration-free for the user, i.e.,
unlike in other eye-trackers, there is no explicit calibration procedure that
user is required to actively participate in.
Basic Physiology
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Let’s start with the definition of the
Point-of-Gaze.
The figure on the right shows a sketch of a
cross-section of the eye. A light enters the eye through the cornea, pupil and
crystalline lens and an image is formed on the retina (a layer with
photoreceptors). Fovea is a region on the retina with the highest density
of photoreceptors (cones). Therefore, for an object to be seen in most
details – it should be projected onto the fovea.
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Cross-Section of the Eye
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The eye-ball can be modeled as a sphere with the
center d. The cornea can be
modeled as a spherical section with the center of curvature c. A line connecting d, c and the center of the pupil, p, is called the optical
axis of the eye. The optical axis, ω,
is in fact, an axis of symmetry of the eye. However, the gaze is aligned
with the visual axis, ν, which connects the fovea and
the center of curvature of the cornea. An intersection of the visual axis
with the scene (e.g., computer monitor) defines the Point-of-Gaze (PoG).
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Eye-ball Model
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next…
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