ABSTRACT
12.1 Principle of Operation
In the context of HCI applications, Eye Gaze Tracking (EGT) systems are primarily used to determine, in real time, the point-of-gaze (POG) of the subject's eye on the computer screen. The Point-Of-Gaze (POG) is commonly derived through geometric considerations driven by knowledge of the direction of the optical axis of the eye (OAE), i.e., the 3-dimensional vector indicating the direction in which the user is aiming his/her gaze. The determination of the OAE is estimated from real-time analysis of the image of the eye captured by an infrared video camera. The analysis is based on the location of two critical landmarks in the image: the center of the pupil and the center of the reflection of infrared light on the cornea of the eye (also known as the "glint"). The relative position of these two landmarks, with respect to each other, within the image of the eye captured by the infrared camera is a function of the OAE and, combined with geometrical knowledge obtained in a calibration session, prior to EGT use, can reveal the POG of the subject. Figure 12.1 illustrates the process for POG determination as a block diagram.
