Eye tracking refers to monitoring the eye movements. There are a number of techniques for measuring eye movements. The most common and widely used technique is video-based eye tracking that uses video cameras to record the image of the eye and extracts the information from the eye image.
A gaze tracker is a device that measures the eye movements and additionally estimates the user’s gaze using the information obtained from the eyes. Depending on the gaze estimation technique employed, the output of the gaze trackers may be the Point-of-Regard (PoR) or Line of Sight (LoS) in 3D space, or it may be a point in a 2-dimensional image (e.g., the user’s field of view (scene image) or a computer display). Find detailed review of recent eye models and techniques for eye detection and tracking in this paper: In the Eye of the Beholder: A Survey of Models for Eyes and Gaze.
Remote vs Head-Mounted Gaze Trackers
Video-based gaze trackers can be categorized into two different types: Head mounted gaze tracker (HMGT) and Remote gaze tracker (RGT).
|Remote Gaze Tracker (RGT)||Head-Monted Gaze Tracker (HMGT)|
|Setup||The system components (camera and infrared light sources) are placed away (remote) from the user. Some of the RGTs have more than one camera to track the eyes and the face.||The eye and the front-view cameras are mounted on the head. Some of the HMGTs do not have a front-view camera and estimates the gaze in 3D space. Binocular HMGTs have two eye cameras for tracking both eyes.|
|Gaze Estimation Space||
RGT systems usually only allow for estimating the Point of Regard (PoR) on a fixed planar surface (fixation plane), e.g. a computer display.
HMGT systems are commonly used for estimating the Line of Sight (LoS) and the gaze point of the user in his field of view.
|Main Disadvantage||Limited range of movements of the subject's head and limited field of view.||Mounting on the head.|