Tobii X2-30, Руководство пользователя

Страница: 25 / 42

6 Positioning
The distance from the participant ’ s eyes to the eye tracker should be approximately 60 – 65 cm (23 – 26 ʺ ) for best performance.
However, the eye tracker can still track eye movements as long as the participant stays within the distance interval from the eye
tracker mentioned below. If the eye tracker is too close or too far away from the participant there is a risk of losing some of the
gaze data.
When the Tobii X2 Eye Tracker is used in a setup where it is not attached to a screen, it should be placed below the monitor (or
below the surface that is to be used for presenting the stimuli) without covering the bottom of the display area for the participant
watching the stimuli.
For optimal tracking, the eye tracker should be placed so that the gaze angle ( α ) illustrated below will not exceed the 36° for Tobii
X2 Compact Edition when the participant is located ~65 cm (26 ’’ ) from the eye tracker.
It is very important to have the correct distance to the monitor or the tracked object. Otherwise the eye tracker cannot track the
entire area. If the monitor or object is placed too close to the participant there is a risk that the gaze data for the corners of the
display area of the monitor will not be collected.
The correct distance can be calculated by using basic trigonometry (see image below). By assuming that the tracked area is a
half circle and that the diagonal from the center of the screen or other stimuli to its top corner constitutes the radius of that half
circle, it is possible to calculate the distance needed between the participant and the stimuli using the following formula:
Tobii X2-30 Eye TrackerUser ’ s manual v.1.0.3 - en-US
6 Positioning
19