Tobii Pro Spark - Maximum Gaze Angle; Maximum Screen Size; Operating Distance; Precision

32 / 33
Maximum gaze angle
The maximum gaze angle for which the eye tracker can perform robust
and accurate tracking on the eyes. The gaze angle is the angle ABC with
A = center of the
eye tracker (midpoint between the two eye tracking
sensors), B = eye position (midpoint between the left and the right eye)
and C = stimuli point.
Maximum screen size
The maximum screen size supported by the standard eye tracker setup
(i.e., mounting the
eye tracker directly on the screen).
Operating distance
The minimum and maximum distances between the subject’s eyes and
the surface covering the eye tracker sensors at which eye tracking can
be done while maintaining robust tracking.
Precision
Describes
the spatial angular variation between individual and
consecutive gaze samples (Root Mean Square), calculated on raw data.
Sampling frequency
The number of data samples per second output for each eye.
Expressed in Hz units, where 1 Hz = 1 sample per
second.
Total system latency
The duration from the mid
-point of the eye image exposure, to when
a sample is available via the API on the client computer. This includes
half of the image exposure time, image read
-out and transfer time,
processing time
,
and time to transfer the data sample to a client
computer.
Tracker and client time
synchronization
The eye tracker and software client clocks can drift naturally during
operation. To compensate for this, the Pro SDK will periodically ask the
eye tracker
about its current timestamp, noting the system timestamp
when the request is sent and received. This data is then used to
calculate how the system time corresponds to the device time.
Video
-based Pupil
Center Corneal
Reflection (PCCR)
eye
tracking
At the center of
this technique is a hardware setup that consists of one
or two video cameras and one or multiple sets of infrared
-light
illuminators. The cameras capture images of the eyes, and the
illuminators produce reflections on its surface. These images are
processed by algorithms that identify the pupil and the reflections
caused by the illuminators. This information is then combined with
different parameters from a 3D model of the eye and used to map the
gaze onto the stimulus.