The objective of this page is to provide a description of the different components and processes that are responsible for the timing accuracy of Tobii Eye trackers.
Tobii Eye Trackers are an advanced version of the traditional Pupil Centre Corneal Reflection (PCCR) remote eye tracking technology. Near infrared illumination is used to create reflection patterns on the cornea and pupils of the eye of a user. An image sensor then captures images of the eyes and respective reflection patterns, and sends them to the eye tracker firmware ‐ TET Server (or Tobii Eye Tracking server). The position of the eye and the point of gaze are then derived with high accuracy from image processing algorithms and a mathematical model of the eye. The TET Server also time stamps each image when it arrives to the server using a time function dll – TTime.dll. This function extracts timing information from a high resolution counter located on the computer or eye tracker processor. The TET Server then recalculates this timestamp in order to show the time when the image was captured by the sensor.
In the ‐50 Series, X2-60 and X3 eye trackers the TET Server is installed and run from an external computer that communicates
In the T/X Series and X2-30 eye trackers the TET Server runs on a computer integrated in the eye tracker hardware. As a result the images from the sensor are processed in the eye tracker and the resulting gaze data is then sent to the network via a TCP/IP Lan or USB connection. This setup allows a simpler and more efficient
The latency of an eye tracker corresponds to the interval measured from the time when an image is captured by the sensor (mid exposure) to when gaze data is outputted by the the TET Server to the network or to an eye tracking application (e.g. Tobii Pro Studio). This delay is the sum of the time taken for camera exposure,
There are two types of latencies reported in the Tobii eye tracker specifications: "processing latency" and "total system latency". The total system latency is defined as the duration from mid-point of the eye image exposure, to when a sample is available via the API on the
Processing latency describes the time required by the eye tracker processor to perform image processing and eye gaze computations. This time should not exceed the sampling interval time of the eye tracker.
The position of the eye is estimated based on an image taken by the sensor. The sensor is set to a fixed exposure time and the timestamp for each gaze data is set to indicate the middle of exposure time. This mid