Eye tracker timing performance

Eye tracking technique Hardware Software

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.

Eye tracker latency

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,

transfer, calculation and delays in the system (eye tracker processor, network and the data recording computer). 

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

client computer. This includes half of the image exposure time plus image read-out and transfer time, processing time and time to transfer the data sample to a client computer. 

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.

Gaze data timestamp

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

exposure time is the best theoretical estimation of when the image was taken. The TET Server calculates the timestamp of each gaze point by taking the time of image arrival at the server (in Server Time) and subtracting it to a known
latency value that translates the time it takes for the sensor to capture the image (mid exposure value) and send it to the server. This latency is calculated according to the specifications of the sensor supplier (latency of image delivery algorithm).  

Download and read the following whitepaper to learn more about the timing accuracy of Tobii Eye Trackers

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