What is Parallax Correction? How does this affect my eye tracking performance?

Parallax affects the perceived accuracy of the eye tracking dot drawn on the video from the front facing camera.

Depending on the use case, AdHawk deals with this parallax in one of two ways. Automatic parallax correction and gaze depth options located in Settings > Eye Tracking. The best eye tracking performance will be achieved when these two features are used appropriately.

WHAT IS PARALLAX CORRECTION?

Parallax correction corrects for parallax error which manifests as a gaze offset due to the distance between the camera location on the glasses (on right side) compared to the gaze origin center (cyclopean scanner).

Below are some visual examples of a parallax error. The green dot is using automatic parallax correction where the red dot is when the system is using a fixed gaze depth for projecting the red dot on a certain plane. The line is all of the possible positions which the dot can be drawn depending on the depth of the gaze.

In the example below, the user is always looking at the green dot (automatic parallax correction) and the red dot is the projection of the dot on a plane of about 60cm from the user. The red dot appears to be “off” when the set depth and depth at which the user is looking does not match.

‘Automatic parallax correction’ uses vergence measurement in order to correct for the parallax error which means both eyes must be visible and free of noise in order for automatic parallax correction to operate correctly.

WHEN DO I TURN ON/OFF THE AUTOMATIC PARALLAX CORRECTION?

Turn on ‘Automatic parallax correction’ if:
You do not know your depth plane or will be looking at more than one depth plane. For example, recording an eye tracking session where the user is looking at various objects placed at various distances away. Turning on the ‘Automatic parallax correction’ should improve the accuracy of the gaze dot on the camera feed.

Turn off ‘Automatic parallax correction’ if:
You are doing an eye tracking session with a known depth plane AND adjust the ‘Gaze Depth’ in settings to the depth at which the targets are displayed. For example, recording an eye tracking session of a user reading, turn off ‘Automatic parallax correction’ and adjust ‘Gaze Depth’ accordingly.