Coordinate systems
In the Tobii Pro SDK you will come across a few different coordinate systems. In order to be able to correctly interpret coordinates delivered from the SDK it is important that you understand the difference between these coordinate systems.
In the description of the coordinate systems, the word user denotes the person whose eyes are being tracked by the eye tracker.
Active Display Coordinate System (ADCS)
All gaze data are mapped into a 2D coordinate system aligned with the Active Display Area. When using an eye tracker with a monitor, the Active Display Area is the display area excluding the monitor frame. For eye trackers used without a monitor, the Active Display Area is the area used to show the calibration points when doing the calibration of the eye tracker to the user’s eyes.
The origin of the Active Display Coordinate System is the upper left corner of the Active Display Area. The point (0, 0) denotes the upper left corner and (1, 1) the lower right corner of it.
User Coordinate System (UCS)
Most data, available from screen based Eye Trackers from Tobii, that describe 3D space coordinates are given in the so-called User Coordinate System or UCS for short. The UCS is a millimeter-based system with its origin at the center of the frontal surface of the eye tracker.
The coordinate axes are oriented as follows: the x-axis points horizontally towards the user’s right, the y-axis points vertically towards the user’s up and the z-axis points towards the user, perpendicular to the front surface of the eye tracker.
