There is no API on the Tobii eye trackers for a custom calibration procedure like the one you describe. The Tobii calibration procedure is proprietary, so I cannot give you any details, but it uses a number of parameters to build up a whole model of the user’s eyes. This makes it possible to calculate a calibration that gives good gaze tracking also for a head and eyes that moves around in 3D space in front of the eye tracker. This advanced calibration and eye model creation procedure is built into the Tobii eye trackers. The Tobii EyeX SDK does not support any kind of custom calibration, the Tobii Gaze SDK comes with an API where you can customize the calibration somewhat, but that is limited to the positions and numbers of calibration points.