Could the Asymmetric Aperture method be an adequate interim solution to the vertical shift from z-axis movment as the head moves forwards and backwards?
Patent “Explicit raytracing for gimbal-based gazepoint trackers” (WO 2006108017 A2) seems to have expired, and is now in the public domain.
http://www.google.com/patents/WO2006108017A2?cl=en
Interactive minds eye tracking uses the Asymmetric Aperture method:
To achieve high gaze point tracking accuracy, the image processing algorithms in our eye tracking systems explicitly accommodate several common sources of gaze point tracking error.
The accuracy of video eye trackers is typically sensitive to head motion along the camera axis.
As the head moves toward the camera the predicted gaze point (if uncorrected for range) moves radially away from the camera, and as the head moves backward, the predicted gaze point moves radially in toward the camera.
Typically, when a person is about 60 cm from the camera, and looking at a point toward the top of the computer screen head motions of 2.5 cm along the camera Z axis result in predicted gaze point variations of about 1,9 cm.
All our eye trackers use the patented Asymmetric Aperture Method to measure variations in the range between the camera and the cornea of the eye, and they use the range information to minimize gaze point tracking errors resulting from longitudinal head motions.
http://www.interactive-minds.com/eye-tracker
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Explicit raytracing for gimbal-based gazepoint trackers WO 2006108017 A2
Abstract
One embodiment of the present invention is a method for computing a first gaze axis of an eye in a first coordinate system.
A camera is focused on the eye and moved to maintain the focus on the eye as the eye moves in the first coordinate system
A first location of the camera in the first coordinate system is measured
A second location of the eye and a gaze direction of the eye within a second coordinate system are measured
A second gaze axis within the second coordinate system is computed from the second location and the gaze direction
The first gaze axis is computed from the second gaze axis and the first location using a first coordinate transformation.
The patent is expired?:
May 14, 2008 32PN Ep: public notification in the ep bulletin as address of the adressee cannot be established
Free format text: NOTING OF LOSS OF RIGHTS PURSUANT TO RULE 112(1) EPC - FORM 1205A (05.03.2008)
http://www.google.com/patents/WO2006108017A2?cl=en
TLDR: This method seems an awful lot more complex than it is.
But basically it’s projecting an IR pattern onto the eye that changes as the range changes.
So you can measure range by looking at how the pattern looks.
Pretty simple, doesn't require a ton of math to compute, and gives you a highly precise range measurement.
