It is generally believed that far PD (pupillary distancePupillary distance:
The distance between the center of the pupils. Also known as PD. when someone focusing on a far object) is constant. Some believe that PD should be measured with sub-millimeter accuracy. In the following experiment, we show a simple method to measure natural pose lookout points. Clearly, the distance of the left and right lookout point gives the PD. For the measurement, one only needs a camera with high optical zoom and an eyewear with some kind of a grid on the lens. The testee is than asked to stand about 2-3 meters from the camera, face to the camera and look into its objective. When the testee is in the right pose a photo is taken.
Note that at this time point wherever the center of the pupil lies on the grid of the lens is exactly the experimental lookout point of the frame, since the testee’s gaze-vector coincides with a pixel-ray of the camera. Hence with this method the accurate lookout point of a customer in a surely far gazing position can be determined.
If this experiment is repeated several times on a subject, with some head pose motion between the photo shots, then a distribution of the left and right lookout points will become visible. In our experiment, we have used an image editing software to mark the position of the different lookout points.
As you can see in the pictures below, the results of the test were less than optimal. The measured Pupillary distances of a given testee were several, in some cases 4-5, millimeters apart.
We also experienced that in many cases one side of the lookout point has a much higher diversity than the other. We believe that this effect is due to the fact that the leading eye has a more constant position, while the other is moving more around.