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. 2016 Mar 29;11(3):e0152307. doi: 10.1371/journal.pone.0152307

Fig 4. Calculation of the length of the radius of rotation of the center of the pupil and the radius of rotation of an iris freckle.

Fig 4

(A) Calculation of the length of the radius of rotation of the pupil center, R. Eqs 1–3 apply when the eye rotates θ from the eye position during frontal vision in the plane P, which includes the center of eye rotation and the diameter that corresponds to the minor axis of the pupil ellipse of the image plane (gray line, left figure), where r is the length between o and the center of the pupil ellipse p. (B) Next, we calculate the length of the radius of rotation of an iris freckle. When an iris freckle is on the same plane as the pupil edge, the radius of rotation, R’, is calculated by Eq 4, in which a is the distance between the center of the pupil ellipse and the center of gravity of an iris freckle in the image, b is the distance between the center of the pupil ellipse and point c in the image, point c is the point of intersection of the edge of the pupil ellipse and the line connecting of the center of the pupil ellipse and the center of gravity of an iris freckle in the image.