Figure 4.

The auxiliary coordinate system, used for estimating the cornea center from glints. The origin O is at the optical center (i.e., the focal point) of the utilized pinhole camera model. Here q_L is the location of i’th LED light source, ĝ_i is the corresponding glint on the corneal sphere, l̂_l is the image of the i’th glint on the image plane, and Ĉ_l is the cornea center. Each LED, and the corresponding glint, has their own coordinate system with the shared origin. The figure is adapted from Hennessey et al. (10).