**2.3. Daugman's gross alignment model**

Daugman's gross alignment model maps each point within the iris to the polar coordinates (*r*, *θ*) where *r* is from the interval 〈0, 1〉 and *θ* is the angle from the interval 〈0, 2*n*〉.

The model compensates the pupil enlargement and dilatation due to the representation in the polar coordinate system, invariant to size and translation. However, the model does not compensate for rotational inconsistency, which is solved by shifting the iris template in the direction of the *θ* at the comparison stage until both templates reach a match. The introduction of the coordinate system is shown in **Figure 6**.
