:<math> \mathbf{\hat{k}'} = \cos\phi_w \mathbf{\hat{u}_0} + \sin\phi_w \mathbf{\hat{u}_l} +
\mathbf{(\hat{k} \cdot \hat{t}) \hat{t}}, \quad 0 \le \phi_w \le \alpha</math>
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where the resolution of the angle θ<sub>w</sub> is chosen to be the same as the resolution of the incident ray.