Bilinear Interpolation (BI) Algorithm

Four gain values are determined in the horizontal and vertical patterns depending on the two angles $\vartheta$ and $\phi$ .

The gain values are weighted with their angle distances:

$$G(\phi ,\vartheta )=\frac{\left|\phi \right|\cdot G_v(2\pi -\vartheta )+(\pi -\left|\phi \right|)\cdot G_V(\vartheta )+\vartheta \cdot G_H(\phi )+(\frac{\pi }{2}-\vartheta )\cdot G_V(0)}{\left|\phi \right|+(\pi -\left|\phi \right|)+\vartheta +(\frac{\pi }{2}-\vartheta )}$$