Figure 12.

Interpolation of the value at point P (x_p, y_p) (greydot) by a succession of polynomial interpolations. First, the values at points (y_i, x_p) (i = 1,2,3,4) (white dots) are interpolated (in the x-direction) using Eq. 2. These new values are then used as input to interpolate in the y-direction to determine the value at the point P (x_p, y_p).