c# Cubic Interpolation

The method you can use for interpolating and bi cubic interpolation is described below (the noob way obviously):

        static double Interpolate(double z, double[] height)
        {
                return height[1] + 0.5 * z * (height[2] - height[0] + z
                * (2.0 * height[0] - 5.0 * height[1] + 4.0 * height[2] - height[3] + z
                * (3.0 * (height[1] - height[2]) + height[3] - height[0])));
        }