2. If a polygon (or any shape) lies on a plane forming an angle $\theta$ with the horizontal plane (which also means that a vector orthogonal to the polygon forms an angle $\theta$ with a vertical vector (and $\theta$ is computed using a dot product)), then its area is equal to the area of its projection on the horizontal plane (the "top view") divided by $\cos\theta$. If $\theta$ is 45°, this gives the $\sqrt{2}$ factor.