# Projection of the area of a bounded plane over other bounded plane

I have two bounded planes $\pi$ and $\rho$ in three dimensional space. Each plane is bounded by a coplanar rectangle. How can I find the orthogonal projection area of $\pi$ over $\rho$?

I'm not sure what you mean, but one can easily find the dihedral angle $\phi$ between two planes: $\cos\,\phi=\frac{a^\prime a+b^\prime b+c^\prime c}{\sqrt{a^2+b^2+c^2}\sqrt{{a^\prime}^2+{b^\prime}^2+{c^\prime}^2}}$, and then use Rodrigues's rotation matrix, using the line formed by the two planes as the axis. – J. M. Sep 12 '11 at 16:53