proportions of a perspective-deformed rectangle

Question

Given a 2d picture of a rectangle distorted by perspective:

I know tha

Answer 1

You can determine width / height by this answer Calculating rectangle 3D coordinate with coordinate its shadow?. Assume that your rectangle rotate on intersection diagonal point calculate it width and height. But when you change distance between the assumption shadow plane to the real shadow plane proportional of rectangle is the same with calculated width / height!