Given three polyhedra $P$, $Q$, and $R$ in dimensions $a$, $b$, and $c$ respectively, with $a\leq b\leq c$, with the additional condition that: $P=\pi_1(Q)=\pi_2(R)$, where $\pi_1$ and $\pi_2$ are projection maps. Then
Main Question: When is it true that there is a projection map $\pi$ with $Q=\pi(R)$?
(1) What if we consider only (bounded) polytopes?
(2) What if we further restrict to just convex cases?