Redo how offset vector $\vec{f}$ is calculated

[ifndefJOSH]

Previously there was an error in how the offset vector $\vec{f}$ was calculated. It would find vector $\vec{v}$ as the shortest distance from $S_n$ to $S_s$, and then project onto $S_0$. Problem was that this would often yield $\vec{0}$ as since $S_n \in S_0$ the shortest distance to $S_s$ was perpendicular to $S_n$ and thus $S_0$. This PR computes $S_s \cap S_0$ first and then computes the distance from $S_n$ to that intersection.