Very interesting but not practical in a lot of situations rad1 is not equal to rad2, so the solution is in a double reverse curve function, the maths is very simple. I have looked at this for years and after looking at the video has given me some ideas.
The variables are, Total length, Rad1, Rad2, Offset dist. so you can solve for a missing item.
Rad1, rad2, offset, length is missing.
Rad, length, offset, rad2 is missing
Non parallel much more complex.