In perspective drawing, everything needs to be exact, (except for organic lines). When I draw perspective in my art class, we require a ruler at all times. The lines all have to be the same length or else it will be out of proportion.

There is a thing called orthographic projection which is a projection used for architects, and engineers. It talks about how all the lines have to be parallel.

https://www.britannica.com/topic/drafting/Dimensions-and-tolerances#ref213029