Today a friend of mine made me realize that roundabouts have “perfect” road markings around them and i started wandering how a machine would go about making a circle without a compass-like system. So i tried google but every result led to either a janky home made compass or some sort of hand-drawing technique. I assume it should be possible to draw a circle knowing the radius in an analog system without a compass but i can’t figure out how. Plus i don’t know how the physical structure of a roundabout is made to be round and that is even weirder to think about.
TLDR: How are roundabouts and round road markings made?
To get a step deeper into your “how can a machine draw a circle” question. Mostly it can’t. Even with an open-loop control system dragging the ‘pen’ at a fixed angle, you would need to have defined that curve in software somewhere, where it will be a barely-noticable set of X-Y steps, not a pure curve, otherwise you cannot be sure it would return to the origin.
Luckily, you only need a few decimals of pi to approximate that far beyond what any human eye could discern.
Break any digitally defined curve down far enough and you will see those discrete steps, but with modern technology, we just never notice it.