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?
You’re asking about something called surveying, if you want a term to search for. Modern surveying equipment uses lasers to measure the land, then they do a bunch of trig to create an accurate map. Once you have an accurate map that’s keyed to known reference points, you can design the roundabout. When you’re ready to build it, it’s just following the map and using the reference points to measure it back out.