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?
Firstly, roundabouts aren’t perfectly round.
The city I live in is relatively small but has dozens of roundabouts. They might look round as you drive through them, but if you look from a satellite image most are just “mostly” round, and some that seem round on the ground are plain oblong.
With that in mind, you’re dealing with curves, not a perfect circle.
Different points are defined with a range of methods like survey, measuring, and just plain eyeballing.