I was going through some history of technology for a tabletop game I run, and still thinking about iberia.
I would like a method for determining latitude and longitude, aka in game coords, by making legit measurements of the world.
IRL Latitude is frankly easy with a bit of geometry and astronomy, and Longitude is bloody hard requiring two clocks one of which is solar time, and the other of which is absolute relative to a point.

Nice, I've got some ideas around this. For me, I'd like for whatever coordinates the user discovers to be relative, i.e. players can determine for themselves what location they want to consider the "center" of their world. It might also be interesting if it were fuzzy at large distances, so there isn't exact accuracy the further you are from your chosen origin. At one point I thought of using beacons as origin points, that you could link to some sort of measurement tool / compass.

maybe world spawn is a "fuzzy" origin, but beacons you've mapped can be hard relative points being later game?

I was just about to post this as a request, but saw this so I'll just comment on here.
I've been playing a modpack I built myself with a few friends, and one of the mods (Random Things) has a position filter you can create semi early that shows your coords. Currently it feels too easy to find each other using that item, but if coords were set to 0,0 everytime you respawn I think that might balance things out.
Although I'm unsure how you could use these relative coordinates with other mods unless there's a way to replace the regular coords to trick the other mods with.