Ah! I get your point, rhetorically, but should any of us find ourselves in any kind of bind where you need to figure out the radius of the body we find ourselves on, 100 meters is probably going to be a bit… short for anything that’s bigger than a very modest asteroid. Local terrain variations and measurement imprecision would dominate.
You’ll want a good number of kilometers, like a few hundred, even though you have to make observations on the same day, so it helps if your civilisation has also figured out things like calendars, couriers, letters, and scientifically-minded friends.