RTK positioning

Ordinary GPS, like the one in your phone, is usually off by several feet. That is fine for driving directions but useless for mowing up to a flowerbed.

RTK fixes this with a second receiver that stays in one known spot, called the base station. Because it never moves, it can tell how far off the satellite signals are at any moment. It sends that correction to the moving machine by radio or over the internet.

With a clear view of the sky, RTK gets down to about one to two centimeters. Trees, buildings and narrow passages can block the satellites and make it lose that precision.