Yes, until the property market crashed in the US I was a land surveyor. This is the same principle used in RTK/GPS (real-time kinematic) measurement. A "zephyr"

Yes, until the property market crashed in the US I was a land surveyor. This is the same principle used in RTK/GPS (real-time kinematic) measurement. A "zephyr" GPS antenna is placed on a coordinate "base" usually 2m above it on a tripod, which then continually updates and measures the difference in distance between it and the "rover" antenna carried by the surveyor, as well as the satellite network. I used to have an updating map on the web of all the GLONASS satellites the Russian government had put into orbit, but it was taken down.