Does GPS based Follow Me drones only work outside?

I'm really new to everything about this but I have basically got to understand that follow me drones are either tracking you with a camera or using some sort of GPS tracking system. My question is if the GPS based ones actually need to communicate with a satellite to track you or if they sort of create their own GPS network between the drone and the user wearing something that can be tracked ("ground control station" is a word I have seen mentioned a couple times?). Like it would make sense to me if that was the case? Just the drone and a wearable device communicating between each other but I wanted to ask the professionals about this since I have a hard time finding an explanation to how it actually works beyond just the word "GPS tracking". via /r/drones https://ift.tt/2qSfWvD