Not to mention wireless networks like the ones for the airtag or the wifi endpoints mapping google has could be adapted to share positions of "right here, right now" anonymously.
Which means that if only one device knows where it is, you can calibrate, and if several know, you can even correct for mistakes.
If the system is precise enough, you only need to calibrate once in a while. Being at home/office, on the local wifi, once, could be enough.
Besides, nobody wants the GPS to go, but it's a nice alternative that can't be jammed by enemy forces and can be used for hiking, diving, etc.
I mean the exact position, down to a millimeter, when e.g. a photo sensor on a train passes past a LED mounted below the station platform. The LED's light is modulated so there can be no mistake, and its location is precisely known.
A meter precision is fine for what most people use GPS for. If the device is as precise as they say, you won't add much imprecision to the original calibration, so you will be in the right tunnel at the right time.
Which means that if only one device knows where it is, you can calibrate, and if several know, you can even correct for mistakes.
If the system is precise enough, you only need to calibrate once in a while. Being at home/office, on the local wifi, once, could be enough.
Besides, nobody wants the GPS to go, but it's a nice alternative that can't be jammed by enemy forces and can be used for hiking, diving, etc.