Originally Posted by
Skipjacks
GPS is accurate to within 3 feet or less, even on a phone, if the phone's decent enough. On my LG G5 my GPS can tell which side of my living room I'm in, from inside the house, with the GPS signal going right through the roof. I can bring up my location on Google Maps and look at the satellite feed and I can watch my phone move around my house. My bike phone that I use for mileage and what not is an off brand cheaper Android and it's not nearly as good. It's fine when I'm outside but it can't get a lock on GPS without a direct line of sight (tree branches and stuff not withstanding)
This three feet claim is way better than what you could get with GPS last time I was working on it. Half a dozen years ago GPS could only give you +/- 30 feet. If you've got some references to that kind of improvement, I'd like to see them.
Are you sure (a) your phone isn't doing some sort of differential GPS, perhaps with multiple nearby cell towers? Do most cell phones now also use GLONASS, and is that sufficient to improve the accuracy ten-fold?