[PrismCrystal]

The vast majority of Google Maps users are capable of using A-GPS data, they are not reliant on a clear GPS satellite signal alone. And Google’s A-GPS data for Manhattan is extremely detailed. Again, this makes sense for a one-size-fits-all product like Google Maps.

[astrange]

That's not good enough, AGPS doesn't work near skyscrapers. The issue isn't that the signal isn't "clear", it's that it reflects off the buildings and the GPS receiver will get a clear but wrong signal.

To correct this you need something like QZSS or accurate models of the buildings to compensate for it.

[PrismCrystal]

The term "A-GPS" in common practice includes also wifi and, as I mentioned, Google's data for this is very detailed in Manhattan, too.

[astrange]

Yeah, it doesn't work for this. I've tried it in the last few months and talked to people working on location about it out of curiosity. Not in NYC specifically but in other cities.

Even short buildings have issues here - if you walk down a wide street in Tokyo, which are pretty common and often surrounded by 3-4 story buildings, with the map open and look at it closely, you will often show up on the other side of the street. (Which surprised me, because it's literally why QZSS exists.)

Afaik, the issues with WiFi are that if you're traveling at any speed there isn't much time to do scans, and the position of the WiFi networks themselves isn't clear enough because of multipath (reflections), because it is crowdsourced from other devices that don't have real ground truth locations, and because the other devices gathering info are at different heights above ground or are indoors.

The main advantage of A-GPS with WiFi is that it starts up faster and that it mostly works indoors or when you can't see any satellites.

[mycall]

The correction which Apple and Google are taking is anonymous UWB location in a mesh network via Time of Flight (ToF), Angle of Arrival (AoA) and Device-to-Device communication.

[astrange]

That is how locations are transmitted for Find My Phone/Device, and how relative close-by positioning works for AirTags and similar, but it's not used to determine absolute locations as far as I know. It would certainly be cool if it did that though.

You might be thinking of https://en.wikipedia.org/wiki/Differential_GPS.

[mycall]

3GPP Release 16 started the UWB location and position scope while Release 17 finalized the 5GC capability. Perhaps more work is being done there, I haven't been tracking it closely lately.

https://www.3gpp.org/technologies/location-and-positioning

[astrange]

Huh, is that for mesh UWB networks? I would've assumed it was for mmWave cell stations, which I've never once seen in real life.