The upshot is much better accuracy in urban canyons, and a small improvement where GPS was already good.
* Obviously people making chips and apps know this and try to mitigate it.
There are two big tricky parts about urban canyons. First, yeah, you still have quite a few satellites, but they're all in the same directions. Satellites directly above you don't really tell you anything. Satellites in front of and behind you can only tell you how far you are along that axis. You don't have any satellites to the sides, because you're in a canyon. So in an idealized version of a really bad urban canyon, the GPS can tell how far you are on the street, but not which street you're on, which is what the user actually wants to know. (I did a lot of work on knowing this from context, but it's still quite a mystery on a cold start.)
The second is that, unlike natural canyons, signals in urban canyons tend to bounce. So instead of seeing the satellite missing, you see it giving a signal that's consistent with if you were in the next street over. Which is the same problem we had in the first place. There's a lot of outlier detection done in the chips, but in a really noisy environment, sometimes that'll inevitably end up throwing out the good data and choosing the outlier.
It can be significantly reduced if the GPS has access to a 3d model of the nearby buildings - then the GPS can guess which signals are probably reflections and which are direct.
Alas, I think this isn't done outside data centers/labs, because the data download to have a large 3d model to get a GPS fix isn't a service anyone wants to run for free.
When you only way have one radio signal from a satellite, it is impossible to tell how the ionosphere has effected the signal.
When you have two, and each a slightly different frequency, you can model signal path changes and apply some corrections for better general accuracy.
Source: I watched the keynote and I’ve run both.
Return to the route.
Return to the…
FUCK YOU SHORESY, I’M ON THE ROUTE.
No, a more accurate GPS will not fix Apple's bugs.
If you could elaborate, I'd be interested. It seems very specialistic (though you drop it as if it should be obvious) so I doubt most people here know the terms.
The reason to use PPK is weight and cost - it just uses a normal GPS receiver and doesn't need an RTK sideband antenna, since the base station information can be downloaded over the internet at postprocessing time.
RTK/PPK gives ~3cm precision, while standard GPS gives 6m precision. This new dual-band giving 30cm precision means it is good enough to not use RTK/PPK except in the most demanding applications.