Does anyone here have any insights or opinions on L5 only navigation? oneNav seems to think it's better than L1+L5, citing lower complexity and power usage, but with maintained accuracy. Sounds too good to be true, will devices skip the L1 band eventually?
iPhone 14 Pro comes with dual-frequency GPS
91–100 of 205 posts
Re: iPhone 14 Pro comes with dual-frequency GPS
#92Earlier quoted context omitted.
> GPS was never designed to be mm level accurate Kind of. Consumer/public GPS was never to be that accurate. Galileo for example, has the following accuracy: 1 metre (public), 1 cm (encrypted) I'm sure the same applies to other systems too.
I don't really see the strategic importance of 1 meter Vs 1 cm positioning... Is the enemy missile going to miss the bunker because it hit 1 meter off? Or the enemy built their airport 1 meter wonky because they didn't have access to 1 cm level accuracy?
Military stuff can be moving, sometimes quickly, so more accuracy at one point in the trajectory could result in more accuracy later on
Re: iPhone 14 Pro comes with dual-frequency GPS
#93Earlier quoted context omitted.
It does have it’s own GPS. But if it tethered with your phone, it uses that instead to save battery life. The same is true for cellular Apple Watches.
Similarly, if you are using CarPlay, it will use your car's GPS instead of the built-in one. I figured this out when my car's GPS developed a fault which often gave a lock hundreds of meters away from my actual position, and my phone did the same thing when connected via CarPlay.
Cars also do dead reckoning with wheel and steering data so you get pretty decent data in tunnels where basic GPS fails.
Re: iPhone 14 Pro comes with dual-frequency GPS
#94Earlier quoted context omitted.
I live in San Francisco. We don't exactly have the tallest buildings, but I can assure you from years of tracking runs in the downtown area here and nearby forested areas, GPS gets very screwed up unless it has a clear view of the sky. This is with a variety of Garmins, Apple iPhones and Apple Watch. I'm looking forward to the newer devices with L5.
It's known as the 'urban canyon' effect. 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.
Uber showed this in 2018, I don't know how widely used it is now. I doubt any phone app uses it offline at least.
Re: iPhone 14 Pro comes with dual-frequency GPS
#95Earlier quoted context omitted.
Yeah. I used various Garmin GPS devices before, GPS (eTrex 30, gpsmap 62s) and GPS+GLONASS+Galileo. But my multi-band gpsmap 66sr gets a fix insanely quick compared to these other devices and the tracks are very accurate/steady. Here is a nice review that compares the gpsmap 66sr, gps 66i, iPhone 12 Pro and Fenix 6x Pro Solar: https://hikingguy.com/hiking-gear/garmin-gpsmap-66sr-review-...
I've been thinking about getting one of those, I would really want to buy a GPSMap 66sr but I also use InReach a lot. Which the 66i has, but it lacks the dual-band GPS... So neither option is really perfect. And it's a big expense for me so I don't want to buy something that gets superseded a month later (again) In the end I decided I'd wait until Garmin comes up with a GPSMap which has both dualband and InReach. But…
Luckily I don't need InReach, so it was an easy decision for me. Last year I made the mistake to cheap out and get a 64sx. It's a fine GPS, but it's was not really a big improvement over my 62s. Having GLONASS and Galileo as well was nice, but the 64sx is not multi-band, only has a few extra connectivity options, and still has the same old interface as the 62s.
However, I love the 66sr. Not only is it fast and accurate, the screen is so much nicer than the 62/64 series. The UI has the same base interface, but looks much refreshed compared to the 62/64. And I love the support for Live Geocaching. No need to plan ahead and do pocket queries, but I can just download caches on-device.
I was first a bit hesitant about the built-in lithium battery (no more replaceable AA batteries), but then the 66sr has more than double the battery life of the 66s (36 hours vs. 16 hours), so it's not an issue in practice for my uses.
Re: iPhone 14 Pro comes with dual-frequency GPS
#96Earlier quoted context omitted.
I for one absolutely recall "classic" GNSS based purely on GPS. The combination of only having GPS, early slow hardware with only cold starts, young software implementations, made for quite a ropey experience. I think my first proper experience was a PCMCIA GPS card in an HP IPaq running TomTom 2, or possibly some Garmin version. Revolutionary at the time, and brilliant on long journeys, but compared to today it was…
I still have an old Garmin for sea kayaking that I sometimes use. With a completely clear view of the sky it can easily take quite a few minutes to get a fix.
I've got an eMap - last time I tried it (after it was off for N years), it took upwards of 20 minutes to get a fix with a clear sky because it could only track (AFAIK) 6 satellites and without the hints from recent use, it struggled badly.
Re: iPhone 14 Pro comes with dual-frequency GPS
#97Earlier quoted context omitted.
Are there any phones that average readings from GPS, GLONASS, and GALILEO together for better accuracy?
Most phones since 2013 or so for GLONASS, and most after 2017 or so for GALILEO, at least in the US. These constellations needed US approval to be allowed as supplemental data, and it still requires an initial lock to GPS before feeding them in. GLONASS is only one of the constellations not broadcasting a civilian second band. Additionally, Beidou is still banned and blocked in firmware while in US even though the sa…
> it still requires an initial lock to GPS before feeding them in
Is there any technical reason, or is it just protectionism? (as in, no GPS lock? No lock at all, even if Galileo and Glonass are 100% fine!)
> Beidou is still banned and blocked in firmware while in US even though the satellites are broadcasting, since this constellation lacks US approval
Is it legal to use a Xiaomi phone in Wifi only mode with Beidou GNSS?
> Here's some slides about BeiDou's technical details, specifically note the 2-way messaging
Super interesting, ty! I see interesting details like "Horizontally positioning accuracy is about 1.5m" so it should be better than GPS! Also, it supports 300k SMS/h with a coverage over Japan, India and Thailand!
I would love to play with Beidou!
Re: iPhone 14 Pro comes with dual-frequency GPS
#98Xiaomi released a phone with dual frequency GNSS in 2018 (with the Broadcom BCM4775 chipset), and as far as I know most Android phones have had it since then, or maybe a bit later. If you want to see if your phone supports it, try GPSTest. Garmin has recently released several watches with it as well, both their high end models and some more affordable ones. They also have an auto mode that switches it on or off depen…
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Re: iPhone 14 Pro comes with dual-frequency GPS
#99Earlier quoted context omitted.
I don't really see the strategic importance of 1 meter Vs 1 cm positioning... Is the enemy missile going to miss the bunker because it hit 1 meter off? Or the enemy built their airport 1 meter wonky because they didn't have access to 1 cm level accuracy?
GPS might have been a military invention, but its uses reaches further out today. I think the purpose of Galileo's encrypted GPS is not to prevent military strikes against European nations, but to be able to offer more precision as a commercial service, making a profit. Basically, companies who use GPS for measurements or what have you, can pay money and get access to improved accuracy.
But since GPS is a broadcast service, there is no way to offer encrypted service widely (ie. To a random app which pays for better GPS accuracy) without someone decapping/exploiting a chip in the phone and leaking the rolling encryption key via a web service for everyone.
Re: iPhone 14 Pro comes with dual-frequency GPS
#100Earlier quoted context omitted.
GPS assumes* light travels in a straight line, which it doesn't due to atmospheric effects and reflections off buildings. L5 is a second frequency from the same satellites, which is affected by these problems differently, so the chip can compare the differences between the two signals and guess what's up with the atmosphere and buildings / throw out the dumber looking signal. It's also mostly independent so it's more…
The single frequency situation isn't all that bad though since there are a dozen satellites in view and tracked even in urban outdoor environments.
It's certainly better than it used to be, since there are more satellites, and a lot of work goes into doing well in these environments (I used to do the GPS integration for Google Maps).
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.