Will any of the Garmins have better GPS than phone?

[pluton]

Most of the time, the Gaia app on my iPhone is accurate enough for my amateur purposes. However, I have occasionally gotten a false location from an iPhone Xr running Gaia. It's unknown to me how much is iPhone/iOS, how much the Gaia app, and how much is the interface between the two. I have never [that I know of] gotten false location with either of the 2 modern Garmin units I've owned, Montana 650T (2011) and the new Montana 700i(2021). Most recently, in March of 2021, it took the Gaia app about 24 hours to finally stop telling me that I was ≈30 miles away from where I knew I was. Very annoying.

 

[Roaddude]

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From an informative page about this (with a really lousy click-bait type title):

"The iPhone relies on an internal Assisted GPS (AGPS) chip to determine your location. This feature comes built into your iPhone so you don't even need to install it. This system is faster than traditional GPS, since it creates an approximation of your location based on satellite information."
.

 

[roving1]

Most of the time, the Gaia app on my iPhone is accurate enough for my amateur purposes. However, I have occasionally gotten a false location from an iPhone Xr running Gaia. It's unknown to me how much is iPhone/iOS, how much the Gaia app, and how much is the interface between the two. I have never [that I know of] gotten false location with either of the 2 modern Garmin units I've owned, Montana 650T (2011) and the new Montana 700i(2021). Most recently, in March of 2021, it took the Gaia app about 24 hours to finally stop telling me that I was ≈30 miles away from where I knew I was. Very annoying.

My vote goes for entirely iPhone nonsense.

 

[Bill Ruttan]

This is wrong on so many levels. Yes, most phones have an actual GPS receiver, they work just like a standalone GPS when you don't have cell service. When you do have cell service, the phone GPS works better than a standalone GPS as it can also use the cell service to sync time and ephemeris data. GPS is not blocked for security reasons, and that would be pointless as there are several other GNSS services (Beidu, GLONASS etc) that you could use if GPS were blocked.

Maybe not “blocked”, but does not the U.S. Government still have the ability, when deemed necessary, to degrade the accuracy (Selective Availability) of its GPS (Navistar?) system?

 

[pluton]

Maybe not “blocked”, but does not the U.S. Government still have the ability, when deemed necessary, to degrade the accuracy (Selective Availability) of its GPS (Navistar?) system?

They could scramble/degrade the accuracy of the signals, but there is now so much civilian commerce based on the availablilty of GPS that if the DOD did it, they'd have the people of multiple nations screaming at them. They're trapped. I recently read that they are building a a new constellation of satellites with additional signals that won't be made available to civilians

 

[ITTOG]

Maybe not “blocked”, but does not the U.S. Government still have the ability, when deemed necessary, to degrade the accuracy (Selective Availability) of its GPS (Navistar?) system?

I think this is primarily done only on elevation. I don't recall reading about them doing it on long/lat.

 

[axlesandantennas]

I think this is primarily done only on elevation. I don't recall reading about them doing it on long/lat.

This article is a little dated, from 2014: https://insidegnss.com/u-s-eases-export-regulations-for-gps-receivers/

Basically it states that NAVSTAR GPS enabled civilian receivers that were capable of 60,000+ of elevation and 1000 knots speed were considered restricted. But this article states that it has been lifted to some degree.

Not quite what you were referring to with SA, but same ball park.

Now, in reference to SA : https://www.gps.gov/systems/gps/modernization/sa/

Note that they say they will never use SA again. To me, that could me a few things. Such as "we will call it something else", or that their new blocks of GPS sats will have an encrypted signal (P/A) much more robust than what was previous.

Remember a few years ago when the Iranians spoofed the GPS signal of a stealth drone? I personally think spoofing is a much more important issue than absolute position. I can't remember the article, but I also seem to remember that the military has the ability to degrade GPS signals over a specific area, but I cannot work that out how that would work, considering the huge foot print a GPS has at 12,500 miles.

 

[DaveInDenver]

I think this is primarily done only on elevation. I don't recall reading about them doing it on long/lat.

They can't selectively degrade just altitude. GPS is inherently less accurate determining altitude so the added error will compound, though.

They could scramble/degrade the accuracy of the signals, but there is now so much civilian commerce based on the availablilty of GPS that if the DOD did it, they'd have the people of multiple nations screaming at them. They're trapped. I recently read that they are building a a new constellation of satellites with additional signals that won't be made available to civilians

As of Block III GPS procurement they actually will not be able to degrade GPS. It was intentionally removed from the specification going forward. As of SVN 74 and newer (launches since 2018) it's not even an option on the satellite and so it's reasonable to expect it'll never be turned back on.

That's not to say GPS will always be available and correct at your location but the original method of intentionally degrading the whole constellation won't be used. Or that there's not other issues. One I just read about a couple of months ago is a side effect of trying to harden against electronic warfare is that jamming and spoofing testing has been creating havoc.

https://spectrum.ieee.org/aerospace...-to-airline-safety-the-us-militarys-gps-tests

 

[axlesandantennas]

Most of the time, the Gaia app on my iPhone is accurate enough for my amateur purposes. However, I have occasionally gotten a false location from an iPhone Xr running Gaia. It's unknown to me how much is iPhone/iOS, how much the Gaia app, and how much is the interface between the two. I have never [that I know of] gotten false location with either of the 2 modern Garmin units I've owned, Montana 650T (2011) and the new Montana 700i(2021). Most recently, in March of 2021, it took the Gaia app about 24 hours to finally stop telling me that I was ≈30 miles away from where I knew I was. Very annoying.

I had this problem once and took about 30 minutes to get it to stop. Basically, what I could figure out, was that a cell phone tower was causing some signal misunderstanding (refer back to A/GPS). What I finally did was swipe up to close Gaia and then turn the cell phone part of the iphone off. I seem to recall instructing GAIA not to work with the cell portion either. Fixed it right up. But it was frustrating. Had I NOT been in an area I was familiar with, I dare say that this could have led to me getting lost.

 

[DaveInDenver]

I had this problem once and took about 30 minutes to get it to stop. Basically, what I could figure out, was that a cell phone tower was causing some signal misunderstanding (refer back to A/GPS). What I finally did was swipe up to close Gaia and then turn the cell phone part of the iphone off. I seem to recall instructing GAIA not to work with the cell portion either. Fixed it right up. But it was frustrating. Had I NOT been in an area I was familiar with, I dare say that this could have led to me getting lost.

Doesn't Gaia use the iOS Location Services? I doubt it has the ability to select a source down to that level. If the iPhone is getting erroneous information triangulating from a badly configured secondary terrestrial source then the whole phone will likely be confused. Could try putting the phone into airplane mode to force it to rely on satellite-based sources. That'll be accurate unless the root cause is a local multipath or interference, in which case there's not much you can do.

 

[greg.potter]

Most recently, in March of 2021, it took the Gaia app about 24 hours to finally stop telling me that I was ≈30 miles away from where I knew I was. Very annoying.

That does sound like app that has stopped or hung up. Did the position resolve on it's own or did you have to re-start your phone?

I have notice that my Garmin GPS is a bit more accurate and sensitive than my Motorola phone, but I tend to use my phone more because the screen is easier to read. If I am navigating in particularly tricky conditions (think whiteout conditions skiing across a glacier) I will default to the Garmin.

 

[ITTOG]

They can't selectively degrade just altitude. GPS is inherently less accurate determining altitude so the added error will compound, though.

That is not correct, or at least it wasn't. About ten years ago I remember an article where they were purposely causing altitudes, longitudes, and latitudes to be inaccurate by any factor they input. So the capability is definitely there but that doesn't mean they do it.

 

[DaveInDenver]

That is not correct, or at least it wasn't. About ten years ago I remember an article where they were purposely causing altitudes, longitudes, and latitudes to be inaccurate by any factor they input. So the capability is definitely there but that doesn't mean they do it.

I'd be very interested where you read this. Selective Availability introduced both delta and epsilon error to create geometric error, which understanding I'm definitely not an orbital mathematician, I understood meant an increase in VDOP can't happen without a correlating (and characterizing) one in HDOP and TDOP. Therefore while it might be possible to exploit the calculation in theory to give a different vertical error than you'd expect in horizontal I think it would then deviate from a normal spherical error probable and would be a deterministic clue to how you introduced the error.

 

[Rando]

Maybe not “blocked”, but does not the U.S. Government still have the ability, when deemed necessary, to degrade the accuracy (Selective Availability) of its GPS (Navistar?) system?

As DaveInDenver points out, this capability is no longer built into the satellite constellation. Secondly, it would be pointless, as nefarious users could easily switch to one of the other GNSS systems which the US does not control.

 

[ITTOG]

I'd be very interested where you read this. Selective Availability introduced both delta and epsilon error to create geometric error, which understanding I'm definitely not an orbital mathematician, I understood meant an increase in VDOP can't happen without a correlating (and characterizing) one in HDOP and TDOP. Therefore while it might be possible to exploit the calculation in theory to give a different vertical error than you'd expect in horizontal I think it would then deviate from a normal spherical error probable and would be a deterministic clue to how you introduced the error.

I will see if I can find it but given it was so long ago I doubt it. The premise was we were at war and we did not want an enemy to use the data against us for their bombs. So they talked about manipulating the GPS coordinates so the bombs would only go to locations of no impact. Our systems would have the data to adjust for this.

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