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GPS use without Internet
- Thread starter marcel500
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GPS has nothing to do with the internet. It uses satellites to triangulate your position.
As far as apps go, not a clue as I don't have an iPhone 3G.
As far as apps go, not a clue as I don't have an iPhone 3G.
except you need internet to get the maps on the phone as they arent stored locally...
On the iphone it does. Without the internet the iphone gps is useless. The gps will show your location as a blue dot but there will be no map loaded.
That is correct....but the internet has something to do with GPS!
I have tried putting my phone in airplane mode and the GPS can't find me. It gives me an error if I try. It can't download the maps anyway so even if it did find you, it would probably not make any sense anyway.
Some people have claimed they can plot a route at home, then turn off the data, and the GPS will follow the cached map...I can't get it to work though.
Maybe you guys could try....try it right now...walk up to 7-11 and get me a slurpee!
I have tried putting my phone in airplane mode and the GPS can't find me. It gives me an error if I try. It can't download the maps anyway so even if it did find you, it would probably not make any sense anyway.
Some people have claimed they can plot a route at home, then turn off the data, and the GPS will follow the cached map...I can't get it to work though.
Maybe you guys could try....try it right now...walk up to 7-11 and get me a slurpee!
Airplane mode turns off the GPS signal as well (at least that's what previous threads have said).
Anyway, like the others have said, at most you'd get a blue dot on no maps.
The iPhone can't find satellites. It relies on the cell towers for that. I know this because I don't have cell service at my house and all it will do is SkyHook location.
Have you tried waiting long enough in a clear open sky area?
Most GPS units take quite awhile after initial power-on to figure out which satellites are where before getting an initial fix. If there's cell service, this is a lot faster on the iPhone, because the phone company can quickly tell the phone which satellites are above the nearest cell tower (and their ephemeris data, etc.) But if there's no cell service, the GPS should still be able to figure it out after listening to all the possible channels and calculating long enough (5 or 10 minutes?).
BTW, a GPS is still quite useful without a built-in map display. The old fashioned way was to take a paper copy of a topo map along, and look up the GPS coordinates on it.
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I know. You should read about how A-GPS works. The cell towers see which satellites are available and when the iPhone needs to use GPS, it queries that information from the cell towers. Without the cell towers, the iPhone is unable to find satellites and thus unable to find its location.
I did word my previous post awkwardly, though.
Yes, it simply will not work. The Maps app shows the spinning thing on the "locate me" button and then after a while it gives me an error message "Your location could not be determined." It just won't work without cell service.
Okay, there are 3 ways the iPhone can locate itself.
1. GPS. The cell towers have a GPS receiver and scans constantly for which satellites are available. It knows, at all times, which satellites are available. When the iPhone wants to use GPS, it asks the cell towers which satellites are available, and uses them to locate itself. Once the iPhone has a GPS "lock" on itself, it can be as accurate as Tom Tom because it works exactly the same way. Once you have a GPS "lock," you can go out of cell range. It no longer needs the cell towers. It only needs the cell towers to create the initial "lock" ... so I can track myself using GPS all the way to my house, but I cannot initiate the GPS tracking at my house. You need cell service to create the "lock."
2. Cell tower triangulation. It asks the cell towers where they are, then it calculates its location based on signal strength to those cell towers.
3. SkyHook. It looks at the MAC address of nearby Wi-Fi signals, then it asks SkyHook where those MAC addresses are located, and it triangulates its location based on signal strength to those Wi-Fi devices. If there's only one signal available, the accuracy is based on signal strength to that device.
I hope this is helpful to those who don't really understand how the iPhone locates itself.
I don't think the iPhone asks the cell towers per se, although it needs a data connection.
It most likely sends its current carrier and cell id as parameters in a TCP/IP query to a common AGPS server, which could be located anywhere. The server looks up what satellites should be in view and sends that info back, along with the location of the tower as a first guess.
At the same time, it looks like the iPhone gets a long term orbit file every two days from an Apple server, to help it search on its own if no data connection is available.
Seems to be based on Global Locate code available on the internet.
It most likely sends its current carrier and cell id as parameters in a TCP/IP query to a common AGPS server, which could be located anywhere. The server looks up what satellites should be in view and sends that info back, along with the location of the tower as a first guess.
At the same time, it looks like the iPhone gets a long term orbit file every two days from an Apple server, to help it search on its own if no data connection is available.
Seems to be based on Global Locate code available on the internet.
Interesting. I was backpacking a few weeks ago (in the mountains, no cell service an entire day), turned on Location Services... after waiting several minutes, one of the iPhone GPS trail/track logging apps started spitting out lat/long coordinates, seemed to report where we were according to comparison with another dedicated handheld GPS.
I wonder whether what you are seeing is a problem with the Maps app, not with the GPS.
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Cool. I don't know exactly how it works, but for all intents and purposes, one could say it asks the cell towers. It must do that (or at least ask through the cell towers) because when I have no service here and I have Wi-Fi on, it still only uses Skyhook to locate me. One would think it could see where I am with Skyhook, and then, through the Internet connection, ask the assistance server closest to me, but that's not the case. I left my phone on for 15 minutes waiting for a GPS connection and it just didn't work.
This "long term orbit file" must be pretty useless, since my phone throws errors when I try to use GPS with no service.
Honestly I find that hard to believe, I've tried all sorts of applications that use GPS and none of them work at my house. I just used "G-spot" and I left it searching for like 15 minutes and it didn't get a connection.
When you try at your house, you're standing outside, right? Satellite GPS doesn't usually work indoors, and often times not even under a thick canopy of leaves (like in the forest).
OK, so when I go to London next year, I'm going to have data roaming turned off, but if there's an app I buy that, say, shows attractions and crap near me (and doesn't require internet connectivity, I know there are a few tourist apps out there like that for various cities) it will still be able to get my location from GPS?
Yeah, I'm in my backyard, no trees, no tall buildings, no mountains. It doesn't work, man.
No it won't. I've tried the speedometer apps. They don't work. The phone is unable to initiate GPS when you have NO SERVICE. But, if you already have GPS going and you drive into a place with NO SERVICE, yes, it continues to work.
I went to Mexico a month and a half ago, had data roaming off and it didn't work. Then I turned data roaming on and it worked. Obviously in Maps the maps didn't show up, but I was using G-spot to see how fast we were going in the taxi cab. It just didn't work.
Honestly it boggles my mind that you guys are trying to refute this. I have several friends with iPhone 3Gs, none of their GPS works at my house unless they track themselves from an area with service all the way to my house.
It's OK to admit that your iPhone is incapable of doing something.
@ General
Unfortunately your speculation is wrong.
"Unlike some phones' A-GPS, Apple implies iPhone's A-GPS will still work without a cell signal"
http://gizmodo.com/5015930/giz-explains-what-you-didnt-know-about-the-iphone-3gs-gps
Unfortunately your speculation is wrong.
"Unlike some phones' A-GPS, Apple implies iPhone's A-GPS will still work without a cell signal"
http://gizmodo.com/5015930/giz-explains-what-you-didnt-know-about-the-iphone-3gs-gps