Hi All, I'm currently in Europe and I'm having problems with the GPS; it is not working at all. I cannot get a location in any of my Apps with it. Whenever I try to use it, it searches for a minute and then I get a message saying "Your location could not be determined". I do have data roaming turned off, but I don't think it should matter for the GPS, I've used the GPS with the phone on airplane mode in the US before, and it's not working when I am connected to wifi.
As I understand it, the iPhone 3G has what's called "assisted" GPS, which should probably be renamed "reliant" GPS. You can read some Wikipedia articles about AGPS for more info, but the gist is that a completely stand-alone GPS receiver usually takes several minutes to get its first location fix because it needs to download fresh info from the satellites which by-design happens on their slowest data link.
To save you having to sit there in Maps for several minutes, the phone relies on extra help from the cell-towers nearby. It sends fragments of the messages it's getting to the cell towers, which themselves have GPS receivers, and the towers send back the completed data. That saves the iPhone from having to download all the satellite info itself.
To the best of my knowledge, this requires an active cell data connection, so if you're roaming and data roaming is turned off, you won't get the "assistance" from the cell-towers. Also, as I understand it, and from personal experience, the iPhone is reliant on this assistance and won't fall back to downloading all the necessary data from the satellites over the 5-10 minutes it would take.
If you're connected to a WiFi hotspot through which you can actually browse the web (i.e. not just redirected to a login page), then you ought to still get a rough location fix via the Skyhook service. No hope for GPS though, as it requires the cell-towers specifically, not just any internet access.
thats not true... you can reset the iphone to FACTORY SETTINGS takes 2 hours but as u have not backed up from new purchases and stuff i dont suggest u do that
By the way, I have gotten a few responses saying that the GPS does not work in airplane mode. My GPS is working again, and so I thought I would show you all that I was not wrong and I was not imagining things.
notice in this screen shot of my basic GPS app that airplane mode is on. Also it's not even connected to wifi.
this is a screenshot from the maps app. The map and directions were loaded with wifi, but even after I left the wifi connection, and closed the app, when I started it again (with no data connection and in airplane mode) it still show my current location and position on the map, not just thw start and end points.
Ostiarius: I'm very interested in your experience because I'm going to Africa in a few months and want to use my iPhone's GPS to obtain Latitude and Longitude coordinates for some locations there. I don't want to pay roaming charges and probably there won't be any wifi available. Mapping is totally unimportant to me at the sites, but later I will use maps on my laptop where there will be wifi available. My understanding is that with Basic GPS or GPS Ally I can do this. I have been experimenting with it at my home and indeed it works OK. Unfortunately when I put it in airplane mode and turn wifi off I get a message on Basic GPS that it cannot locate my position and asks if it's in airplane mode. When I turn on wifi but leave it in airplane mode I do get a position and no error message. But is this using GPS (it appears not to be as accurate)? I will contact the developer when I have more time and get his comments on it (I have contacted him before).
Ostiarius: I should have added, in Africa I will use it with airplane mode off, and that's the way I have mainly been testing it here. I put airplane mode on just to duplicate your conditions.
I'm not 100% sure what to tell you because I'm still not sure why sometimes this works for me and sometimes it doesn't. It worked ine in the US, but then stoped when I got to Europe, and then all of a sudden started working again while still here in Europe. When it wasn't working, it didn't even work with Wifi. So I don't know.
As far as the accuracy goes though, I think it is pretty accurate. In the Basic GPS screen shot it shows that is has a radius of 300 feet, but you can see from the upper right hand corner that it's still acquiring the position, and as for the Maps screen shot it shows pretty much my exact position at the time. As you can see I was off the route that the phone set for me, but that was intentional as I decided to walk along the canal rather than the small back road the map sent me on.
