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iPhone A-GPS --- works without mobile network?!

randfee2

randfee2

macrumors 6502
Original poster
Jun 13, 2007
270
233
Germany
Yes, I do know what assisted GPS means and how it works. It speeds up position locking when turned on significantly. What I don't know is how the iPhone has this implemented.


Question:
Can the iPhone GPS operate WITHOUT a cellular network. It will take longer, granted, but will it get a fix or not? This is very important, since there is gonna be navigation-Software like TomTom & Navigon. What if you're in an area where there is no service?! If its strictly A-GPS, depending on a mobile network to get a lock at all, it wouldn't work, which would be unacceptable for a navigation-system!


There must be some 3G users that have used offline maps or some geocaching app that were out of coverage areas?! Did it work or not?
 
rorschach

rorschach

macrumors 68020
Jul 27, 2003
2,272
1,856
randfee2 said:
Yes, I do know what assisted GPS means and how it works. It speeds up position locking when turned on significantly. What I don't know is how the iPhone has this implemented.


Question:
Can the iPhone GPS operate WITHOUT a cellular network. It will take longer, granted, but will it get a fix or not? This is very important, since there is gonna be navigation-Software like TomTom & Navigon. What if you're in an area where there is no service?! If its strictly A-GPS it wouldn't work, which would be unacceptable!


There must be some 3G users that have used offline maps or some geocaching app that were out of coverage areas?! Did it work or not?
Click to expand...

As far as I know, it'll work. I've fired up Maps before with no internet connection and gotten the blue dot (just with no maps overlay, only the grey grid.) TomTom will have built in maps, so I assume it could just use the location alone + overlay its own (locally-stored) maps.
 
M

Michael CM1

macrumors 603
Feb 4, 2008
5,681
276
I'm 99 percent sure that AGPS is the same exact thing that Garmin, Magellan, TomTom, etc. use in their units without a cell network. The GPS radio talks to the satellites for all the information. The Internet connection would probably be used for things like map updates, but I don't think being outside a cell coverage area will affect any GPS app at all.
 
gloss

gloss

macrumors 601
May 9, 2006
4,811
0
around/about
Michael CM1 said:
I'm 99 percent sure that AGPS is the same exact thing that Garmin, Magellan, TomTom, etc. use in their units without a cell network. The GPS radio talks to the satellites for all the information. The Internet connection would probably be used for things like map updates, but I don't think being outside a cell coverage area will affect any GPS app at all.
Click to expand...

A-GPS uses a cellular signal to get info on where in the sky to look for the nearest satellites.

There is no 'talking to' the sats. They simply transmit an incredibly weak stream of bits that the radio picks up and uses to triangulate a position. If left to its own devices (i.e. non-Assisted GPS) it can take up to a few minutes to get a fix.
 
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