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Can't use GPS w/o Data Connection?

WiiDSmoker

WiiDSmoker

Suspended
Original poster
Sep 15, 2009
1,891
7,433
Dallas, TX
I have a old iPhone 3G loaded with Tom Tom USA on it. It does not have a data connection...but I'm not understanding why I can't use it?

Every PND out there only has a GPS chip (like the iPhone 3G does); yet I'm unable to use it.

What's the deal?
 
-aggie- said:
That’s not true. You can be in airplane mode and then turn on location services, which will give you GPS access.
Click to expand...

Does not work for me. I have just tried with my 3GS, Airplane Mode on, location services on - TomTom says Poor GPS Reception and just sits there (it isn't at the correct location), Google Maps says "Cannot Determine Location". Upon disabling Airplane Mode, TomTom locks my location in about 30 seconds.
 
tried it on my 3GS, doesn't work for me either w/out some time of data connection; my guess is the internet enabled features inside of tomtom are the culprit here...
 
Carlanga said:
tried it on my 3GS, doesn't work for me either w/out some time of data connection; my guess is the internet enabled features inside of tomtom are the culprit here...
Click to expand...

I'm thinking you're right. There's got to be a work around for this.
 
Wirelessly posted (Mozilla/5.0 (iPhone; U; CPU iPhone OS 4_1 like Mac OS X; en-us) AppleWebKit/532.9 (KHTML, like Gecko) Version/4.0.5 Mobile/8B117 Safari/6531.22.7)

Did you say "No" to it asking you if Tom Tom could access your GPS data? If you did, I think that the location services could be ON and still keep GPS data away from Tom Tom. Make sure that the location services is ON amd the TOM TOM specific location services is ON.
 
Carlanga said:
tried it on my 3GS, doesn't work for me either w/out some time of data connection; my guess is the internet enabled features inside of tomtom are the culprit here...
Click to expand...

Nono, it does work with no data connection (I.e. No sim inserted, wifi off); just not with airplane mode on.
 
The iPhone uses assisted GPS (AGPS). AGPS lets the iPhone cut location lock time by getting GPS satellite constellation data and the correct time from the cellular network.

Without this information the phone needs to wait for the GPS satellites to transmit the data (taking about 12 minutes). This could explain why it is taking so long to get an accurate location lock. When you were trying to get a location lock was it out in the open with direct view of the sky (ala not behind glass or in a building)?
 
TheIguana said:
The iPhone uses assisted GPS (AGPS). AGPS lets the iPhone cut location lock time by getting GPS satellite constellation data and the correct time from the cellular network.

Without this information the phone needs to wait for the GPS satellites to transmit the data (taking about 12 minutes). This could explain why it is taking so long to get an accurate location lock. When you were trying to get a location lock was it out in the open with direct view of the sky (ala not behind glass or in a building)?
Click to expand...

That makes sense.
It probably needs a clear view to the sky and some time to lock in signal.
 
I think there's either a bug in 4.2 or Apple decided that GPS radios don't interfere with airplanes because I just went on a trip this weekend and noticed that airplane mode no longer disables the GPS. If you run something like Loopt that uses GPS in the background, you can clearly see the GPS arrow is still active.
 
TheIguana said:
The iPhone uses assisted GPS (AGPS). AGPS lets the iPhone cut location lock time by getting GPS satellite constellation data and the correct time from the cellular network.

Without this information the phone needs to wait for the GPS satellites to transmit the data (taking about 12 minutes). This could explain why it is taking so long to get an accurate location lock. When you were trying to get a location lock was it out in the open with direct view of the sky (ala not behind glass or in a building)?
Click to expand...

Not true. I used my old 3G with Navigon without a data connection, get a lock within seconds.

I now use my iP4 without a data connection and Navigon finds my location whilst indoors within seconds.
 
pacohaas said:
I think there's either a bug in 4.2 or Apple decided that GPS radios don't interfere with airplanes because I just went on a trip this weekend and noticed that airplane mode no longer disables the GPS. If you run something like Loopt that uses GPS in the background, you can clearly see the GPS arrow is still active.
Click to expand...

your phone will not interfere with an airplane EVER. they will however interfere with cellphone towers. if you are in the air you have the potential to hit more than one cell tower at a time, causing them to reserve cellular channels for your phone. which could prevent others from making calls or dropping their calls.

aircraft are highly advanced. a phone is not going to bring them down. :D
 
itsmemuffins said:
Not true. I used my old 3G with Navigon without a data connection, get a lock within seconds.

I now use my iP4 without a data connection and Navigon finds my location whilst indoors within seconds.
Click to expand...

Your experience versus the original thread author could be explained at least partially by a few components of the iPhones core location service.

One component of the location system in the iPhone is cellular triangulation. Cellular triangulation does not require an active data connection but it does require a sim card because it takes advantage of signal strength and data in the GSM standard. So even without cellular data the iPhone can use this to get a rough location estimate. This differs from assisted GPS where the assisted component does require an active data connection.

Secondly, the GPS satellite constellation data and the correct time are really broken down into two parts, almanac data and the ephemeris data. Almanac data is a rough guide of the GPS constellation and is valid for days to weeks. Ephemeris is more accurate GPS constellation data and is valid for up to 2 hours in a specific location.

So if an iPhone is cold booted or its location services have not been used in a number of days the system may be able to rely on the almanac data and cellular triangulation data to get a rough position. Then it can wait to receive the latest ephemeris data for the satellites above and use this to get a more accurate position lock. But because it already has almanac and cellular data to work with the system may be able to get an accurate lock in under 12.5 minutes versus the 12.5 minutes usually required to receive all of the almanac and ephemeris data.

Both of these aspects could at least partially explain your quick time to position lock, contrast to the original thread author.
 
coochiekuta said:
your phone will not interfere with an airplane EVER.
Click to expand...

"Not ever" is too strong a phrase. Depends on the radios and interference location. Nothing is perfect.

For instance, airline pilots have reported hearing the nasty "GSM buzz" of operating phones over their headsets, which can interfere with hearing ATC.

If you read the anonymous NASA ASRS (Aviation Safety Reporting System) reports, there are instances where pilots have had problems with their instrument landing gear and/or autopilots, causing them to abort landings... and they traced the interference back to someone using their phone in first class. Made the passenger turn off the phone, and all was well again.
 
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