General question about gps

[sonex]

hello everyone,

I am still trying to decide if i should buy the new iphone 3g or try get hold of the 1st gen one for cheaper (in New Zealand). If i do purchase one, it will be on prepay without contract, and quite possibly unlocked/jailbroken.

I cannot figure out from anywhere how this a-gps in the iphone works. People say it connects to wifi and cellphone towers to get your location... Does this mean that gps will work if i am on prepay ?? what if i am in a place where there are no wifi places and my signal is really poor, does the gps get signal straight from the satellite, or can you only get your location in urban places??

hope someone can clarify the whole gps thing for me..

thanks

 

[marksman]

The GPS is a GPS is a GPS.

The GPS in the iPhone works like any other device that has a GPS in it.

Beyond that it can ALSO use cell tower locations and wifi locations to assist in fixing a position more quickly when those resources are available.

When they are not available, the GPS will work like a GPS which is like a GPS.

 

[sonex]

thanx man sounds promising then

 

[joshysquashy]

A-GPS stands for assisted gps, which is better than standard gps.

Standard GPS just uses satellite signals to locate you, and these signals can be bounced off buildings and don't tend to reach inside buildings, you need a direct line of sight with the satellites for them to be accurate. Because of this, it can think you are miles off course when indoors or in a city.

Assisted GPS not only uses GPS, but cell towers and wifi networks to confirm your location. It uses the best available method to pinpoint your location. GPS is most accurate so this is used when reliable, and is accurate to within meters. All you need to know is it shows a point (where you are) with a circle around it, the accuracy of where you "could" be if it got it wrong! So a small circle means its fairly accurate, a large one isn't so accurate.

Most of the time its GPS, especially outside or in a car. With A-GPS you get the best of both worlds.

 

[sonex]

i've just been reading around the forums and someone said that you still need to be on a data plan to download the maps :/
so if i just turned on the iphone out of the box and the phone has no pre loaded maps, my location will be found in a "yellow desert" with no roads etc??

Is it possible to go home and download the map of the whole country through your own wifi , and then have everything pre loaded for when you actually go out?

--all this considering i will be on prepay with no data usage etc.

 

[michail]

Also I believe when the A-GPS uses the cell towers to locate you it will also exchange data so if you do not have a data plan you will get changed from your provider for downloading/uploading data. So in other words you will get changed for it!