iPad 3G question

[kjk]

Originally Posted by Maggie Leung

So when my car GPS is connecting to a satellite, what kinda communication is it using?

GPS!

[Maggie Leung]

Originally Posted by kjk

GPS!

Lol. I think I need an interactive book to explain GPS to me.

[Rob_E]

Originally Posted by Maggie Leung

By the way, so how does a GPS (the kind for your car) work?

My understanding, and I'm no expert by any means, is that GPS in your car and GPS in the iPad/iPhone or in any GPS receiver work using similar chips and by the same method which is:

GPS locates satellites and "pings" them by sending a little packet of information to the satellites and then seeing how long it takes for the signal to come back. Then it does a lot of fancy math to figure out where you must be in relation to those satellites to account for the time differences in the return signal. If it can locate enough satellites, it can give you a pretty precise set of co-ordinates.

[kjk]

http://www.rfidc.com/docs/gps.htm

It is kinda hard to believe it is "free", actually.

[Maggie Leung]

Originally Posted by Rob_E

My understanding, and I'm no expert by any means, is that GPS in your car and GPS in the iPad/iPhone or in any GPS receiver work using similar chips and by the same method which is:

GPS locates satellites and "pings" them by sending a little packet of information to the satellites and then seeing how long it takes for the signal to come back. Then it does a lot of fancy math to figure out where you must be in relation to those satellites to account for the time differences in the return signal. If it can locate enough satellites, it can give you a pretty precise set of co-ordinates.

So reviewing to make sure I understand:

If you have a GPS chip in a device, it can locate itself on maps stored on your device. And even without wi-fi or 3G, your GPS chip can communicate with satellites, and between the two, they triangulate your position and can use existing stored maps to figure out where you wanna go next?

[kjk]

Originally Posted by Maggie Leung

So reviewing to make sure I understand:

If you have a GPS chip in a device, it can locate itself on maps stored on your device. And even without wi-fi or 3G, your GPS chip can communicate with satellites, and between the two, they triangulate your position and can use existing stored maps to figure out where you wanna go next?

Exactly.

[Maggie Leung]

Cool. Thanks to everyone for explaining. Never thought through how GPS works before. It still seems pretty magical, lol.

[murraypaul]

Originally Posted by Rob_E

I seem to remember that, for the iPhone at least, there was a program that would download the relevant maps to your phone so that you would have them even if you were in a poor/no AT&T reception area.

Offmaps does this, and is available on both iPhone and iPad.

[rkelac]

Originally Posted by Rob_E

My understanding, and I'm no expert by any means, is that GPS in your car and GPS in the iPad/iPhone or in any GPS receiver work using similar chips and by the same method which is:

GPS locates satellites and "pings" them by sending a little packet of information to the satellites and then seeing how long it takes for the signal to come back. Then it does a lot of fancy math to figure out where you must be in relation to those satellites to account for the time differences in the return signal. If it can locate enough satellites, it can give you a pretty precise set of co-ordinates.

Nope. A GPS receiver is only a receiver. It does not transmit up to the satellites.

[HarryT]

I was under the impression that the type of GPS used by the iPhone worked by triangulating your position from the signal strength of different local telephone "cells". I don't believe (and please correct me if I'm wrong) it involves GPS satellites at all.

[Mike_73]

Originally Posted by kjk

http://www.rfidc.com/docs/gps.htm

It is kinda hard to believe it is "free", actually.

It's kinda free allthough I bet that license fees are included in the purchase price of any device incorporating GPS (just like the fees included in the final product price you have to pay in Germany for printers, CDs, DVDs, etc. as you could copy them or use them to create copies).

[tbergman]

Originally Posted by HarryT

I was under the impression that the type of GPS used by the iPhone worked by triangulating your position from the signal strength of different local telephone "cells". I don't believe (and please correct me if I'm wrong) it involves GPS satellites at all.

Nope, both the iPhone and the iPad 3G use the satellites for positioning information. I believe that the iPad (non-3G) does do something like what you describe. I'm not sure if the iPhone/iPad3G also take advantage of the cell phone system when in areas (like tunnels) where the satellites can't be heard.

Just found an interesting article from Apple on how location services work on the iPad.
http://support.apple.com/kb/HT4084

[tbergman]

Originally Posted by Mike_73

It's kinda free allthough I bet that license fees are included in the purchase price of any device incorporating GPS (just like the fees included in the final product price you have to pay in Germany for printers, CDs, DVDs, etc. as you could copy them or use them to create copies).

Only if you consider the taxes we Americans pay as a "fee" for the GPS system. The GPS system was built and paid for by the American military.

For further detail, I suggest this wikipedia entry http://en.wikipedia.org/wiki/Global_Positioning_System

[HarryT]

Thank you for the correction. Very interesting!

One obvious point: the WiFi version of the iPad obviously can't use 3G cell tower triangulation, since it contains no 3G radio . It (and the iPod touch) do use a form of positioning which appears to involve knowledge of the geographical location of WiFi networks.

[BenG]

Mobileread member DaleDe has a GPS website.
His article on how GPS works:
http://www.gpsinformation.org/dale/theory.htm