Q: Does iPad 2 WiFi Really Have No GPS???

According to several web sources, the iPhone and iPad do indeed support cell tower triangulation, or at least they did.

http://www.edepot.com/iphone.html#iPhone_A-GPS

I'm not saying these guys and others are right and maybe there are major differences in iPhone and iPad for some of these features (although I highly doubt it), but I've read it in multiple places.

Adding more confusion is the NASA web page the very explicitly describes A-GPS as a "service" of DGPS. The link that you provided does not reference DGPS at all. I'm awaiting Chris' response to my later message to him. My hunch is that the author of the doc you referenced was unaware of DGPS and incorrectly concluded that cell tower triangulation is used.

To be fair, the NASA article simple states:

"Assisted-GPS (A-GPS) data – provides data and information about the GPS orbit and clock states that allow cellular phones to pinpoint their location on phone map applications and when making emergency 911 calls"

It does not say that aGPS is a feature of the DGPS system. aGPS was developed by communications companies and (Lucent and Qualcomm being amongst the biggest players in it's development, as well as companies rapidly bought up by Qualcomm). aGPS is a feature of the cellular carrier network, not the GPS infrastructure per se. The "assisted" in aGPS has meant a number of features implemented over the years since the early 2000's that improve the speed and accuracy of a location fix.

Now, what is the signal flow for A-GPS? I'm thinking that the DGPS ground station transmits not only the GPS error information but also its own location. >This is received by the cell towers and, after signal conversion, is retransmitted out to the cell phones and similar devices

I don't believe the DGPS data is transmitted over A-GPS. It may be used to "adjust" its own location when this is sent to the cell phone.
The 911 services will get a call and get the GPS location from the device. The DGPS data will be used by 911 to calculate the corrected location.

As soon as I turn my device on, it takes the A-GPS information to use as a "ballpark" estimate of its own location. That, in turn, makes it easier to locate the visible satellites. Close?

The cell tower sends out A-GPS of its own location info and the cell device will calculate a position. With multiple cell towers, it will be more accurate.
And yes, once a known position is established, the satellite data can be more quickly acquired.

According to several web sources, the iPhone and iPad do indeed support cell tower triangulation, or at least they did.

Yes they do but that has nothing to do with A-GPS (or any GPS).
All you need is a compass and a cell network receiver.

Michael Black wrote:
To be fair, the NASA article simple states:

"Assisted-GPS (A-GPS) data – provides data and information about the GPS orbit and clock states that allow cellular phones to pinpoint their location on phone map applications and when making emergency 911 calls"

It does not say that aGPS is a feature of the DGPS system. aGPS was developed by communications companies and (Lucent and Qualcomm being amongst the biggest players in it's development, as well as companies rapidly bought up by Qualcomm). aGPS is a feature of the cellular carrier network, not the GPS infrastructure per se. The "assisted" in aGPS has meant a number of features implemented over the years since the early 2000's that improve the speed and accuracy of a location fix.

I didn't say "feature." I said "service." You might wish to read the entire page. The following is a C&P from that page. The italics and bolding are mine.

+The GDGPS System is supported and funded by its many civilian and military users who benefit from its high accuracy correction message, as well as other real-time GPS data and positioning services it provides. *Some examples of GDGPS services include:*+

+GREAT ALERT – a natural hazard alert system, which was recently successful in predicting the size of the tsunami triggered by a magnitude 8.8 earthquake off the coast of Chile in February 2010.+

+*Assisted-GPS (A-GPS) data – provides data and information about the GPS orbit and clock states that allow cellular phones to pinpoint their location on phone map applications and when making emergency 911 calls*+

+Real-Time positioning – with the user module of the RTG software, users can determine their precise location and time whether they are in space, in the air, or on the ground.+

I'm getting a headache. I yearn for the good old days and slide rules!

I'm getting a headache.

That would be A-HEADACHE.

Touché!

The real question for me is: If I buy a Wi-Fi-only iPad (no 3G) and tether it to my iPhone to gain 3G access, will the iPad use the GPS on the iPhone for the apps that requir Location Services?

Hersco wrote:
The real question for me is: If I buy a Wi-Fi-only iPad (no 3G) and tether it to my iPhone to gain 3G access, will the iPad use the GPS on the iPhone for the apps that requir Location Services?

No. But then, if you have an iPhone, you could just as well install the same app to the iPhone. Most likely an iOS app that like that which uses GPS would be iPhone and iPad compatible (or have versions for both.)

Not to my knowledge.

The wifi version uses wifi signals and some sort of triangulation to get your location.

Correct. The WiFi only apple devices use WiFi triangulation to get an approximate location - they use technology from SkyHook (or at least they used to) - http://www.gpsbusinessnews.com/iPhone-gets-Wi-Fi-positioning-from-Skyhook-Wirele ss_a603.html

they use technology from SkyHook (or at least they used to)

As of iOS greater than 3.1, (April 2010) iOS devices use an Apple database.
-> TechCrunch - In April, Apple Ditched Google And Skyhook In Favor Of Its Own Location Databases