Here is the real story. (iPads only have a compass)
aGPS vs. GPS: The Basics
Okay, first let's do the basic definitions: aGPS = assisted global positioning system, while just regular GPS is non-assisted.
So who's assisting and why does it matter? When you use a GPS system and you turn it on, it needs to find orbit and clock data for the relevant satellites, this in turn results in what is called TTFF, or Time To First Fix how long before you get your location pinpointed. This initial TTFF is often called a cold start and on SiRF III systems (the latest GPS systems available), it can take anywhere from 30 seconds to a couple of minutes to acquire a signal. That time is dependent on your location, amount of interference and horizon information: open fields are faster than canyons or urban environments where buildings can interfere with the satellite-receiver line of site.
But when you use assisted GPS this whole process is much faster. Very often cellular network towers have GPS receivers (or a base station nearby) and those receivers are constantly pulling down satellite information and computing the data. This data is then passed on to the cellular phone (when requested) and acts like a cheat since the relevant satellites to your location are already identified and all that GPS computations is handled by 3rd party computers. This is the result of such a system, to you the end user:
Faster location acquisition
Less processing power is required by the device
Saves battery life
Location acquisition indoors or in non-optimal environmental settings
So with AGPS and a Compass, the iPad 3g has very basic Nav.
dmg
--- In iPad@yahoogroups.com, "David H. Bailey" <dhbailey52@...> wrote:
>
> On 6/25/2011 5:28 PM, Jim Saklad wrote:
> >> David Graham wrote:
> >>> All
> >>>
> >>> IPads do not have a true GPS only aGPS. So having a iPad attached to your dashboard is just going get you a distracted driving ticket.
> >>
> >> I don't understand this statement that they "do not have a true GPS but only a GPS" -- what the heck does that mean?
> >>
> >> And I was under the impression, both from the advertisements as well as from discussions on this list and elsewhere on line that the iPads with 3G were true GPS units and got data from the GPS satellites just the same as dedicated GPS devices do. iPads with just wi-fi don't have true GPS capability, I understand that.
> >>
> >> Is this incorrect information?
> >
> > Although you have partly misinterpreted the other David's statement, the answer here is "yes, this is incorrect information."
> >
> > Wifi-only iPads have no GPS radio and do location services only on the basis of cell towers and Wifi hotspots.
> >
> > 3G iPads have full-fledged GPS radios and can do completely functional GPS geolocation.
> >
>
>
> Huh? That was what I said: " the iPads with 3G were true GPS units and
> got data from the GPS satellites just the same as dedicated GPS devices
> do" and I asked if that were incorrect information, and you just said
> that was incorrect information and then said the same thing I said as if
> it were correct. So how come it was incorrect information when I said
> it and is correct when you say it? I don't understand.
>
> --
> David H. Bailey
> dhbailey@...
>
