The Garmin etc are true GPS devices with multi satellite receivers. The iPad GPS is piggybacked onto the cellular chip. It doesn't use cellular data, but does use a combination of satellite and cellular tower signals for positioning. It also uses the cellular antennas for GPS. I suppose Apple could use stand alone GPS receiver chips but the cost with antennas would probably approach that of the cellular chips.
iPads and iPhones now have GPS receivers that receive signals from both the American satellite navigation system - commonly called GPS, and the Russian GLONASS system.
So, they are pretty capable receivers.
Your response makes it seem as if the iPhone and iPad GPS receivers don't work well when there is not a cell signal present.
As I'm sure you know, this is hardly the case. They work perfectly fine when there is no cell signal. People use them every day in the wilderness and at sea.
How expensive would it be to just include the combined cell/GPS chip and disable the cell part of it in non cellular devices?
Some of the navigation apps are pretty expensive, and Apple would conceivably make the money back from their cut of the app sales.
iNavX for example is $50 in the app store.
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If you only want position, speed, and direction, which is fine for navigation, in combination with charts, MotionX will be fine. If you want surface map data, such as with Google maps, then you need a wifi or cellular connection.
again..., there are _many_ apps that store the maps and charts locally on the device. MotionX is not the only one.
I own quite a few of them.
I have hundreds of dollars invested in navigation apps and the charts that i had to buy for the apps.
I'm pretty familiar with what's out there.