We are talking about iPads here so some of your comments dont apply. I've added my follow-up comments in Bold to add clarity.
If you have a 3G iPad you DON'T need any additional gps hardware.True, however, a lot of people are still adding a bluetooth GPS puck to the 3G ipads. With the addition of a bluetooth GPS either unit (3G or wifi only models) can be used for off road navigation with out worrying if you will have cell coverage. IMO this negated the need for a 3G model ipad. Adding a bluetooth GPS puck is redundant on a 3G iPad unless you have an install where the Ipad cannot get a GPS signal. Having all of the hardware in one package seems like a cleaner and less cluttered way to go having to only power the iPad for the GPS signal and functionality. 3G/GPS model iPads are $130 premium over Wifi only units, and BT pucks are anywhere from $50 to $130. Adding a bluetooth GPS puck to any iPad you are simply providing a GPS signals to the unit, it adds no additional functionality to a 3G/GPS iPad. Of course either unit can be used for offroad navigation.
There are 3 types of apps you can use on the iPad.
Apps that are 3G dependent like Google Maps. No coverage no mapping. Not true. If you have a gps puck like mentioned above, you can use the ipad to locate yourself in google earth. In order to use the high res images found in google earth you can download the area you will be traveling ahead of time and store them in the cache for use when no coverage is available. Pretty cool actually. People have been doing this for years with laptops... Actually true, you are talking about a different app which falls into category 2, "Apps that can cache maps for offline/no coverage like Motion X GPS HD. You download area maps via 3G or wifi prior to loss of coverage or during per planning of the trip.". My example was Google Maps, Built-in to iOS and it does not cache maps offline.
For example: GooPs Technologies | GPS Tracking and Navigation for Google Earth This is a plug-in for GE to be used with a laptop not an iPad
Apps that can cache maps for offline/no coverage like Motion X GPS HD. You download area maps via 3G or wifi prior to loss of coverage or during per planning f the trip.
Apps that carry all the mapping in memory like ScenicMaps. All maps Are ready to go.
The last two types are suitable for off road / remote area navigation. See above if you want to use google earth.This is a plug-in for GE to be used with a laptop not an iPad
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