Tracking hard/software for offline use

This seems like the place to come for some answers. Since I know very little about this, I will start by explaining what I'm trying to accomplish, and hopefully someone can steer me in the right direction. Ideally, I would like to be able to use google earth images and track my location in real time on those images. Yes, I know, that's easy. Here's the catch: I need to be able to do this where there is no cell service, and no internet connection. I'm not opposed to spending some money on this, I'm not looking for a cheap way. The closest I've come is the Garmin 750 Montana, which I would go ahead and buy if only it had a bigger screen, or a way to plug into a larger monitor. My intent is to mount this semi-permanently in a vehicle, and use an external GPS antenna, which also isn't supported by the Montana, although it seems it is quite capable without one. I would like a 7 inch screen minimum, and would prefer a 10", hopefully visible during the daylight. It seems Lowrance offers a device on which I can do this, but I would have to buy maps from Rugged Routes at $120 for each 400 sq. mile grid. The Lowrance runs between $1400-2000. Problems there are I'm paying for a lot of hardware in the lowrance I don't need, and if the guy doing the maps quits doing them, I can't get any new areas.

The only other option I see is to buy a tablet that will accept an external antenna, download a bunch of satellite images on it, and then use software such as Valery Hronusov's app called Navigator to track me on the images. Problem with that is I don't think the app will work on saved maps, I think they need to be google earth images with full functionality.

I've already resigned myself to the fact that I probably won't be able to use Google Earth for this. I currently use an app called OnX offroad, which has pretty good images. I also know of Bird's Eye images, I may end up using those.

Any suggestions, advice, ridicule or comments would be appreciated. The more knowledge I can throw at this problem, the more likely I am to come up with a solution. Thanks in advance!

 

Thank you for that, and what you said makes sense, but there is one problem...I'm not looking for maps as much as I'm looking for imagery. The maps on Open Street Maps show nothing in the areas I'm traveling in. If I could find a way to download and save some high resolution satellite imagery, and plot on that, I'd be in business. Even better would be the high altitude photography that GIS folks use, something like Eagle's View or something like that.
It would probably help to explain what I'm doing with this: My friends and I are retired geology fans, and we take our 4x4s out in the deserts of the Southwestern US looking for areas where minerals and gems might be found. Obviously, abandoned mines are great places to look at the strata of rocks, and are often located quite a ways from the nearest improved roadway. It is much easier to look at the way the rock is laid out with images rather than topo maps. Google Earth is perfect, but as the cell signal dies, so does it's ability to give us accurate images to look at, and none of us have figured out a way to use the images and retain the functionality without a cell signal.

As far as the external antenna goes, I was assuming they would be more powerful and could use more satellites, making it more accurate than the built in antenna, that's all.

What would be perfect is something like the Garmin 700 Montana, only with a screen that's in the 8-10" range so I can see it while driving.

 

Thank you, both of those links have a plethora of useful information. I actually understand the difference between raster and vector images now. The OSMAnd will most likely work best, since small areas are fine...I just need to see if I can find images for the remote areas we are going to, usually many miles from the nearest paved road.
I am familiar with the Birdseye maps, which was another reason I liked the Garmin handheld...you can download and save those maps directly to the device.
Thanks again for the advice and resources, I've got some research and tinkering to do now to see what I can come up with that will be compatible with each other.
As far as the external antenna...am I correct in my assumptions or is the GPS antenna in the tablet going to be just as accurate and robust as an external one? I know I often lose my satellite radio reception in the canyons and forests, I was thinking the GPS would suffer the same fate unless I had a better antenna.

 

Very good, I'll see what happens. I'll get it rigged up and see what happens. Thank you for the input. If anyone else has anything to add, feel free, I'll be checking in to report how it works!