OK, lots of good questions, that I don’t have all the answers to.
Not battery powered would be hardwired to a PC. It could possibly be Bluetooth…
The GPS ‘signal’ would be from a computer running a simulator that can output a a data string likely through an old serial output or something. I’m honestly not sure what the data string format would be at the moment, still working that out - Possibly something like NMEA, maybe something as simple as a text string with the data I need, but in a different format.
Either way it would likely have to undergo some manipulation as it is likely not in the format recognized by the app. The app needs a 1Hz string with Lat / Long / Altitude / Track / Ground Speed and some other line identifiers.
The key here is making the hardware interface that can take the data string, do a manipulation to it, then send it off via wifi or bluetooth that can be picked up by an iPad thats a few feet away.