Jamming or spoofing the GPS- (and most likely also other GNSS) signals near military bases would seem very logical to me and is very much possible from a technical standpoint. Also, officially documenting such security measures would be highly counterproductive.
Although losing the lock only when making fast loops seems somehow odd, maybe you lose control ...
OruxMap is one of the best android apps for navigation. You can get an approximate altimeter using device barometer Compass, you can use it for navigation, save your tracks, waypoints and POIs, and many more. It is free.
Maybe your can try the try and except condition to make sure where things goes wrong. Something like this :
while n<3600 :
whatever condition you want to test
At least if it still doesn't work it should not freeze anymore.
GPS accuracy varies based on several parameters, most important the number of satellites you can get signals from, and their geometric distribution on the sky.
Some factors affecting this are:
Line-of-sight. You need line-of-sight to the satellites to get any useable signals. Different locations will have different horizons (i.e. a hill, mountain or ...
The approach you're looking for is called monoplotting in photogrammetry.
If given your assumptions on camera orientation, you will need a digital elevation model (unless you also assume the ground is perfectly flat), and also the size of your camera's imaging sensor.
I'll try here to describe a simplified version of this process.
Given the position (I ...