I’ve been out of quads for a few years. I had a near disaster with a large quad that went rogue, it went about 1/2 a mile off course, but it somehow miraculously came back and crash landed near the launch point. I suspect something with the internal magnetometer may have been part of the cause. FC was a HK32 pixhawk knockoff and I often got compass calibration errors. But sometimes it would work perfectly fine on long mission paths (maybe a mile round trip).
But I’ve been thinking about how to have a good backup for RTL. Could you have the quad take pictures, say pointed down. And then if GPS/compass/radio fails, it could try to back track via the picture history back to launch?
I know photogrammetry takes a lot of computing power, so it would have to be some algorithm that a small Raspberry PI could handle.
I was also wondering if a system could be built that had preloaded Google earth images to allow navigation from just the loaded pictures and an onboard camera. Obviously sun/clouds/seasons/time of day could screw all that up.
I’ve been trying to catch up on all the latest. It seems some Non-GPS navigation is done by just counting up all the accelerations/speeds to figure out where it is, but that seems error prone to me.
Probably way over my head to develop something like that, so maybe somebody else has done it or tried it.