When it's time for a drone to fly itself home, we for years settled for a a straight line back, "as the crow flies". That's obviously inadequate, since there could easily be a tree or large building in the way. So 3DR improved that with Solo, with the "Rewind" feature, which finds the shortest path back through the known-good area that the drone has already flown through.
Now that same technology is coming to the open source PX4 flight code. A preview is shown above. Smart.