I do not really know the code of Ardurover, and so, the github program linked above may not be what is running in Ardurover, but the link did come from Ardupilot docs. And my experience has been that the rover does try to get back to the line.
I will add that tuning is very hard. You have to tune: speed, steering, pivot turns, and overall navigation systems. There are interdependencies. The control loops are not simple PID loops. Some of them have a feed forward term. There are additional terms, etc.
I may be wrong but I think that the control system could be simplified for a Rover. The complexity may be necessary for a flying vehicle. BUT, keeping as much of the code as common as possible between the different versions is an overarching goal, I am sure. So, no complaints from me! Hats off to all those who have built this great system!
