There are also terrain and weather conditions. Typically it is very hard to glide at night since a large part of gliding is the air movement caused by local an

There are also terrain and weather conditions. Typically it is very hard to glide at night since a large part of gliding is the air movement caused by local and regional thermal differences. Ardupilot (or one of its offshoots, I can't recall exactly) does have a lift detecting autopilot in beta. I don't know how it works with a specific route, but it seems to lock in thermals pretty well.