GPS is fine for most flights. What if you're in tight surroundings? Let's say you're flying down a long hallway inside of a building. How do you keep the bird from hitting the walls or ceiling? Lidar! My idea is to install six units on the bird. One for each side, top and bottom. Now LiDAR can be used to tell the bird how close it is to a wall. You could plug in say a 2 foot cushion so that the blades never touch the walls. Or if you're in high speed mode approaching a wall of a building, the bird will keep away from the wall.