1. a robot walks through the black path and will detect and avoid the obstacles.
2. a person walks around the trees.
Having eight proximity sensors around the robot, the robot can detect if there is obstacle and keep away from it. And for the three light sensors on the robot, it can detect the black path, they go white or black depending if it sees a line.
The camera in front of the robot can shows the view to user so we can see if there is obstacle or not.
For drawing a black path, tab the button "toggle path edit mode" to add and move the path point, and to let the light sensors can be more easily to detect the line, I change the line size to more thicker in the properties surface.