Notion of Visibility

Visibility is a natural phenomenon in everyday life. We see objects around us and then decide our movement accordingly. Seeing an object means identifying the portions of the object visible from the current position of an observer. The entire object may not be visible as some of its parts may be hidden from the observer. The observer also determines shapes and sizes of visible portions of an object. Visible portions of an object change as the observer moves from one position to another. Moreover, the observer may see several objects in different directions from its current position; the visible portions of these objects form the scene around the observer. Constructing such a scene continuously is very natural for a human observer as the human visual system can execute such tasks effortlessly.

Suppose a robot wants to move from a starting position to a target position without colliding with any object or obstacle around it. The robot constructs the scene around itself from its current position and then guides its motion in the free space lying between itself and the visible portion of the objects around it. The positions of the robot and the objects can be represented in the computer of the robot by their x, y and z co-ordinates and therefore, the scene consisting of visible portions of these objects can be computed for the current position of the robot.