Due to the number of different tile states in which intersections must
be negotiated, rules for intersections are encapsulated in robot
states.
Figure 11 Figure
shows the robot states used to
negotiate intersections by turning left, turning right, and going
straight. By convention, the robot is always in the Robby state
when no subgoals have been established. Each of the transitions from
the Robby state in the figure establishes a subgoal; as the robot
traverses the tile, the robot state is updated to reflect its
progress. This allows the tile stateset to be smaller, as
it is not necessary to use additional tile states to track this
progress.