Page 362 - Introduction to AI Robotics

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Hybrid Architecture
9.5 Case Study of Topological Navigation with a
are used to specify and carry out the implied details of the plan in a modular
and reusable way.
The implementation consisted of three scripts for navigating doors, halls,
and foyers. The pseudocode for navigate-door is shown below in C ++
style and takes advantage of the indexing properties of the switch statement:

switch(door)
case door-not-found:
//initialization phase
//follow wall until find door
if wall is found
wallfollow to door
else
move-ahead to find a wall
case door-found:
//nominal activity phase
move-thru-door(door-location)

The nominal behavior, move-thru-door, is self-terminating, so there is
no separate termination condition. The perception of the door is the key
determinant in what the robot does.
The navigate-hall is used for traveling between corridors, foyers and
corridors, and from corridors to corridor/door nodes. It has two different
starting conditions. One condition is that the robot is in a foyer and detects a
hall. Since the hall may be somewhat ahead and the hallfollow behavior
assumes the robot is in the hall, the script has the robot employ wallfollow
to find the hall, then begin following the hall. The task manager uses the
directional information stored in the database to determine which wall of
the foyer to follow. In the other condition the robot is already in a hall. Since
the robot is not guaranteed to be facing the centerline of the hall (ANBs have
no knowledge of what was done prior to their instantiation except via global
variables), the sub-script turns it to line itself up with the desired hall.

switch(hall)
case not-facing-hall:
//initialization phase
if starting in a FOYER