Page 363 - Introduction to AI Robotics

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if hall-not-found 9 Topological Path Planning
wallfollow until find the hall
else
if not facing hall
turn to face hall
else starting in a HALL
if not facing hall
turn to face hall
case facing-hall:
//nominal activity phase
hallfollow until next gateway

The navigate-hall ANB terminates when the next expected gateway
(the next node in the path) is found. There are three behaviors which look
for gateways. hallwatch looks for the ultrasonic signature of a hall in the
expected direction; foyerwatch similarly looks for foyers, and the robot
uses vision through the confirm-door behavior to detect the landmark as-
sociated with the room. These behaviors run concurrently with the nominal
behaviors.
The navigate-foyer ANB is used to move the robot between two foy-
ers. It assumes that two foyers’ nodes connected are a connvenient repre-
sentation of a single large foyer with entries from different directions (i.e.,
multiple gateways into the foyer). The script moves the robot n feet into the
first foyer in the direction of the second foyer. This gets the robot away from
potentially confusing ultrasonic signatures. Then the task manager deter-
mines which side of the foyer to wall-follow until the next expected gateway
is detected. There is no case statement in the pseudocode since the sequence
of activities is fixed.

//step 1
move-to-goal(n, dir) in direction of next foyer
//step 2
wallfollow until next gateway is detected

9.5.3 Lessons learned

The CSM team did not place at the AAAI competition; the robot suffered a
series of hardware failures, causing both the power supply and the sonars to