Behavior-Based Indoor Navigation - Ambient Intelligence for Scientific Discovery - page 269

entation. More specifically, the robot needs to recognize several environmental
properties that change the orientation to follow, according to the situation and
the task. The environment can be provided with specific landmarks so that the
robot can easily identify different locations. Instead, we chose to extract environ-
mental characteristics that can be recognized by robot sensors. We think that
it is necessary to assess the level of performance robotic intelligent systems can
reach without limiting the properties of the environment to suit the robots' be-
havior. Therefore, our approach exploits natural landmarks, namely, corridors,
emergency exit panels and doors.

Corridor Identification. Corridors present very strong properties that make
them identifiable. Moreover, most of the oce doors are located at the corri-
dors. Thereby, corridor recognition is an interesting capability for the robot to
consider. Equation (1) shows the single rule applied for corridor identification,
where dist refers to the corridor width measured by left and right sonars.
corridor id ( t )= 1if dist < T hreshold
0else

(1)

To make the corridor identification more robust, instead of just trusting a
single sonar and compass reading, we maintain a belief value of being in each
corridor. For that we use a fixed sized FIFO (First In, First Out) buffer that
contains the results of the corridor identification behavior for the last

BSIZE

(buffer size) readings:

t

Bel ( corridor )= corridor id ( k ) × w k

k =( t−BSIZE )

where w k is an increasing weighting parameter that gives more importance to
the recent values of corridor id . The buffer size determines the delay with which
the new location is identified and, together with the weights, the effect of dis-
turbances on the confidence level.
The maintenance of a belief state of being in a corridor allows us to also detect
transitions from corridors to non-corridor places. These transitions are used to
change the desired compass orientation according to the state or location of
where the robot is. Forcing the robot to enter narrow corridors becomes more
dicult. Specific mechanisms are needed to detect crossroads and change the
desired compass orientation to reach the next goal.

Emergency Exit Panel Identification. Emergency exit panels are interna-
tional, natural landmarks mandatory in every public building that must follow
some shape, color and location standards 2 . As natural landmarks in the environ-
ment, they can be used to implement navigation strategies such as recognition-
triggered response. To extract the panel from the background in the image, a
2 E.g., European “Council Directive 92/58/EEC of 24 June 1992 on the minimum
requirements for the provision of safety and/or health signs at work”. Ocial Journal
L 245 , 26/08/1992 P. 0023-0042.