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6.3 Designing a Sensor Suite
robot had to know where the camera was turned relative to the robot’s inter-
nal frame of reference in order to correctly transform the location of a white
line in image coordinates to a steering direction. This meant the information
needed for follow-path had both proprioceptive and exteroceptive com-
ponents, making the perception somewhat exproprioceptive. (If the robot
was extracting the pose of its camera from exteroception, it would be clearly
exproprioceptive.)
Due to a programming error, the follow-path behavior incorrectly assumed
that the exteroceptive camera data had been transformed by the propriocep-
tive shaft encoder data from the panning mast into exproprioceptive data.
The robot needed the exproprioception to determine where it should move
next: turn to follow the path in camera coordinates, plus the compensation
for the current camera pan angle. The programming error resulted in the
robot acting as if the camera was aligned with the center of the robot at all
times. But the camera might be turned slightly to maintain the view of both
lines of the path through the pan-camera behavior. The resulting naviga-
tional command might be to turn, but too little to make a difference, or even
to turn the wrong way. This subtle error surfaced as the robot went around
hair pin turns, causing the robot to go consistently out of bounds.

6.3.1 Attributes of a sensor
As can be seen by the above example, robots may have dead reckoning capa-
bilities, but will always have some type of exteroceptive sensor. Otherwise,
the robot cannot be considered reactive: there would be no stimulus from
the world to generate a reaction. The set of sensors for a particular robot is
SENSOR SUITE called a sensor suite. Following Sensors for Mobile Robots, 52 in order to con-
struct a sensor suite, the following attributes should be considered for each
sensor:
1. Field of view and range. Every exteroceptive sensor has a region of
space that it is intended to cover. The width of that region are specified by
the sensor’s field of view, often abbreviated as FOV. The field of view is usu-
ally expressed in degrees; the number of degrees covered vertically may be
different from the number of degrees covered horizontally. Field of view is
frequently used in photography, where different lenses capture different size

and shape areas. A wide angle lens will often cover up to 70 , while a “reg-

ular” lens may only have a field of view around 27 . The distance that the
field extends is called the range.
FIELD OF VIEW (FOV) The field of view (FOV) can be thought of in terms of egocentric spherical