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3.3 Perceptual Capabilities 65

3.3.2 Vision for Ground Vehicles

Similar to the differences between insect and vertebrate vision systems in the bio-
logical realm, two classes of technical vision systems can also be found for ground
vehicles. The more primitive and simple ones have the sensory elements directly
mounted on the body. Vertebrate vision quickly moves the eyes (with very little in-
ertia by themselves) relative to the body, allowing much faster gaze pointing con-
trol independent of body motion.
The performance levels achievable with vision systems depend very much on the
field of view (f.o.v.) available, the angular resolution within the f.o.v., and the ca-
pability of pointing the f.o.v. in certain directions. Figure 3.2 gives a summary of
the most important performance parameters of a vision system. Data and knowl-
edge processing capabilities available for real-time analysis are the additional im-
portant factors determining the performance level in visual perception.

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- Light sensitivity, dynamic range (up to 10 )
-Shutter control
- Black & white, Simultaneous field of view
- Color
Angular resolution
per pixel
Fixed focus or
- Number
of pixels on chip zoom lense
- Frame rates possible Potential
- Number of chips for color pointing directions
Single camera or arrangement of a diverse set of cameras for
stereovision, multifocal imaging, and various light sensitivities.

Figure 3.2. Performance parameters for vision systems

Cameras mounted directly on a vehicle body are subjected to any motion of the
entire vehicle; they can be turned towards an object of interest only by turning the
vehicle body. Note that with typical “Ackermann”-type steering of ground vehicles
(front wheels on the tips of the front axle can be turned around an almost vertical
axis), the vehicle cannot change viewing direction when stopped, and only in a
very restricted manner otherwise. In AI-literature, this is called a nonholonomic
constraint.
Resolution within the field of view is homogeneous for most vision sensors.
This is not a good match to the problem at hand, where looking almost parallel to a
planar surface from an observation point at small elevation above the surface
means that distance on the ground in the real world changes with the image row
from the bottom to the horizon. Non-homogeneous image sensors have been re-
searched [e.g., Debusschere et al. 1990] but have not found wider application yet. Us-
ing two cameras with different focal lengths and almost parallel optical axes has
also been studied [Dickmanns, Mysliwetz 1992]; the results have led to the MarVEye–
concept to be discussed in Chapter 12.