Page 121 - Dynamic Vision for Perception and Control of Motion

3.4 Behavioral Capabilities for Locomotion 105

control in an active vision system. By extending these types of explicit representa-
tions to all processes for perception, decision-making, and mission planning as
well as mission performance and monitoring, a very flexible overall system will re-
sult. These aspects have been discussed here to motivate the need for both smooth
parts of mission performance with nice continuity conditions alleviating percep-
tion, and sudden changes in behavior where sticking to the previous mode would
lead to failure (or probably disaster).
Efficient dynamic vision systems have to take advantage of continuity condi-
tions as long as they prevail; however, they always have to watch out for disconti-
nuities in motion, both of the subject’s body and of other object observed, to be
able to adjust readily. For example, a vehicle following the rightmost lane on a
road can be tracked efficiently using a simple motion model. However, when an
obstacle occurs suddenly in this lane, for example, a ball or an animal running onto
the road, there may be a harsh reaction to one side. At this moment, a new motion
phase begins, and it cannot be expected that the filter tuning for optimal tracking
remains the same. So the vision process for tracking (similar to the bouncing ball
example in Section 2.3.2) has two distinctive phases which should be handled in
parallel.

3.4.6.1 Smooth Evolution of a Trajectory
Continuity models and low-pass filtering components can help to easily track
phases of a dynamic process in an environment without special events. Measure-
ment values with high-frequency oscillations are considered due to noise, which
has to be eliminated in the interpretation process. The natural sciences and engi-
neering have compiled a wealth of models for different domains. The methods de-
scribed in this book have proven to be well suited for handling these cases on net-
works of roads.
However, in road traffic environments, continuity is interrupted every now and
then due to initiation of new behavioral components by subjects and maybe by
weather.

3.4.6.2 Sudden Changes and Discontinuities
The optimal settings of parameters for smooth pursuit lead to unsatisfactory track-
ing performance in cases of sudden changes. The onset of a harsh braking maneu-
ver of a car or a sudden turn may lead to loss of tracking or at least to a strong tran-
sient motion estimated, especially so, if delay times in the visual perception
process are large. If the onsets of these discontinuities could be well predicted, a
switch in model or tracking parameters at the right time would yield much better
results. The example of a bouncing ball has already been mentioned.
In road traffic, the compulsory introduction of the braking (stop) lights serves
the same purpose of indicating that there is a sudden change in the underlying be-
havioral mode (deceleration). Braking lights have to be detected by vision for de-
fensive driving; this event has to trigger a new motion model for the car at which it
is observed. The level of braking is not yet indicated by the intensity of the braking
lights. There are some studies under way for the new LED-braking lights to couple