Page 130 - Dynamic Vision for Perception and Control of Motion

114 4 Application Domains, Missions, and Situations

On ordinary state roads with two-way traffic (Appendix A.2.3) the perceptual
capabilities required are much more demanding. Checking free lanes for passing
has to take oncoming traffic with high speed differences between vehicles and the
type of central lane markings into account. With speeds allowed of up to 100 km/h
in each direction, relative speed can be close to 60 m/s (or 2.4 m per video cycle of
40 ms). A 4-second passing maneuver thus requires about 250 m look-ahead range,
way beyond what is found in most of today’s vision systems. With the resolution
required for object recognition and the perturbation level in pitch due to nonflat
ground, inertial stabilization of gaze direction seems mandatory.
These types of roads may be much less well kept. Lane markings may be re-
duced to a central line indicating by its type whether passing is allowed (dashed
line) or not (solid line). To the sides of the road, there may be potholes to be
avoided; sometimes these may be found even on the road itself.
On all of these types of road, for short periods after (re-) construction there may
be no lane markings at all. In these cases, vehicles and drivers have to orient them-
selves according to road width and to the distance from “their” side of the sealed
surface. “Migrating construction sites” like for lane marking may be present and
have to be dealt with properly. The same is true for maintenance work or for grass
cutting in the summer.
Unmarked country roads (Appendix A.2.4) are usually narrow, and oncoming
traffic may require slowing down and touching the road shoulders with their outer
wheels. The road surface may not be well kept, with patches of dirt and high-
spatial frequency surface perturbations. The most demanding item, however, may
be the many different kinds of subjects on the road: People and children walking,
running and bicycling, carrying different types of loads or guarding animals. Wild
animals range from hares to deer (even moose in northern countries) and birds
feeding on cadavers.
On unsealed roads (Appendix A.2.5) where speed driven is much slower, usu-
ally, in addition to the items mentioned above, the vertical surface structure be-
comes of increasing interest due to its unstable nature. Tracks impressed into the
surface by heavily loaded vehicles can easily develop, and the likelihood of pot-
holes (even large ones into which wheels of usual size will fit) requires stereovi-
sion for recognition, probably with sequential view fixation on especially interest-
ing areas.
Driving cross-country, tracks (Appendix A.2.6) can alleviate the task in that
they show where the ground is sufficiently solid to support a vehicle. However,
due to non-homogeneous ground properties, vertical curvature profiles of high spa-
tial frequency may have developed and have to be recognized to adjust speed so
that the vehicle is not bounced around losing ground contact. After a period of rain
when the surface tends to be softer than usual, it has to be checked whether the
tracks are not so deep that the vehicle touches the ground with its body when the
wheels sink into the track. Especially, tracks filled with water pose a difficult chal-
lenge for decision-making.
In Appendix A.2.7, all infrastructure items for all types of roads are collected to
show the gamut of figures and objects which a powerful vision system for traffic
application should be able to recognize. Some of these are, of course, specific to
certain regions of the world (or countries). There have to be corresponding data