Page 65 - Dynamic Vision for Perception and Control of Motion

2.2 Objects 49

This difficult task has to be solved in the initialization phase. Within each class
of aspect conditions hypothesized, in addition, good initial estimates of the relevant
state variables and parameters for recursive iteration have to be inferred from the
relative distribution of features. Figure 2.16 shows the features for a typical car; for
each vehicle class shown at the top, the lower part has special content.

(horse) Aspect graph
Cart Vehicle Truck
Aspect
Vehi- hypothesis
Typical features instantiated
Van
cle for this
Motorcycle aspect condition View from
rear left
types bicycle Right rear group
Straight from Left front group of lights
front of lights
Left front
Right rear
Single wheel wheel
Front Car Front Elliptical
right left central blob License plate
vehicle
Straight Straight Dark tire below Dark area
right left body line Left rear underneath car
aspect wheel
Left rear
Rear Elliptical group of lights
tree right Rear central blob
Straight left Dark tire below body
behind
Figure 2.16. Vehicle types, aspect conditions, and feature distributions for recognition
and classification of vehicles in road scenes
In Figure 2.17, a sequence of appearances of a car is shown driving in simula-
tion on an oval course. The car is tracked from some distance by a stationary cam-
era with gaze control that keeps the car always in the center of the image; this is
called fixation-type vision and is assumed to function ideally in this simulation,
i.e., without any error).
The figure shows but a few snapshots of a steadily moving vehicle with sharp
edges in simulation. The actual aspect conditions are computed according to a mo-
tion model and graphically displayed on a screen, in front of which a camera ob-
serves the motion process. To be able to associate the actual image interpretation
with the results of previous measurements, a motion model is necessary in the
analysis process also, constraining the actual motion in 3-D; in simulation, of
course, the generic dynamical model is the same as in simulation. However, the ac-
tual control input is unknown and has to be reconstructed from the trajectory
driven and observed (see Section 14.6.1).

2.2.5 Representation of Motion
The laws and characteristic parameters describing motion behavior of an object or
a subject along the fourth dimension, time, are the equivalent to object shape repre-
sentations in 3-D space. At first glance, it might seem that pixel position in the im-
age plane does not depend on the actual speed components in space but only on the
actual position. For one time this is true; however, since one wants to understand 3-
D motion in a temporally deeper fashion, there are at least two points requiring
modeling of temporal aspects: