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Chapter 4. Simulating Visual Attention for Crowds
putation is done with the different activation time values for the three sets of joints (eyes,
head and torso). As depicted in Figure 4.3, we thus obtain a slight delay in the movement
initiation between these three sets of joints.
Temporal propagation fp(t)
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Frames
Figure 4.3: Desynchronization between the eyes, head, and torso. The eyes start moving before
the head and satisfy the constraint first. The head and cervicals start moving and satisfy the
constraint before the remainder of the spine.
Our final movement therefore allows the eyes to converge on the interest point and then
partially re-center with respect to the head as the remainder of the joints move to satisfy the
constraint. Indeed, they only partially re-center as a whole portion of the rotation is done
by the eyes only. In our examples, most characters are in movement and the majority of
the gaze constraints are associated to other characters in movement. These constraints are
thus dynamic. We therefore recompute the displacement map to satisfy the constraint at each
timestep. We can assume that the constraint’s position from one frame to the next does not
change much. We therefore recompute the rotation to be done at each frame but maintain
the total contribution fP (t)ci to apply which we calculated before the initiation of the gaze
motion. However, we reset the contributions to 0 if the gaze constraint changes, i.e., if it
is associated to another entity situated elsewhere in the scene. More specifically, this is the
case when the current constraint location is farther than a pre-determined threshold from the
constraint location at the previous frame. The newly calculated rotations to be performed
by the joints to attain the new constraint’s position are then distributed over the appropriate
number of frames.
4.5 Results
We used our framework to create some examples of the possibilities of our method. The motion
clips for our examples have been sampled at 30 fps. All the animations were generated
on an Intel Core 2 Duo 3.0 GHz, 2GB RAM, NVidia GeForce 8800 GT.
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