thesis - Computer Graphics Group - Charles University - Univerzita ...

9.2. DEMO APPLICATION 117
Scene scenes/animation with pointing arm.txt demonstrates how the animation of a human
figure can be edited so that the figure’s right arm would point in the specified direction. This
is implemented by attaching a MotorJoint to the figure’s hand and imposing a bounded equality
constraint that constrains the hand to occupy the specified world space position corresponding
to the point the hand should point at.
Another example, implemented by scenes/animation with basket.txt, attaches a basket
to the figure’s right hand and lets the animation system adapt the motion. The basket is represented
by a general rigid body with mass properties and is attached to the figure’s hand by
a joint that simulates the friction between the basket and the hand. The figure’s controller is
adjusted so that the right arm is made more stiff (animation constraints are less soft).
Finally, scenes/animation with umbrella.txt demonstrates how the animation can be
mapped to a figure that holds an umbrella in its right hand. Please notice that the umbrella
is always held upright, regardless of the figure posture (ie. even when the figure bows, for example),
that the umbrella is held in front of the head and the hand is always correctly oriented
with respect to the umbrella handle. This is implemented by three additional constraints. An
umbrella is created as a rigid body attached to the figure’s hand by an appropriate anchor joint
that enforces the proper umbrella versus hand orientation. Another constraint pulls the figure’s
hand in front of its head and the third constraint demands that the umbrella is held upright.
9.2.5 Retargetting and Combining Animations
The problem of transferring animations that fit a certain figure to another figure (motion retargetting)
and the problem of combining motion segments (so that the transition between the
segments would be smooth and realistic) are often hard to solve on the kinematics level. With
the help of dynamics, the problems can be handled much easily. The reason for this to work is
the fact, that the kinematic data (controller inputs) that might be inconsistent with the dynamics
of the animated figure are automatically “corrected” by the dynamics system, if the figure
controllers are programmed not to follow the (inconsistent) inputs exactly.
Scene scenes/fat man animation.txt retargets the animation of the default figure to a fat
figure with very different body proportions — limbs are much shorter than those of the original
figure and the torso is bigger and hunched. When we were preparing this test, we modified the
original skeleton, the collision geometries and their mass properties to represent the fat body,
but did not have to modify the animation data. The rest of the work is due to the rigid body
dynamics.
Scene scenes/combined animation.txt presents how two animation sequences can be combined.
The animation controller blends (interpolates) inputs from the two animation sequences
while making a transition from one animation to the other one and the dynamics system “corrects”
the blended animation if it is inconsistent with the dynamics of the figure. Standard linear
interpolation is used to interpolate the translational data and the spherical linear interpolation
to interpolate the rotational data.
9.2.6 Optical Motion Capture To Skeletal Motion
Motion capture is used to capture the motion of actors so that it could be replayed on the
computer. An actor, equipped with motion capture sensors, performs the desired motion that
is captured by the motion capture device. The captured data are then analysed and mapped
to skeletal motion so that it could be replayed using kinematics or dynamics based techniques,
[19]. In the case of optical motion capture, the motion capture device provides the trajectories