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3D Animation
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Keyframes, Function Curves
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Define parameter values manually at selected points in time (keyframes);
let the software interpolate the values at all remaining times ("inbetweening",
"tweening")
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Use: translation, rotation, scaling, object parameters, light parameters,
material parameters, ...
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Control of ease-in/ease-out through spline-like curves (Demo: function
curve editors of Cinema 4D and Maya)
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Hierarchical Animation
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Represent a complex object as a hierarchy of nodes, which are organized
in parent-child relationships so as to form a tree. A node may possess
geometry or may be used simply as a grouping device. A motion of a node
(e.g., the upper arm) influences all the nodes below it (e.g., the lower
arm, hand, fingers). (Demo in Cinema 4D and Maya)
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Forward Kinematics: To set a pose for keyframe animation, adjust the object
starting with the top-level nodes, working downward.
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Inverse Kinemantics: To set a pose for keyframe animation, pull a final
node ("end effector"); the software has to compute the new positions and
orientations of the nodes. This process may also be used directly for animation:
Animate the "goal" of the end effector. (Demo in Cinema 4D and Maya)
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Rotations cannot be interpolated easily
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Translations and scalings can easily be blended between keyframes, but
rotations cannot, at least if one uses xyz rotation angles ("Euler angles")
to do the blending: Due to the non-commutativity of rotations, the object
does not rotate smoothly. (Demo in Cinema 4D)
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This problem can be overcome with other descriptions of rotations, for
instance unit quaternions.