What is a skeleton in animation?

It is an invisible hierarchy of bones inside a character; moving the bones deforms the attached surface mesh through skinning, so animators pose the simple skeleton rather than every vertex.

Why use quaternions for rotation?

Quaternions interpolate rotations smoothly along the shortest path and avoid gimbal lock, a problem where Euler-angle representations lose a degree of freedom and produce jerky or undefined motion.

Keyframe and Skeletal Animation

Keyframe animation specifies motion at selected times and interpolates between them, and skeletal animation drives a character's surface through an underlying hierarchy of bones.

Find Topic with PaperMindSoonFind papers & topics

Tools & resources

Download slides

Learn & explore

VideoSoon

Definition

Keyframe animation interpolates scene parameters between artist-set key poses, and skeletal animation deforms a character mesh according to the pose of a hierarchical bone structure.

Scope

This topic covers interpolation of positions and orientations including quaternion interpolation of rotations, articulated skeletons and forward kinematics, skinning that binds a mesh to bones, and inverse kinematics that solves for joint angles to meet positional goals.

Core questions

How are smooth in-between frames generated from key poses?
How are rotations interpolated without distortion?
How does a bone hierarchy deform a character's surface?
How are joint angles found to reach a target position?

Key concepts

Keyframe interpolation
Spline and quaternion interpolation
Bone hierarchies
Forward kinematics
Inverse kinematics
Skinning and skin weights

Key theories

Quaternion rotation interpolation: Representing orientations as unit quaternions and interpolating them with spherical linear interpolation yields smooth, shortest-path rotation without the gimbal lock and distortion of interpolating Euler angles.
Forward and inverse kinematics: Forward kinematics computes a character's pose from joint angles down a bone hierarchy, while inverse kinematics solves the harder inverse problem of finding joint angles that place an end effector at a desired location.

Clinical relevance

Keyframe and skeletal animation are the foundation of character animation in film and games, of avatars in virtual and augmented reality, and of articulated motion in robotics and biomechanics visualization.

History

Keyframe systems descend from traditional animation; Shoemake's 1985 quaternion curves solved smooth rotation interpolation, and skinning with inverse kinematics became standard for articulated characters in production pipelines.

Key figures

Ken Shoemake
Rick Parent

Seminal works

shoemake1985
parent2012

Frequently asked questions

What is a skeleton in animation?: It is an invisible hierarchy of bones inside a character; moving the bones deforms the attached surface mesh through skinning, so animators pose the simple skeleton rather than every vertex.
Why use quaternions for rotation?: Quaternions interpolate rotations smoothly along the shortest path and avoid gimbal lock, a problem where Euler-angle representations lose a degree of freedom and produce jerky or undefined motion.