When a modeller finishes a character, the model looks like a marble sculpture. Before a 3D character model (for example to create 3D configurator) can be passed to the animators, it must be bound to a system of joints and control handles so that the animators can position the model. This process is usually performed by artists known as Character Technical Directors (TDs) or Riggers.
TDs work closely with animators to ensure that all specific technical issues are addressed. Their main task is to take a static 3D mesh and prepare it for animation – a process known as rigging.
Rigging.
A character rig is essentially a digital skeleton bound to the 3D mesh. Like a real skeleton, a rig consists of joints and bones, each of which acts as a handle. In this way, animators can bring the character into the desired position.
A character rig can range from simple and elegant to amazingly complex. A simple setup for simple poses can be set up in hours, while a fully articulated rig for a feature film can take days or weeks before the character is ready for Pixar animations.
Insertion of the skeleton.
Skeleton placement is perhaps the simplest part of the rigging process.
In most cases, the joints should be placed exactly where they are in a real skeleton, with one or two exceptions.
Common Hierarchy: For a rig to function properly, bones and joints must follow a logical hierarchy. When setting up a character`s skeleton, the first joint that is placed is called the root joint. Each subsequent joint is connected to the root either directly or indirectly via another joint.
Forward Kinematics: Forward Kinematics is one of two basic methods to calculate the joint movement of a fully rigged character. When using forward kinematics bracings, a given connection can only affect parts of the skeleton below in the connection hierarchy.
For example, the rotation of a character`s shoulder affects the position of the elbow, wrist, and hand. In Forward Kinematics animation, the artist typically has to adjust the rotation and position of each joint individually to achieve a desired position. To do this, the animator must work through the joint hierarchy sequentially. The end position of an end joint is calculated as a function of the joint angles of each joint above it in the hierarchy.
Inverse Kinematics.
Inverse Kinematics is the reverse process of Forward Kinematics and is often used as an efficient solution for rigging a character`s arms and legs. In an Inverse Kinematic rig, the final joint is placed directly by the animator, while the upper joints in the hierarchy are automatically interpolated by the software.
Inverse Kinematics is best used when the animation requires an end connection that needs to be placed very accurately. A good example is a character who has to climb a ladder.
Since a character`s hands and feet can be placed directly on the ladder rungs instead of the animator having to adjust his position in an articulated manner, an Inverse Kinematics Rigg would make the animation process much more efficient. A disadvantage is that the Inverse Kinematics uses software interpolation. This means that a lot of cleanup work has to be done to complete the capture.
Degrees of freedom and limitations.
When rigging, keep in mind that in the real world, joints like elbows are limited to a single degree of freedom, i. e. they can only bend along one axis. Likewise, a human neck cannot be rotated 360 degrees.
In order to avoid unrealistic animations, it is adviseable to set up common constraints when building the rig.
Squash and Stretch.
Other considerations to be considered are whether the rig supports squash and stretching or whether the character is limited to realistic movements.
Squash and stretching is an important principle in cartoons, but usually doesn`t look right in realistic film or VFX work. If the rig is to maintain realistic proportions, restrictions must be set to fix the position of each joint in relation to the rest of the rig.
A character`s facial rigging is usually completely separate from the main controls. It is inefficient and incredibly difficult to create a satisfactory facial rig with a traditional joint/bone structure, so morph targets are usually considered a more effective solutions.
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