Define: 3D Rigging Terminology.

Key 3D Rigging Terms

Joints

Sometimes called bones, you can think of joints for rigging in the same way you think of joints in a human body. They basically work in the same way. Joints are the points of articulation you create to control the model. For instance, if you were to rig a character’s arm you would want to place a joint for the upper arm, another joint for the elbow and another joint for the wrist, which allows the animator to rotate the arm in a realistic way.

Driven Keys

To speed up
To speed up the animation process for the animators, a rigging artist can utilize driven keys when rigging a character. Driven keys allow you to use one control or object to drive multiple different objects and attributes. In the example above we can use a driven key to control the fist position for the hand, with just one single control.

A driven key contains two parts: the driver and the driven. The driver is the object in control of the animation. The driven is the objects and attributes that are being controlled by the driver. Typically for regular keyframes an attribute has values keyed to time in the time slider. For a driven key, the attribute has values keyed to the value of the driving attributes. The driver can be another object, or in the case of the example image above it is a control slider.

Blend Shapes

A blend shape, or morph depending on your 3D application, allows you to change the shape of one object into the shape of another object. When rigging, a common use for blend shapes is to set up poses for facial animation. This might be lip sync poses or more complex expressions like a smile or frown. You can tie all these new poses into the original face mesh and have it operate all on one control slider.
For example, if you want to raise an eyebrow you can model a face pose with one eyebrow raised, connect it to a blend shape and using the slider with a value of 0 to 100 to either raise or lower the eyebrow. This is a great way for the animator to be able to quickly make face poses without having to move individual facial controls around. There are some downsides to using blend shapes for facial poses, because the edit ability can be limited. Riggers often will give the animators both blend shape options and traditional control points to use them in conjunction.
IK(Inverse Kinematics)

FK(Forward Kinematics)

Control Curves

Control curves are created by the rigger to assist the animator in manipulating joints within the rig. Typically a rig consists of many components that need to be manipulated to move the character in the desired pose. This can be very difficult to do without control curves because the animator would need to hide the mesh to see the skeleton within the character and try to determine which joint manipulates the elbow, for example.

Control curves are typically simple NURBS curves placed outside of the character so the animator can easily select the curve to position the character instead of the actual joint.

Constraint

Constraints are very important in both the rigging and animation process. Typically your 3D application will have several options for constraining. Constraints limit an object’s position, rotation and scale based off of the attributes of the parent object. For example, by taking two separate spheres, applying a parent constraint, and then deciding which is the parent and which is the child, you can select just one and the other will follow whatever the parent is doing.

Setting up constraints is a vital step when creating control curves for the rig. For example, you will need to determine the type of affect that a control curve has on an individual joint. Setting up constraints will allow you to do this.

Deformers

There are many different deformers/modifiers depending on your 3D application which can be utilized to enhance your rigs. Deformers are often used among modelers but they are also extremely helpful for riggers as well. Deformers contain algorithms that can move large sections of vertices on a model to produce organic shapes. For example, when rigging a character you can utilize something like a cluster deformer that allows you to manipulate a large section of vertices by using just one single control.

Once created, a cluster can be constrained to a control object. This is great for creating facial controls like cheeks or eyebrows. To learn more about deformers check out this in-depth

Skinning

Skinning is the process of taking the joints or bones of the rig and binding them to the actual 3D mesh. When the joints are bound to the 3D mesh it allows you to move the joints and the mesh will follow. Without skinning the mesh to the joints the joints will have no influence on the actual 3D model.

Weight Painting

Weight painting is a vital step once the skeleton has been created. Even though the bones are put into place, it doesn’t mean the 3D model will be able to deform exactly how you want. When a mesh is bound to the skeleton, the computer doesn’t know how much influence each joint should have over each vertex, so it averages the weight out based on the distance from the joint to the mesh.

Basically painting weights allows you to manually set how much influence a joint has on a particular area of the model and correct the deformations on the 3D mesh. For example, if the leg joint has too much influence on the model it might affect the torso area giving you unrealistic results.





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articulation

4.a joint in an animal
5.a node of a plant, or the space on a stem between two nodes

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Inverse Kinematics

1. a branch of physics that deals with the motion of a body or systemwithout reference to force and mass  in the inverse direction.

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