3D Rigging Terms

Rigged Models

Most commonly, 3D characters are rigged before they are animated because if a character model doesn’t have a rig, they can’t be deformed and moved around. Having rigged models or 3d characters are the standard step for a modeler to be able to make a specific scene or scenario. Although the rigging process can become very technical and seem overwhelming at times. After a little practice will help you create great rigged models or rigs in no time.

The process of creating a skeleton for a 3D model so it can move is called 3D rigging. Rigging a character is a very time-consuming process. It needs precision, creativity, artistry, and an eye for detail. Character riggers are responsible for using computer programs and software that aids the rigged models forming the skeletons by creating a series of bones that deform and animate specific parts of the 3D character.

Rigging

A character rig is essentially a digital skeleton bound to the 3D mesh. Like a real skeleton, a rig is made up of joints and bones, each of which acts as a “handle” that animators can use to bend the character into the desired pose.

A character rig can range from simple and elegant to staggeringly complex. A basic setup for simple posing can be built in a few hours, while a fully articulated rig for a feature film might require days or weeks before the character is ready for Pixar-level animation.

Skeleton Placement

Joints: Skeleton placement is the easiest part of the rigging process. Joints or sometimes called bones can be treated the same way as the human skeletal system in rigging. Joints are the points where we can create controls to the model. An example is when you 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, helps the 3d animator to rotate the arm in a realistic fashion.

In order for rigged models to work properly, a logical hierarchy must be followed. When setting up a model’s skeleton, the root joint must be placed first. The rest of the joints will be connected directly, or indirectly to the root or through another joint.

Forward Kinematics is one of the two basic ways to calculate the joint movement of fully rigged models is called Forward Kinematics or FK. Using FK rigging at any given joint can only affect parts of the skeleton that fall below it on the joint hierarchy. An example is rotating a character’s shoulder changes the position of the elbow, wrist, and hand. Animating with forward kinematics, an artist will need to set the rotation and positioning of each individual joint in order to achieve the desired pose. The animator will work through the joint hierarchy which is from the root, spine, shoulder, elbow etc.

inverse kinematicsInverse Kinematics is the reverse rigging process from forward kinematics. It is often used as an efficient solution for rigging a character's arms and legs. In IK rigging process the terminating joint is directly placed by the animator, while the joints above it on the hierarchy are automatically interpolated by a software.
IK is most appropriate when the animation calls for a terminating joint to be placed very precisely; a good example is a character climbing a ladder. Since the model's feet and hands can be placed directly on the ladder's rungs rather than the 3d artist having to adjust their position joint-by-joint, in inverse kinematics rig would make the animation process far more effective. Since IK animation uses software interpolation, it's a drawback that there's often quite a bit of cleanup work needed to finish this step.

Constraints

Keep in mind that when rigging, joints like the elbows and knees are limited to a single degree of freedom in the real world. This means that they can only bend along one axis. Obviously, a human neck cannot rotate a full 360 degrees. Setting up join constraints will greatly help prevent unrealistic animation. It is a good idea to set up joint constraints when you are building your rig.

Facial Rigging

rigged modelsBefore starting your rigging project, you need to identify certain criteria and have a clear visualization on how your rigged models’ behavior and functions  The models you are rigging and its topology are critical to how well the character will move. It is important that the topology is not only clean but that the edge loops follow natural muscle lines. If this is done accordingly, the facial movements will result in a much more realistic way.

A character’s facial rig is often separate from the main motion controls. It’s inefficient and incredibly difficult to create a satisfactory facial rig using a traditional joint/bone structure, so morph targets (or blend shapes) are usually seen as a more effective solution.

Character rigging is a very tedious task from all the previous steps. To successfully create fully rigged models, an animator must be able to create a smooth and ready to use rigged models for game development or any type of productions that a 3d model is needed.

Facial rigging is a much difficult task to perform as an animator thus this topic will need to be discussed further in the next blogs coming soon.

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