Character Rigging

Ever wonder how characters from video games and other 3d animations are made to move around, and how their movements are getting more and more realistic with each new generation of movies and games?

One of the key components to making this happen is something called rigging, also known as skeletal animation. This is where a technical artist sets up a 3d model of a character or other object so that it can move and be moved. The animator makes the model jump and dance and swordfight and run, but this is possible because of the setup done by the technical artist.

Here is a demo reel made by my brother Dave, a technical artist and character rigger. The beginning clips show some examples of the various types of work he has done, while the second portion of the reel goes through some characters he has created for a new game as he explains the rigging available on each 3d model. See the explanation below for what some of the terms he is using mean.

Source: Dave Cohen's Rigging Showreel

And now a brief explanation of what some of these terms mean. And how this is done.

Suppose you want to animate a human character for a game. This character needs to be able to walk along, to jump, and to have facial expressions.

Some of the movements provided for the animator are set up to support something known as Forward Kinematics, or FK for short. This describes the computations necessary to make sure that, for example, when you move the upper leg of the 3d model forward, the knee, lower leg, and foot move along with it. The position of a particular piece of the model is calculated based on the angles of the joints and the length of the "bones" that connect it to the rest of the model.

FK is also typically used to tilt and turn the head, open and close the jaw, open and close eyelids, etc. With FK, you manipulate joints and the system figures out how the model moves accordingly.

Another technique used for rigging is called Inverse Kinematics, or IK for short. This describes the computations necessary to set a portion of the model to a particular position and figure out the angles and positions of the joints accordingly. For example, if you want to make your 3d person walk, you can just move the foot forward to take a step, and IK figures out how the leg joints need to move to make that happen. Additionally, the foot can then remain on the ground while the body moves above it, and IK will figure out how the joints move to make this happen.

Prior to Inverse Kinematics, the animator had to manipulate each joint to put the foot in the proper place using Forward Kinematics to make the 3d person take a step. Worse, they then had to counteranimate the foot to get it to stay on the ground while the rest of the body moved forward. This sometimes resulted in walking characters looking like they were sliding, or made the walking look jittery and unrealistic.

For facial animations, the rigger sets up scripts that do math that calculates how the various components of the face should move or deform to make the mouth move for speech, raise the eyebrows, scrunch the forehead, puff out the cheeks, and whatever other tools the animator will need to make the character speak, show surprise, fear, anger, and other emotions, and do other things like smile and frown.

Comments

[Nik]

That stuff is so cool.

[Jessica]

It blows my mind how few people know what rigging is - most people just think that once the model is done it can just be moved. I'm a character TD, and explaining what I do is always interesting.

Thanks for posting this!