Rigging and Anatomy
Making your characters move convincingly

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Understanding anatomy is essential when you are rigging a character. Everything from where you place the joints in the character to how you weight them should all take anatomy into consideration.

Sometimes in the CG world this can be a challenging process. More often than not there is no real life counterpart to the character that you are working on. So how should it move? One of the fun things about being a Creature TD is bringing the character to life and figuring all of that out. After reading this, you should have a general idea of the process.

Once your character is modeled, the outside anatomical structure is fairly obvious. It's really just a matter of getting in there and making it move. One of the first things you do when rigging a character is make your joints. Proper joint placement is essential. You need to figure out the underlying skeleton of the character you're working with. How does it move? What kind of joint would that be, a hinge, or a ball joint? Where should the joint go? These are all questions you should ask yourself when figuring out how to place your joints.

You can find a good amount of reference in human and animal anatomy books. Of course, for humans, there's no better reference than yourself. Stand in front of a mirror and move around. Watch your skin as it slides over the muscle and fat. You'd be surprised just how many parts are moving in order for you to do a simple task such as raising your hand in the air.

A good rule of thumb for joint placement is to place the joint right in the middle of where the movement should be. For example, you wouldn't want to place an elbow joint in the middle of the bicep that would obviously not work. Try to place the joint as close to the area as possible where the skin will actually be moving.

You also want to make sure you're placing enough joints in the character for the particular part you wish to have move. For example, I have seen quite a few rigs with only one joint for the shoulder. A closer look at the human anatomy will reveal that just one joint is not nearly sufficient enough. There's the bone that runs along the outer edge from your collar to your shoulder, the clavicle, and then there's the scapula, a large bone in your mid back that runs upward to connect to your shoulder. These two are then weaved together with muscles and tendons that also incorporate the ball joint in your arm. So, just by looking at that, it should immediately become apparent that just one joint will not give you all the movement you need.

Click image for larger view.
I personally prefer a two joint setup for the clavicle, and a three joint setup for the scapula. I connect them together using IK handles. A setup like this gives you more control over the skin when weighting. Instead of one joint, you now have five that can all be weighted to.

This brings me to another good point. When you're making that many joints, you still only need one control for all of them. They should essentially be automated so that when an animator raises the shoulder control the entire system follows accordingly. Things can begin to get tricky as you try to figure out how to connect everything together, so try to plan out how it will all work before you actually make it.

This is just one of many examples of what studying anatomy will reveal when you start rigging a character. The goal is to be accurate, but also to be practical so that an animator can quickly pose the character.

Keep in mind too of how your character was modeled when you're placing joints. Is there a bend in the arm? Is the back hunched over? Are the knees bent or straight? You should make your joints according to how the model was built. Accommodate any slight differences, such as bent knees, by drawing the joint chain at an angle as opposed to straight down.

Complete skeleton (Click for larger view)
When you have finally placed all of your joints and connected them together, they should look like a skeleton of the character. In fact, it may be helpful to actually model the bones associated with each joint, just so you can get a good idea of the anatomical structure of the character you're working with.

It might be a good exercise to help you learn too. In fact, if you're interested in becoming a TD, knowing anatomy will help you in many ways, and it's a big plus on your resume.

You are now ready to finish your rig. Add in your IK handles, your controls, constraints, and anything else you might need to make it move. In my opinion, it is good practice to have a complete working rig before you ever begin skinning. You don't want to start weighting only to find out that something didn't work like you had planned, or that maybe the joints aren't where they're supposed to be. Any changes should be done beforehand.

Once your rig is complete, now is a good time to test it. Spend some time playing with the controls and make sure things are moving like you expect them to. If you find problems, fix them, and move on. Keep in mind the anatomy of the character you’re working on. Does the character move like you want? Is there anything else you think you should add? If you can, try looking at video footage of a similar character moving around. If it's a fantasy creature, try to find animals with similar movements and watch footage of them in action. If you have access to local zoo, go visit and take your camera with you. Try to capture the movements of the animals and use them as reference.

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