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# What is inverse kinematics?

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Learn more about the process and workflow of IK animation.

You can create the illusion of life by using the skeleton and inverse kinematics animation tools in Alias. The essence of character animation is timing and motion.

Build a skeleton by creating and editing joints and bones. After you’ve created all the joints and bones that make up a skeleton for your character, you’ll want to move the skeleton around and put it in various poses.

There are two basic ways to pose a joint chain: forward kinematics and inverse kinematics.

With forward kinematics, when you pose a joint chain you have a specify the rotations of each joint individually, starting from the parent joint on down to all the joints below.

With inverse kinematics, when you pose a joint chain all you have to do is tell the lowest joint chain’s hierarchy where you want it to be, and all the joints above it will rotate automatically. Inverse kinematics offers a very intuitive way to pose a joint chain because it enables goal-directed posing. When you reach for an object, you don’t think about how you are going to rotate your shoulder, your elbow, and so on. You just think about where the object is that you want to reach, and your body automatically does the rest. That’s how inverse kinematics works, too.

To pose a joint chain with inverse kinematics you need to add some special tools to a skeleton. These tools are called inverse kinematics (IK) handles. An IK handle enables you to pose a joint chain intuitively.

An IK handle begins at a joint chain’s parent joint and can end at any joint below the parent joint. For example, for each leg you could create an IK handle that controls the joint chain beginning at the hip joint and ending at the ankle joint.

You can select the IK handle where it ends at the ankle joint and move the chain with it in the same way that you would think about moving your own ankle.

In addition to posing a skeleton, IK handles also play an important role in the animation of the skeleton. The movement of a chain between the keyframes of an animation is also automatically solved by the chains IK handles.

IK handles figures out how to rotate and move all the joints in the chain for you by applying an inverse kinematics solver. The IK solver is the motor intelligence behind and IK handle.

You can animate a skeleton, but such an animation would show only the timing and motion of a character lacking form and shape. The next step is to bind the character’s model to the character’s skeleton so that the skeleton can control the model’s actions.

Use Animation > IK > New Skeleton to create the skeleton, then Animation > IK > Add IK Handle, Animation > Tools > Create Constraint, and Animation > Keyframe > Set Keyframe or Animation > Keyframe > Auto Keyframe to animate your character in its rotation scale and translation parameters.

Create hierarchical geometry for the character independently from the animation and use Animation > Editors > Skeletons to turn DAG nodes in the hierarchy into joint DAG nodes. Then use Animation > Edit > Overlay Skeleton to overlay the corresponding joint nodes in the model.