Skeletons and IK

7

Skeletons and Inverse Kinematics

In This Section:

• Drawing a Skeleton with Pivots or Joints 238
• Introduction to Inverse Kinematics 244
• Turning Skeletons On and Off 265
• Copying and Pasting Skeletal Animation and Attributes 267
• Creating and Setting Joint Information 272
• Adding IK Handles to Skeletons 284
• Picking IK Handles 293
• Turning IK Handle Display On and Off 297
• Animating and Rendering Multi-chain IK 299
• Defining a Rest Pose for IK Skeletons 305
• Returning Joints and IK Skeletons to a Rest Pose 307
• Creating a New Constraint Object 310
• Constraining An Object to Another Object 316
• Turning Constraint Display On and Off 329
• Deleting Constraints 330

Drawing a Skeleton with Pivots or Joints

This feature is available in Alias AutoStudio and PowerAnimator and is a purchasable Advanced Animation for Studio option.

Draw skeleton creates a skeleton by defining pivot point or joint positions.

Overview

To use the Draw skeleton tool, select it from the Objects menu, or click its icon.

As you create each joint, a DAG node is added to the Scene Block Diagram (SBD) and a bone is drawn in the modeling windows connecting this joint to the previous joint.

Skeleton Terms

• bone -the connection between each joint (rotation pivot point) in the skeleton. The bone is a purely visual thing, not a DAG object.

• joint, or joint node - a DAG node that is acting as a joint at the end of a bone.

• skeleton - a hierarchical group of bones and joints.

Creating Joint Nodes

A joint node is a DAG node that is marked as a joint. You can see it in the SBD window, where its DAG node has a joint icon.

See Windows > Edit > Skeletons on page 272 for details.

You can also turn existing DAG nodes into joint nodes, or make joint nodes regular DAG nodes by toggling their joint state in the skeleton editor.

Each time you click in the modeling window when using Draw skeleton, a new joint node that is a child of the active joint node is created, and a bone is drawn between the two joints.

You can also create a new joint DAG node by entering the pivot position on the keyboard.

Each time you create a joint DAG node in this way, the pivot position of the joint DAG node is placed where you last clicked in the window.

Using Bones

Bones are drawn between joint nodes and their nearest ancestor joint node by connecting the rotation pivot points of the two nodes. You can change the bone shape (see Object Display > Line style -) or turn off the display of the bones completely (see DisplayTgls > Object Toggles > Skeletons -).

The actual size of a 3D bone is defined by the distance between pivot points. The larger end of the bone shows the location of the rotation pivot point for the joint DAG node above the bone - the smaller end of the bone points to the rotation pivot point for the joint DAG node below the bone. Because the bone is defined by the pivot points, you can use Xform > Local > Set pivot to change the length of a bone.

You can create a chain of joints by clicking several times in an application window. If you want to create a hierarchy interactively, use the Shift key with one of the four arrow keys on the keypad to move around the joint node hierarchy.

Creating a simple spine chain

Bone chains are not limited to living creatures - a desk lamp is a simple bone chain. Using a chain of bones, you can easily create a lamp by clicking and forming sections from the base of the lamp to the shade.

Creating a human-like character

The default DAG node names have been replaced by more meaningful names for the purpose of these examples.

I. Draw the right leg:

1

Select Objects > Draw skeleton.

2

Click to define the position of the pelvis, the right hip, the right knee, the right ankle, and finally the right toe.

II. Draw the left leg:

If you keep clicking now, you'll keep adding joints to the end of the right toe.

To make the left leg, you want the next joint DAG node you create to be a child of the pelvis node.

3

Use the Shift -Up arrow combination to move up the hierarchy until the pelvis is active. You can do this in either the SBD or modeling window.

You can also create the left leg by using Edit > Mirror. (See Basic Tools in Alias.)

4

Click to define the position of the left hip, knee, ankle, and toe as you did with the right leg.

III. Draw the spine and the head:

5

Use Shift-Up arrow to move back up the hierarchy to the pelvis and draw the spine, neck, and head.

IV. Draw the right arm:

6

Use Shift-Up arrow to move back up the hierarchy to the collarbone, and draw the right arm.

V. Draw the left arm:

7

Use Shift-Up arrow to move back up the hierarchy to the collarbone, and draw the left arm.

For more information about skeletons, see Windows > Edit > Skeletons on page 272.

8

You now have the finished skeleton.