3. Select the LRA for “joint3.”

4. Highlight rotate -r -os 180 0 0; in the Script Editor.

5. Press Enter. The LRA will flip 180 degrees and the joints will have a similar orientation.

[Figures 7 & 8] Component mode (top). The Attribute Editor in Maya (bottom), with the Transform Attributes and Joint tabs expanded.

Interactively Altering an LRA
When you have the LRA selected for a joint, you can interactively alter the rotation axis with the standard Rotation Manipulator tool. When you change the LRA with this method, you can look in the Attribute Editor to see the results. Since you’re not actually rotating the joint, you won’t see a numerical change in the Channel Box.

1. Select an LRA on one of the joints and then open the Attribute Editor.

2. Expand the Transform Attributes and Joint tabs (see Figure 8).

When you alter the rotation of an LRA on the selected joint using a script, you will see that the rotate axis and the joint orient change values exactly opposite each other in order to keep the joint from rotating. Manipulating the LRA interactively changes those values in the same fashion, but without the accuracy. If your intention is to flip an axis a set amount, using a script is the best way to do so.

If you’re making changes interactively, be careful not to alter the alignment of the axis that’s pointing down the bone—most likely the X-axis. If the X-axis is out of alignment, then doing a simple rotation of the joint in Z or Y will change values on all three axes. This is problematic for a character because the rotation of the joints should be on their true axis. It’s very difficult to animate a character when you must adjust three axes to achieve a rotation that should be handled by just one axis.

Manipulating the Location of Joints
There are several ways to manipulate the location of your joints after you have created them. When you create a joint chain, you build a hierarchy of joints; therefore, when you translate one of the parent joints, the children will be affected. Each of the following methods has certain advantages and disadvantages:

Translating joints. If you translate a joint that is a child of another joint, you will alter the relationship of its local rotation axis to its parent. However, if you translate along the direction of the bone (most likely in local X), you will not affect this relationship. The parent will be connected to the child by a bone, but it will no longer point in a direction down that bone. If a joint’s position has been modified in any direction other than along the bone’s axis, you may have to reorient the local rotation axis.

Scaling the bone length. If you choose to scale the joint, you’ll be adding or subtracting the scale values to the joint.

Rotating joints. If you choose to rotate the joint, you’ll be adding or subtracting the rotation values to the joint.

Rotating the joint orient. This method leaves the rotation values for the joint as they are and rotates the relative direction of the joint wherever you direct it. This, in combination with translating the joint along its bone length (again this is most likely the X-axis), is the best method with which to place your joints once they have been created. We’ll elaborate on this below in the sidebar entitled “Getting a Joint to Hit the Mark.”

Translate the joint’s pivot point. Translating the joint’s pivot point is distinctly different from the other methods, in that when you use it, the joint’s children are not affected by the translation. For example, you can make an adjustment to your knee joint and leave the joints of the foot in place. If you’re happy with your foot joint placement, using one, two, or more of the methods listed previously can be an arduous process. Your goal when you start the skinning process is to have translation values in only one channel for all of your joints in a chain, and again, it is usually “x.”