Game developers often need to create one node to sit at the root of a character's CATRig. Uses for this node include:
- As a simple marker for the character's motion in a 3D world, for collision detection and similar purposes. For example, you can move the character from one position to another by moving its root node.
- As the node to which the position of all other parts of the character's rig are relative. This allows you to, for example, separate the motion of the character's arms and legs from the motion of the character itself within its world.
In CAT, this feature is called the motion extraction node.
Creating a Motion Extraction Node
You can create a motion extraction node any time after you have created a CATParent node or loaded a CATRig preset.
Here, for example, is Alien, one of the included CATRigs.
Before creating the motion extraction node
The object under the alien, comprising a triangle and arrow, is its CATParent node.
To create a motion-capture node:
-
Select the CATParent node. - Go to the
Modify panel. - Click Motion Extraction Node.
The arrow at the center of the CATParent appears to grow larger:
After creating the motion extraction node
But this is misleading: Hiding the CATParent's arrow is a larger, separate arrow that represents the motion capture node.
If you select the CATparent node, go to the Display panel, and click Hide Selected, you will still see the large arrow representing the motion extraction node.
Or, if you animate the motion extraction node so that alien moves in its world, you will see both the CATParent's arrow and the motion extraction node's arrow.
Animating the Character
Once you have animated the character, you can see the difference in the two arrows:
- The CATParent's smaller arrow represents Alien's original position in the world coordinate system.
- The larger arrow represents Alien's current position in the world, which is also the origin of Alien's local coordinate system.
And now we can distinguish between two kinds of motion:
- The displacement (in the world coordinate system) between the two arrows represents Alien's motion in the world.
- The displacement (in Alien's local coordinate system) of Alien's legs relative to the motion extraction node.