Doc:Tutorials/Animation/Armatures/BSoD/Tracking
From BlenderWiki
[edit] Understanding Target Tracking
In many rigs, it's necessary to have one bone target another, free-floating bone. This relationship is the critical component that makes the last three spine rigs work, and is the foundation for the arm and both leg rigs shown here. Suffice it to say, this section is important, even if it is a little boring.
In this section we're going to learn about the behavioral difference of the Track To and IK constraints. Both of these cause the assigned bone to point to a target, but as that target moves the bone farther and farther away from it's original orientation, the bone's rotation around it's local Y axis takes on a life of it's own. We need to understand how these two constraints behave so we can try to tame them, and bend them to our will!
[edit] Track To Constraint
The Track To constraint does two things:
- It directs your object to point at a target with one of it's axes
- It also forces the bone to stay 'right-side up'.
The direction that is considered 'up' is the global +Z direction.
The constraint forces the bone to remain right-side up, so it will flip over if the target passes directly above or below it. You pick which side is the 'right' side, but it has to be one of the three positive axes of the effected object. See track to constraint.
[edit] IK Constraint
The IK constraint can be used on a single bone to do the same thing as the track to constraint, but the IK constraint has a different behavior. It doesn't base part of it's orientation on the global Z axis. Instead, it keeps the rotations based on the orientation of it's rest position, relative to its parent. This is critical to the proper functioning of an IK chain. Imagine the implications if you use IK on the spine of your character, a spine with bones pointing straight up!. If IK worked like Track To does, your character's torso would be spinning in circles all the time. You could never have a character reach toward the sky or the ground, you couldn't allow your bipeds to stand up straight, arms at the sides. Character animation would be virtually impossible.
[edit] Making the Comparison
 Track To |  IK Solver |
In these images, the pits in the spheres represent rotational poles. These are the locations where all possible Y axis rotations come to a single point. Track To has two poles, and the IK solver only has one.
Keep in mind that not only are the location and number of the poles different, but they are also based on different coordinate systems.
Wavez 19:29, 1 May 2007 (CEST)
Redirects to fix
- BSoD/Introduction to Rigging/Arm Rigs → Doc:Tutorials/Animation/Armatures/BSoD/Arm Rigs
- BSoD/Introduction to Rigging/Constraints and Axis Locks → Doc:Tutorials/Animation/Armatures/BSoD/Constraints and Axis Locks
- BSoD/Introduction to Rigging/Some Beginner Rigs → Doc:Tutorials/Animation/Armatures/BSoD/Some Beginner Rigs
- Blender Summer of Documentation → BSoD
- Manual/Manual → Manual
Contents |
