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[edit] Track To Constraint
Mode: Object Mode and Pose Mode
Panel: Object Context → Constraints
Hotkey: F7
[edit] Description
The Track To constraint applies rotations to the object, so that it always points a local “To” axis towards the target object, with another local “Up” axis permanently maintained as vertical as possible. This tracking is similar to the billboard tracking in 3D. This is the preferred tracking constraint, because it has a more easily controlled constraining mechanism.
The “billboard tracking”
The term “billboard” has a specific meaning in real-time CG programming (i.e. video games!), where it is used for plane objects always facing the camera (they are indeed “trackers”, the camera being their “target”). Their main usage is as support for tree or mist textures: if they weren’t permanently facing the camera, you would often see your trees squeezing to nothing, or your mist turning into a millefeuille paste, which would be funny but not so credible…
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This constraint shares a close relationship to the IK constraint in some ways. This constraint is very important in rig design, and you should be sure to read and understand the tracking tutorial, as it centers around the use of both of these constraints.
[edit] Options
- To
- The axis of the object that has to point to the target.
- Up
- The axis of the object that has to be aligned (as much as possible) with the world Z axis. An Align: Target button, when enabled, uses the coordinates of the target object's Z axis, thus tilting or rocking the object as it tracks the target.
- Head/Tail - With Bone targets only
- A number from 0.0 to 1.0 that represents the place on the target bone to Track to (0.0 = the bone's root; 1.0 = the bone's head)
[edit] Example
 TrackTo example. |
 The Constraints panel of the example. |
(TrackTo example) is an example of a cube using the TrackTo constraint. Cube “A” is tracking “B” where “L” is the tracking line. Notice how the tracking object’s local axes are visible by using the Draw panel’s axis button. You can clearly see the tracking “To” and “Up” axis. Cube “A”’s constraint setting are reflected in (The Constraints panel of the example). +X is the “To” axis and Z is the “Up” axis.
You can also see in (The Constraints panel of the example) what cube “A” is tracking by looking at the Target field. We can see that cube “A” is tracking cube “B” because cube “B”’s name is “Cube”. You can redirect tracking to another object simply by entering in the name of another object.
[edit] Piston
Sample blend file
This constraint is also very useful to rotate the eyes of a character to make the character look at a fixed point. The same can be done for the camera or for lights.
![[]](/skins/blender/open.png)
