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Damped track normal behaviour ?
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I used a camera which follows a nurbs path and 'damped track' to an empty.

At some moments on the path the camera rotates around its Z axis in a way that seems not what we could expect (I think ?), especially considering the associated tooltip which says : "points toward a target performing the smallest rotation necessary".

You can see a gif of it here :

The blend file :


Event Timeline

I suspect this has something to do with the fact that there are infinitely many 'shortest' rotations between two exactly opposite vectors, together with some kind of numeric precision problems.

On the principle, I disagree as 3 vectors are in the game here. My 'interpretation' is that all vectors may stay as stable as possible.

There aren't 3 vectors here. Damped Track is a very confusing name for a look at constraint, which finds minimal one axis rotation to point one vector to another. Track To is the one that uses an up vector too.

OK, I can accept it. But so 'Damped Track' is a kind of 'Track To' for which the 'Up' part could be set to none ? Or is there a more subtle things under that ?

Track To is more mechanical motion like on a camera tripod with rotation around the fixed up vector, then pitching up and down. Damped Track is similar to attachment by a flexible rod that can bend in any direction, but completely resists twist. It is thus very useful in rigs for separating bone rotation into pure bending at the base of the joint and twist further along.

OK Alexander, thanks a lot. Do I have to close my question ? I don't know how it works for that here.

Bastien Montagne (mont29) changed the task status from Unknown Status to Unknown Status.Jul 29 2016, 7:15 PM
Bastien Montagne (mont29) claimed this task.

This is also affected by the type of Twisting used by your path - but yes, all in all this is instability we cannot really fix with current constraint design. Thanks for the report anyway.