Hello,
I’m trying to Orient constrain one object to two others (FK-IK blending), all three objects have the same local rotation axes. If I Orient constrain the target object to either of the source objects individually everything works fine but when I try to constrain it to both of them it rotates strangely, I really don’t know what’s going on, any help would be hugely beneficial! I’m using the default option for the Orient constraint.
Thanks,
-Harry
This is because when you apply the constraint it is weighed fully to both targets by default. If you select the constraint node you will see 1.0 as the values for both blend target attributes (these weightings are normalised in the constraint computation so this is effectively 50% contribution to the result from each of the two targets).
In the attributes for the constraint you will also find an attribute called Interpolation Type which will be set to Average by default. So, your 180 degree flip is caused by the constraint being in a 0.5 blend through this averaged interpolation method. The best interpolation type to use depends on the needs of the setup, but for your example (IK/FK blend) generally “Shortest” should give you the best result.
Excellent, thanks for that; my background is in 3ds Max and there’s no choice of interpolation method. I still don’t understand why Orient constraining one object to two others in the same local space should cause any problems, it hasn’t done so in the arms but I’ll know now to use Shortest as the interpolation type.
-Harry
Your objects are not in the same local space. Saying they are in the same local space is the same as saying they have the same parent transform which is not true in your example. Their “Local rotation axes” align when maya draws them in worldspace but that is not the same thing. I believe in the case of your example what is happening is that your two target objects have different worldspace Rotations even though they have the same worldspace Orientation (i.e. one of them is one or more full rotations different to the other) and the Average interpolation method blends between Rotations while the Shortest interpolation method blends between Orientations.