Rotating/Aligning parents relative to their children

Question

Hello all. I have having some trouble alinging two parent objects, according to their child objects.

alt text In this picture, the blue squares are the parents, while the red dots are the children I am trying to align by. The yellow line is the rotation of the children.

Positioning them at the same world spot is easy,

     parentPosition =otherParentsChildWorldPos- thisParentsChildsLocalPosition;

Now rotating them so that the rotation are the inverse of each other is proving to be more difficult. I have tried ways such as

     var desiredRot = otherChild.transform.eulerAngles - thisChild.transform.eulerAngles;
 
     var offsetBetweenParentAndItsChild= thisChild.transform.localEulerAngles;
         parent.transform.rotation = Quaternion.Euler(-otherChild.transform.eulerAngles + offsetBetweenParentAndItsChild);

But it provides wonky results when you rotate the parent from a rotation other than 0,0,0.

Any ideas?

A possible theory are somehow treating the child position as the origin on the parent (even when it's not), and rotating from there?

Answer 1

Answer by ahstein · Jun 26, 2018 at 11:14 PM

Shouldn't the local Euler angles for the red dots always be (0,0,0)? Are you rotating the red dots independently of their parents?

If the red dots are in a fixed position relative to the origin of the parents, then you can use that as a "heading" for the object and use Quaternion.SetFromToRotation to find the correct rotation (multiply the target heading by -1 to rotate it by 180 deg).

Something like...

 transform.rotation *= Quaternion.SetFromToRotation(child.transform.localPosition, 
                                                  -1 * otherChild.transform.localPosition);

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Rotating/Aligning parents relative to their children

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