Rotating/Aligning parents relative to their children

Questions & Answers
1

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

119627-alignment-example.png
119627-alignment-example.png1280×720 15.8 KB

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?

2

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);