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If I rotate an empty I would expect to see the same rotation on the x,y and z axis for child and parent, but I see the rotation for the empty in the xyz rotation fields but the child xyz rotation fields stay 0,0,0. Is that logical ??

enter image description here

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  • $\begingroup$ I think you mean "the child xyz rotation fields stay 0,0,0" right? $\endgroup$
    – PGmath
    Jan 20, 2016 at 17:02
  • $\begingroup$ May I ask why you focus on an empty? Do other objects behave differently? Anyway, here's a related question (about location instead of rotation): Location of object wrong? $\endgroup$
    – Carlo
    Jan 20, 2016 at 17:08

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Yes, this is exactly what is supposed to happen.

The transform values shown under the Object Properties panel are the local transformations of the object. All inherited transformation is applied in global space, not local space. This is why if you un-parent an object it will snap back to it's original location unless you choose to keep transformation.

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Matrix Multiplication

Yes its logical because you are seeing factors of a multiplication in the info panels and you see the result visualized in the 3D View.

The final location/rotation/scale of the child is a composite of the parent matrix and the child matrix. The matrices are multiplied in an appropriate fashion. You see the final result in the 3D View window. If the parent has uniform scale 8 and the child has uniform scale 2 then the scale result you see in the 3D View window is 16 = 8 * 2. You see the 8 and 2 in the object rotation info. You might see some useful information in the dimension info as well.

If you had a chain of parents of length 2 with uniform scales of 5 and 8 with the child of uniform scale 2 you would expect to see a final visualization of 80 = 5 * 8 * 2. So with more complex chains showing the factors is quite useful and necessary.

Of course I can not do justice to the matrix multiplication math that has been around for quite some time and can occupy a few chapters in a 3D computer graphics book.

A video. I am just providing a starting point for you in limited time. I am not trying to promote a particular video. You will decide what entertains you.

https://www.youtube.com/watch?v=PpkTpGH-O40

Wikipedia Reference

I am not stating that what is linked below is trivial reading the first time. There are some nice pictures in some of the references.

https://en.wikipedia.org/wiki/Rotation_matrix

https://en.wikipedia.org/wiki/Scaling_%28geometry%29

https://en.wikipedia.org/wiki/Translation_%28geometry%29

https://en.wikipedia.org/wiki/Transformation_matrix

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