How to rotate mesh by aligning normal with axis?

Questions
1

I have a mesh that has been arbitrarily rotated. I would like to rotate it so that it is flat on the ground. My idea is to find the closest normal to the y-axis and then align that normal to the axis. I’m using a widely accepted answer on Stackoverflow as a basis: math - Finding quaternion representing the rotation from one vector to another - Stack Overflow

However, I am getting a weird skewed result instead of the rotation that I would expect. After the rotation, I would expect the normal of the blue face to be (0, 1, 0) (aligned to the y-axis). If you comment out line 50, you can see what the box looks like before applying the quaternion.

Does anyone have experience with this? I’m afraid there is likely just something I don’t understand about quaternion rotations happening here.

2

Small update: normalizing the resulting quaternion fixes the weird skewing I was seeing, but still does not align the mesh like I’d expect.

3

This may be of use

4

Thanks! That did get me on the right track to conceptually understand what was happening. It turns out, I was also using the wrong method to do the actual quaternion rotation.

Solved here :slight_smile:

5

I’ve made an alternate implementation using the method @JohnK referenced. I found the ‘normal’ you used odd, since it isn’t normal to Y - perhaps it’s just in the plane of the normal you want. I find the RotationFromAxis method easier to understand and use in my code, but that’s maybe just me.

3 Likes
6

Thanks so much for the alternate implementation! I marked yours as solution because I do like the RotationFromAxis method a bit more. Thanks for the suggestion