From which axes are the rotation values in the timeline panel measured for a 3D layer?

[interesting_Gleam1519]

I don't quite understand from which axes are the rotation values in the timeline panel of a 3D layer measured? I used to think that the Z rotation is measured from the normal vector of the layer, and X and Y rotations from the X and Y axes in the plane of the layer and mutually perpendicular to the normal vector. But this experiment (linked video) shows otherwise.

In the experiment above, I changed the Y rotation value first, but upon changing the X rotation value the layer doesn't seem to rotate about the transformed X axes (which was transformed due to the Y rotation), rather it rotates about the X axes parallel to the comp's X axis. 

I'm certainly missing something.

GPT told something like rotation values are calculated in an order. Always x first, y second, and then z, and that's the reason why the final result looks like this. That even though you've made the x rotation after the Y rotation it would still be calculated as x first then y. I sure can't trust that though.

[Kevin-Monahan]

Hi,

Thanks for the question.

In After Effects, 3D rotations always happen in a fixed order: X first, then Y, then Z. Even if you change Y rotation before X, the program still applies X rotation first around the comp’s original X axis—not the layer’s rotated X axis.

So the layer never spins around “transformed” axes like you might expect. It always rotates around the fixed comp axes in that order, which is why your experiment looks the way it does. It’s just how AE keeps things consistent and avoids weird rotation issues.

I hope this makes sense.

Thanks,
Keviun

[interesting_Gleam1519]

Thank you, that certainly clears things up.

I'm just still not sure from what axes are the rotations measured. Could you just pin point that for me?

There're a lot of axes and I'm quite confused which are the rotation axes. There's the composition space axes - X,Y,Z mutually perpendicular with their origin at the comp's top left. There's the layer space axes, X,Y,Z mutually perpendicular centered at the top left of the layer -  from the origin of which the anchor point coordiantes are measured. Then there are axes that originate from the anchor point about which the rotation happens - this is what I'm not sure about - what are these axes exactly how are they oriented, are they fixed, or rotate with rotation. 

[Roland Kahlenberg]

This video may help with the different view axes modes - 

[Rick Gerard]

If you want to rotate according to the layer axis and maintain independence, you have to change the Set Rotation tool from the Default Orientation to Rotation, and then grab the Red ring for X rotation, the Green ring for Y, or the Blue ring for Z rotation about the layer axis. 

Because the X, Y, and Z properties are linked, changing the rotation value by grabbing the rings on the Layer's Position icon will then change the selected X, Y, or Z value and maybe one or both of the other rotation values to properly orient the layer around the Anchor Point. There is some complex math going on there, but the values will be the same that they would be if you went from 15, 15, 15 to 45, 45, 45 by manipulating the X, Y, and Z values in the timeline, and the animation would look the same. I find it easier to use the Rotation tool (w), change the Rotation property at the end of the toolbar from Orientation to Rotation, and then continue to use the Rotation tool or the Selection Tool (v) to set keyframes on a 3D layer when I need to animate rotation. I hardly ever use the timeline values unless I need to achieve a specific rotation or orientation.

Does that make sense? It took me a while to figure out what was going on when we first got 3D layers in After Effects, but it makes sense to me now. 

[Roland Kahlenberg]

After Effects uses two types of calculations - Euler for Rotation and Quarternion for Orientation. Google these and you should have a better idea of what's happening under-the-hood. Also, as a general rule of thumb, use Orientation to set poses (largely because it doesn't go beyond 360 degrees on an axis) and Rotation for animation.

HTH