欧拉角 Y 值受 X 和 Z 值的影响 - 如何将它们归零以获得“真实”的 y 值？

Question

The effect I'm trying to achieve is to have an arrow pointed out from the camera's pointOfView position, aligned with the scene (and gravity) on the x and z axis, but pointing in the same direction as the camera. It might look something like this:

Right now, I have its euler angles x and z set to 0 , and it's y set to match that of the ARSCNView.pointOfView.eulerAngles.y . The problem is that as I rotate the device, the eulerAngles.y can end up having the same value for different points. For example, facing the device in one direction, my eulerAngles are:

x: 2.52045, y: -0.300239, z: 3.12887

Facing it in another direction, the eulerAngles are:

euler angles x: -0.383826, y: -0.305686, z: -0.0239297

Even though these directions are quite far apart, the eulerAngles is still pretty much the same. The different x and z values mean the y value doesn't represent which direction the device is facing. As a result, my arrow follows the camera's heading to some point, and then starts rotating back in the opposite direction. How can I zero-out the x and z values in a way that I'll get a truthful y value, that I can then use to orient my arrow?

Answer 1

Do not use euler angles to detect 'real' or 'truthful' values.

Those values are always correct. To work with rotation you have to use either matricies or quaternions.

Remember. It is possible to define lots of 'euler angles' using matrix.

Each euler angle is relative to the previous one.

SceneKit applies these rotations in the reverse order of the components:

 1. first roll 2. then yaw 3. then pitch

So, to calculate the value you angle I would suggest to calculate the vector and its projection to Oxy plane. This angle is not 'euler' angle.