Quaternion.AngleAxis

Questions & Answers
1

I was tinkering a bit with the MouseLook.cs from the Unity StandardAssets.

They have some code that uses Quaternion.AngleAxis, more specifically:

Quaternion xQuaternion = Quaternion.AngleAxis (rotationX, Vector3.up);

What I need to do is if I have the xQuaternion, what sort of math would I have to do to get the rotationX instead of the xQuaternion. In other words, how would I do the reverse of this line of code. What I need to do, is I am using this code to move my camera, and I am sometimes switching to another camera mode which can also move the camera around. When I switch back however, I want to set the values of rotationX and rotationY to be the new rotation of the camera so that the camera doesn’t “jump” back.

2

You can use its inverse function, Quaternion.ToAngleAxis:

var angle: float; // the variables must exist, because they will
var axis: Vector3; // be passed by reference (result stored in them)
xQuaternion.ToAngleAxis(angle, axis);

or in C#:

float angle;
Vector3 axis;
transform.rotation.ToAngleAxis(out angle, out axis);

SIDENOTE: A quaternion is a math representation of a single rotation of some angle about an arbitrary axis, thus converting from and to the angle-axis format is always possible.