Add a quaternion to euler angles

In a game I want to display a rotation of an object. The user can then rotate the object by selecting an arbitary axis and dragging this axis by an angle (angle axis). After that the change by this rotation is calculated as a quaternion.

Code (CSharp):

1. var rot = Quaternion.AngleAxis(angle, axis); // get the desired rotation
2.  
3. // apply rotation to object
4. transform.rotation *= Quaternion.Inverse(myRot) * rot * myRot;
5. totalEulerAngles = AddQuaterionToEuler(totalEulerAngles, rot); // <-- this function is needed

The rotation is displayed ingame as an euler angle. I could convert the resulting quaternion for this. However the euler angle will always be wrapped between 0 and 270 for each axis and {x: 180, y: 180, z: 0} might be displayed as {x: 0, y: 0, z: 180}.

So a function is needed AddQuaternionToEuler that adds a quaternion to an existing euler angle. The resulting euler angle should be the total rotation with more then 360 degrees possible if the user rotates the object around itself.

I have been searching for some hours for this but didn't find any approach on doing this.

 

In general, you could convert the Quaternion to Euler angles, then add the vectors.

totalEulerAngles = totalEulerAngles + rot.eulerAngles

But in your particular situation, you started with an axis rotation and converted it to a Quaternion. Rather than doing a round-trip conversion process that might-or-might-not give you back the original value...why not just add the original angle to the appropriate axis?

Also, this line:

transform.rotation *= Quaternion.Inverse(myRot) * rot * myRot;

is just a complicated and expensive way of doing

transform.rotation = rot * myRot;

But if you're going to maintain a totalEulerAngles variable, you should probably instead use

transform.eulerAngles = totalEulerAngles;

otherwise, it's possible your Quaternion and your totalEulerAngles might slowly drift apart due to floating point error in the conversion process. (Probably not, but why give it the chance? Also, this approach probably save a little bit of math.)

 

if I understood this correctly, what you're missing is how to add two quaternions together to create a compound rotation.

Code (csharp):

1. var originalRotation = Quaternion.AngleAxis(angle, axis);
2. var someUserRotation = Quaternion.Euler(eulerAngles);
3. var compoundRotation = originalRotation * someUserRotation;
4. // apply compoundRotation to object

edit:
nah I was mislead by your further explanation, check out Antistone's solution

 

actually, it appears to be just

transform.rotation *= rot;

Quaternion.Inverse(myRot) and myRot effectively cancel each other out

 

Thank you thats what i was searching for!