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Hi I have an arbitrary rotation quaternion, which is constructed from a series of operations done by the user (they select the object, rotate it around the plane constructed from the camera view direction, then maybe rotate it from another angle etc).

I then need to decompose this rotation object down into a rotation around the X, Y and Z axes. Note that it doesn't have to be that order. The user interface allows a user to attach rotation blocks together in any order, so they could chain them up like this:

enter image description here

In code, I then loop through each block and do:

finalRotation *= Quaternion.CreateFromAxisAngle(blockAxis, toRadians(blockAngle))

So how could I convert an arbitrary quaternion back to this block representation? I've tried projecting the quaternion onto the X, Y and Z planes as per this answer:

Component of a quaternion rotation around an axis

and then connecting up the blocks in an [X][Y][Z] order, but so far the results seem to come out incorrectly. Would someone be able to explain how I should approach this problem? Note I am restricted to rotating around one axis at a time, per block.

Edit: To clarify I am using the MonoGame framework, not Unity.

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  • Did you try Quaternion.eulerAngles and Quaternion.ToAngleAxis ? One of them should work for you. Commented Aug 7, 2017 at 21:32
  • Sorry not using the Unity Engine, made an edit Commented Aug 7, 2017 at 21:33
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    The Quaternion implementation in the Monogame framework appears to be a copy of that from the System.Numerics namespace, both for which I cannot seem to find any method to convert to Euler angles either. Have a look at my implementation if you want to use the same logic. Commented Aug 7, 2017 at 22:15
  • @Biscuits In this case I re-apply each angle of rotation as a quaternion, not all at once in a YawPitchRoll method. Anyway I looked at your code, and just want to point out that your ToEulerAngles() function doesn't account for gimbal lock so won't work for all angles, and your GetAxis() function doesn't account for singularity cases either so you'll have problems when angle = 0/180. Commented Aug 8, 2017 at 13:39
  • I know you don't have unity, but can't you load up the Unity framework so you have their library on your dev machine, and then reflect the Quaternion.eulerAngles method to see the code behind it and learn how its done? Commented Aug 9, 2017 at 1:11
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