Programmatically get center of rotation

Hey there!
We’re developing a rhino plugin and we need to know the center of a rotation, when the user rotates an object.
We’re using C++ and Rhino 5.

What we’ve done so far:

  • We subclassed CRhinoOnTransformObject and get the transformation matrix of an arbitrary transformation.
  • We analyze the transformation matrix to find out, if it was a rotation and then calculate the rotation’s quaternions accordingly.

Is there a way to get more details about a transformation, at least the center of a rotation?

Note that the center of rotation may change from one rotation to the next, for instance when using a space mouse that automatically re-calculates this at each operation (maybe even during an operation).