title: Calculate 3D Euler angle between two 3D vectors?
body: <p>Say I have 2 3D vectors, each describing a direction in 3D space (or a rotation, but I'm not sure if that terminology is correct). How would I calculate the difference between the two vectors as an Euler angle? That is, if I applied the angle to the first vector, it would rotate to equal the other? I understand how Euler angles have issues and are implementation-dependant, but I don't know what the implications of this are on a question such as mine.</p>
  
  <p>To clarify a little, when I say "3D vectors", I'm picturing the "translation" gizmo you get in most 3D modelling packages or in Unity (which is what I'm using).</p>
  
  <p><strong>EDIT:</strong> Actually I just reviewed the "vectors" that I'm using, and what I said is not quite correct. I actually have 6 vectors, 3 for each rotation. Each vector is a position in 3D space offset from the centre of rotation. This probably makes an already-difficult question near-impossible, right?</p>
  
  <p><strong>ADDITIONAL INFORMATION:</strong> Ok, so I've worked out what I actually want to ask (because <em>this</em> question is really badly done), and it applies more to Unity, so I've asked a more Unity-specific question <a href="http://answers.unity3d.com/questions/697934/calculate-differential-euler-angles-from-two-trans.html" rel="nofollow">over on Unity Answers</a>. </p>
  
  <p>I'm don't normally understand mathematical formulae that are posted online, so C++-styled pseudo-code would be by far the most helpful for me.</p>
  
  <p>Any help would be much appreciated, and if my question lacks certain information, please just ask for more :)</p>