Scenekit: Angle between two SCNNode
<p>I am trying to develop a robotic arm tracking system.
I used scenekit to develop the visualization and the control of the system.
The SCNNodes of my system is: </p>

<p>Shoulder--->Upper_arm--->Fore_arm--->Palm.</p>

<p>I could now rotate each node using the <code>rotation property of each SCNNode.</code></p>

<p>And I am now interested in whether there's any existing API to <code>compute the angle between two SCNNode</code> when the system is moving, eg. the angle between the Upper_arm and Fore_arm? </p>