title: Get XYZ rotation from PVector
body: <p>I have a normalized <code>PVector</code> that represents a direction from the origin:</p>
  
  <pre><code>PVector dir = new PVector(-0.1, 0.8, 0.3);
  </code></pre>
  
  <p>I'd like to get the X, Y, and Z angles in that direction, so I can use the <code>rotateX()</code>, etc matrix transformations.</p>
  
  <p>In 2D, I'd use <code>atan2()</code> to get the angle, but I have no idea how to do this for a 3D point. </p>