title: Get rgl view parameters
body: <p>While the <code>view3d(theta, phi,...)</code> function can be used to rotate the viewing point to a suitable location while taking snapshot of 3d charts/objects, it's quite hard to guess which theta and phi values are good. </p>
  
  <p>Once the plot is shown, we can interactively rotate it. But is there anyway to find out the theta and phi parameters of the plot after manual rotation, such that we can use it programmatically (i.e. when creating many plots that should be of the same viewpoint)?</p>