title: How can I get convert a 3D point in a HelixToolkit Viewport3DX to a 2D position?
body: <p>Simple question with I expect not a very simple answer.</p>
  <p>I have a Viewport3DX, and I'd like to be able to convert a point in there, i.e. 0.5, 0.7, 1.2 for x/y/z to a 2D position in the window, taking into account the camera/zoom etc.</p>
  <p>Is there a built in way to do this in HelixToolkit/Viewport3DX?</p>
  <p>Cheers</p>
  <p>Garry</p>