title: rotate a projection to follow mouse drag
body: <p>I'm working on a project to generate world map projections and manipulate them. You can see a beta version here : <a href="http://ansichtssache-n.ch/en/personas/daVinci" rel="nofollow">http://ansichtssache-n.ch/en/personas/daVinci</a></p>
  
  <p>I'm trying to get the drag event correctly interpreted, so that for example when you drag Australia up, it actually moves Australia up and not the center of the projection (causing Australia to move down in a Miller projection).</p>
  
  <p>I've been trying to find the correct rotation angles to apply to the 3 axis as shown here <a href="http://bl.ocks.org/mbostock/4282586" rel="nofollow">http://bl.ocks.org/mbostock/4282586</a> .</p>
  
  <p>I can get the x/y position on the canvas from the start and end of the mouse drag, I can get the geo-coordinates of these points too, and I can get the x/y of the current center as well as its geo-coordinates, but honestly I'm stuck now...</p>
  
  <p>Any idea ?</p>