title: How to get coordinates of slices along the edge of a pie chart?
body: <p>I am creating a piechart with D3 using <code>d3.layout.pie()</code>. 
  It looks like this one, without black dots (I've put them manually in Photoshop to illustrate my issue). I wonder how I can calculate coordinates of these dots, that are in the middle of the surface to place some tooltips there. I am not asking for a finished solution but more about the principle how to do it.
  Thanks.</p>
  
  <p><img src="https://i.stack.imgur.com/eFHwZ.png" alt="Circle chart"></p>