title: D3.js radial text
body: <p>In d3.js how can a align text like in the figure ?</p>
  
  <p>I have an arc and I want to place the text "radial" to this arc.
  The origin is the black dot and the data of the arc is radius and [start(radians),end(radians)].</p>
  
  <p>In advance, thanks!
  <a href="https://i.stack.imgur.com/89XCs.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/89XCs.png" alt="radial text"></a></p>
  
  <p>the code (partial):</p>
  
  <pre><code>...
  var arc = d3.svg.arc()
          .innerRadius(0)
          .outerRadius(ras2)
          .startAngle(d.sa * Math.PI)
          .endAngle(d.sb * Math.PI);
     svg.append("path")
          .attr("class", "arc")
          .attr("d", arc)
          .attr("fill","red");
  ...
  </code></pre>