title: What is "Uncaught TopologyError: no outgoing dirEdge found" in Turf.js?
body: <p>I am attempting to use <code>turf.concave</code> to get a polygon. It works with most of the points I put in, but with one set of points, it takes offense and throws the following error:</p>
  
  <p><code>Uncaught TopologyError: no outgoing dirEdge found [ (-121.9717867, 47.73397465) ]</code></p>
  
  <p>The file with the data I am attempting to use is located <a href="https://github.com/samcorcos/campaign-hawk/blob/master/precinct4.geojson" rel="nofollow">here</a>.</p>
  
  <p>The function is simply:</p>
  
  <p><code>turf.concave(&lt;mygeojson&gt;, 1, 'miles')</code></p>
  
  <p>And, as I said, it works with all the other FeatureCollections. Any idea why it wouldn't work with this one?</p>