title: matplotlib contour/contourf of **concave** non-gridded data
body: <p>I'd like to do a matplotlib <code>contour</code> or <code>contourf</code> plot of non-gridded 3D data (x, y, z) which is somehow C-shaped in x and y (see sketch) -- therefore part of the enclosing hull around the data is concave in x and y.</p>
  
  <p>Usually I do plots of non-gridded 3D data by first interpolating it with</p>
  
  <pre><code>from matplotlib.mlab import griddata
  griddata...
  </code></pre>
  
  <p>but this generates artifacts in the concave part of the data such that the concave part is filled by the interpolation.</p>
  
  <p><strong>Is it possible to do the interpolating or contourf/contour plots such that 
  the concave part of the data is respected?</strong></p>
  
  <p><a href="https://i.stack.imgur.com/WKP4C.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/WKP4C.png" alt="enter image description here"></a></p>