title: get the perimeter of a 2D set of points
body: <p>I have a set of points in 2D ( coordinates for x and y ), now I need to discard all the points that are not meaningful to me, and what I mean by that is that I'm only interested in the area that this points are tracing.</p>
  
  <p>In short, this</p>
  
  <p><img src="https://i.stack.imgur.com/4lI4B.png" alt="enter image description here"></p>
  
  <p>it's supposed to produce this</p>
  
  <p><img src="https://i.stack.imgur.com/WfjtL.png" alt="enter image description here"></p>
  
  <p>question: what algorithm can do this kind of filtering on this points ?</p>