title: Is there any "Geometry Contour Line Algorithm"?
body: <p>I want to find &amp; draw contour lines like this.</p>
  <p><a href="https://i.stack.imgur.com/f0Fa1.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/f0Fa1.png" alt="" /></a></p>
  <p>Data is just List of (x,y,z) and only a few points (about 40~60) in there.
  (x and y are position and z is height)</p>
  <p>How can i find this contour line and point?</p>