title: cv2.approxPolyDP() , cv2.arcLength() How these works
body: <p>How do these function works? I am using Python3.7 and OpenCv 4.2.0. Thanks in Advance.</p>
  
  <pre><code>approx = cv2.approxPolyDP(cnt, 0.01*cv2.arcLength(cnt, True), True)
  </code></pre>