title: OpenCV - approxPolyDP for edge maps (not contours)
body: <p>I have successfully applied the method cv::approxPolyDP on contours (cv::findContours), in order to represent a contour with a simpler polygon and implicitly do some denoising.</p>
  
  <p>I would like to do the same thing on an edge map acquired from an RGBD camera (which is in general very noisy), but with not much success up to now and I cannot find relative examples online. The reason I need this, is that by means of an edge map one can also use the edges between fingers, edges created by finger occlusion or edges created in the palm.</p>
  
  <p>Is this method applicable to general edge maps, other than contours?</p>
  
  <p>Could someone pinpoint me to an example?</p>
  
  <p>Some images attached:</p>
  
  <p>Successful example for contours:
  <img src="https://i.stack.imgur.com/rjO38.png" alt="enter image description here"></p>
  
  <p>Problematic case for edge maps:</p>
  
  <p>Most probably I draw things in the wrong way, but drawing just the pixels returned by the method shows that probably large areas are not represented in the end result (and this doesn't change much according to the epsilon-parameter).</p>
  
  <p><img src="https://i.stack.imgur.com/58Bcc.png" alt="enter image description here"></p>
  
  <p>I attach also a depth image, similar to the ones I use in the experimental pipeline descibed above. This depth image was not acquired by a depth camera, but was synthetically generated by reading the depth buffer of the gpu, using OpenGL.</p>
  
  <p><img src="https://i.stack.imgur.com/mA9EE.png" alt="enter image description here"></p>
  
  <p>Just for reference, this is also the edge map of the depth image acquired straight from the depth camera (using the raw image, no smoothing etc applied)</p>
  
  <p><img src="https://i.stack.imgur.com/tptxn.png" alt="enter image description here"></p>
  
  <p>(hand as viewd from a depth camera, palm facing upwards, fingers "closing" towards the palm)</p>