title: Poincaré Index Method (fingerprint singular points)
body: <p>I'm working on a  biometric project and i need to determine the singular points of a fingerprint. For this i use the Poincaré Index method described in <em>Handbook of Fingerprint Recognition</em>, D. Maltoni, D. Maio, K. Jain, S. Prabhakar and i am unable to understand the highlighted statement in the image below.</p>
  
  <p><a href="https://i.stack.imgur.com/5BF3N.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/5BF3N.png" alt="enter image description here"></a></p>
  
  <p>What i did was to determine the orientation map of my fingerprint image and then i simply added the differences between those values around a block. (divided the image in blocks of 13x13).But i am unable to determine the right points. 
   Can someone please explain the highlighted statement? Thank you.</p>