title: fatal error: opencv2/xfeatures2d.hpp: No such file or directory
body: <p>I am trying to build this code:
  <a href="https://docs.opencv.org/3.2.0/d5/d6f/tutorial_feature_flann_matcher.html" rel="nofollow noreferrer">https://docs.opencv.org/3.2.0/d5/d6f/tutorial_feature_flann_matcher.html</a></p>
  
  <p>I am using Ubuntu 16.04 with CLion 2017.3 and have OpenCV 3.4 installed.</p>
  
  <p>xfeatures2d.hpp can't be found on the system.</p>
  
  <p>I have looked at many different problems on the internet, but couldn't find a solution.</p>
  
  <p>Any help? </p>