title: OpenCV xfeatures2d_SURF -213:The function/feature is not implemented
body: <p>I'm on Windows 10 and installed python3 and added OpenCV and OpenCV-contrib via pip. For the xfeatures_2d it gives the following error. </p>
  
  <p>Can I add that option using pip? </p>
  
  <pre><code>detector = cv.xfeatures2d_SURF.create(hessianThreshold=minHessian)
  </code></pre>
  
  <p>cv2.error: OpenCV(3.4.3) C:\projects\opencv-python\opencv_contrib\modules\xfeatures2d\src\surf.cpp:1016: error: (-213:The function/feature is not implemented) This algorithm is patented and is excluded in this configuration; Set OPENCV_ENABLE_NONFREE CMake option and rebuild the library in function 'cv::xfeatures2d::SURF::create'</p>