C++ – How to use SIFT in OpenCV 3.0 with c++

c++opencvopencv3.0sift

I have OpenCV 3.0, and I have compiled & installed it with the opencv_contrib module so that's not a problem. Unfortunately the examples from previous versions do not work with the current one, and so although this question has already been asked more than once I would like a more current example that I can actually work with. Even the official examples don't work in this version (feature detection works but not other feature examples) and they use SURF anyway.

So, how do I use OpenCV SIFT on C++? I want to grab the keypoints in two images and match them, similar to this example, but even just getting the points and descriptors would be enough help. Help!

Best Solution

  1. get the opencv_contrib repo
  2. take your time with the readme there, add it to your main opencv cmake settings
  3. rerun cmake /make / install in the main opencv repo

then:

   #include "opencv2/xfeatures2d.hpp"

  // 
  // now, you can no more create an instance on the 'stack', like in the tutorial
  // (yea, noticed for a fix/pr).
  // you will have to use cv::Ptr all the way down:
  //
  cv::Ptr<Feature2D> f2d = xfeatures2d::SIFT::create();
  //cv::Ptr<Feature2D> f2d = xfeatures2d::SURF::create();
  //cv::Ptr<Feature2D> f2d = ORB::create();
  // you get the picture, i hope..

  //-- Step 1: Detect the keypoints:
  std::vector<KeyPoint> keypoints_1, keypoints_2;    
  f2d->detect( img_1, keypoints_1 );
  f2d->detect( img_2, keypoints_2 );

  //-- Step 2: Calculate descriptors (feature vectors)    
  Mat descriptors_1, descriptors_2;    
  f2d->compute( img_1, keypoints_1, descriptors_1 );
  f2d->compute( img_2, keypoints_2, descriptors_2 );

  //-- Step 3: Matching descriptor vectors using BFMatcher :
  BFMatcher matcher;
  std::vector< DMatch > matches;
  matcher.match( descriptors_1, descriptors_2, matches );

also, don't forget to link opencv_xfeatures2d !