FLANN error in OpenCV 3

Question

I am running Ubuntu 14.04. I am trying to run FLANN with openCV 3 but I get an error.

Everything bellow was tried by using AKAZE and ORB but the code if from my attempt to use ORB.

I use ORB to find the descriptors and key-points.

  Ptr<ORB> detector = ORB::create();

  std::vector<KeyPoint> keypoints_1, keypoints_2;
  Mat descriptors_1, descriptors_2;

  detector->detectAndCompute( img_1, noArray(), keypoints_1, descriptors_1 );
  detector->detectAndCompute( img_2, noArray(), keypoints_2, descriptors_2 );

After I use ORB, I use the following code to find matches:

  FlannBasedMatcher matcher;
  std::vector<DMatch> matches;
  matcher.match(descriptors_1, descriptors_2, matches);

The code builds fine and everything. When I run the code I get this error:

OpenCV Error: Unsupported format or combination of formats (type=0
) in buildIndex_, file /home/jim/opencv/modules/flann/src/miniflann.cpp, line 315
terminate called after throwing an instance of 'cv::Exception'
  what():  /home/jim/opencv/modules/flann/src/miniflann.cpp:315: error: (-210) type=0
 in function buildIndex_

Aborted (core dumped)

Can anybody tell me why? Is it something with OpenCV 3 being in BETA state? Is there an alternative to FLANN (except BFMatcher)

Answer 1

So what I said:

in order to use FlannBasedMatcher you need to convert your descriptors to CV_32F:

if(descriptors_1.type()!=CV_32F) {
    descriptors_1.convertTo(descriptors_1, CV_32F);
}

if(descriptors_2.type()!=CV_32F) {
    descriptors_2.convertTo(descriptors_2, CV_32F);
}

you can take a look to this similar question: