what type of data does flann index need by using LshIndexParams?

Question

I want to use LSH to speed up the searching,and i found in opencv flann can do this,by using LshIndexParams? The problem is i cannot get the format right. i use bag of words to generate a mat output and feed it to flann, but i get errors all the time.

OpenCV Error: Unsupported format or combination of formats (type=2

) in buildIndex_, file /home/vampire/opencv-2.4.8/modules/flann/src/miniflann.cpp, line 315 terminate called after throwing an instance of 'cv::Exception' what(): /home/vampire/opencv-2.4.8/modules/flann/src/miniflann.cpp:315: error: (-210) type=2 in function buildIndex_

part of the code likes this:

    Mat img_BOWdescriptor=BOW_descriptors(path);
cout<<img_BOWdescriptor<<endl;
img_BOWdescriptor.convertTo(img_BOWdescriptor,img_BOWdescriptor.rows,img_BOWdescriptor.cols,CV_32F);
cout<<img_BOWdescriptor<<endl;
cout<<"done"<<endl;

cout<<"ini flann index......"<<endl;
Mat indices = Mat(img_BOWdescriptor.rows, 1, CV_32S);
Mat dist = Mat(img_BOWdescriptor.rows, 1, CV_32F);
descriptors_all.convertTo(descriptors_all,descriptors_all.rows,descriptors_all.cols,CV_32F);

flann::Index* flann_index=new flann::Index(descriptors_all,flann::LshIndexParams(20,10,2));
cout<<"done"<<endl;
double t=(double)getTickCount();

cout<<"flann matching......"<<endl;
flann_index->knnSearch(img_BOWdescriptor, indices, dist, 1,flann::SearchParams(32));

and i also tried to convert to other type, no one works, does any one know how to do it? and after i get result,how can i know if it matches?

Answer 1

Give a try. I think i had the same error, Mine works with an extra parameter:

cv::flann::Index kVecinos(descriptors, cv::flann::LshIndexParams(12, 20, 2), cvflann::FLANN_DIST_HAMMING);

in cvflann there is also others like cvflann::FLANN_DIST_EUCLIDEAN