BFMatcher knnMatch

brute-force, c++, opencv

Solution

please have another look at the docs

while the ordinary match function has a `vector<DMatch>` as result,

knnMatch (say loud : k-nearest-neighbours !) results in several(k) vectors, thus you need a :

vector< vector< DMatch > > matches

for the result

Problem

I try to implement knnMatch on BFMatcher as follows: ``` BFMatcher matcher(NORM_L2, true); vector<DMatch> matches; //matcher.match(descriptors1, descriptors2, matches); matcher.knnMatch(descriptors1, descriptors2, matches, 2); ``` And receive the following error: ``` fiducialMain.cpp: In function ‘void fiducialCalc(cv::Mat, cv::Mat, cv::Mat&, cv::Mat&, int&)’: fiducialMain.cpp:98:56: error: no matching function for call to ‘cv::BFMatcher::knnMatch(cv::Mat&, cv::Mat&, std::vector<cv::DMatch>&, int)’ matcher.knnMatch(descriptors1, descriptors2, matches,2); ^ fiducialMain.cpp:98:56: note: candidates are: In file included from fiducialMain.cpp:15:0: /usr/local/include/opencv2/features2d/features2d.hpp:1116:18: note: void cv::DescriptorMatcher::knnMatch(const cv::Mat&, const cv::Mat&, std::vector<std::vector<cv::DMatch> >&, int, const cv::Mat&, bool) const CV_WRAP void knnMatch( const Mat& queryDescriptors, const Mat& trainDescriptors, ^ /usr/local/include/opencv2/features2d/features2d.hpp:1116:18: note: no known conversion for argument 3 from ‘std::vector<cv::DMatch>’ to ‘std::vector<std::vector<cv::DMatch> >&’ /usr/local/include/opencv2/features2d/features2d.hpp:1130:18: note: void cv::DescriptorMatcher::knnMatch(const cv::Mat&, std::vector<std::vector<cv::DMatch> >&, int, const std::vector<cv::Mat>&, bool) CV_WRAP void knnMatch( const Mat& queryDescriptors, CV_OUT vector<vector<DMatch> >& matches, int k, ^ /usr/local/include/opencv2/features2d/features2d.hpp:1130:18: note: no known conversion for argument 2 from ‘cv::Mat’ to ‘std::vector<std::vector<cv::DMatch> >&’ ``` Can anybody explain this error?

Original source