An alternate method of determining high-quality feature matches is the ratio test proposed by David Lowe in his paper on SIFT (page 20 for an explanation). This test rejects poor matches by computing the ratio between the best and second-best match. If the ratio is below some threshold, the match is discarded as being low-quality.
std::vector<std::vector<cv::DMatch>> matches;
cv::BFMatcher matcher;
matcher.knnMatch(descriptors_1, descriptors_2, matches, 2); // Find two nearest matches
vector<cv::DMatch> good_matches;
for (int i = 0; i < matches.size(); ++i)
{
const float ratio = 0.8; // As in Lowe's paper; can be tuned
if (matches[i][0].distance < ratio * matches[i][1].distance)
{
good_matches.push_back(matches[i][0]);
}
}