KMeans Clustering for vector<Point2f> Data Structure

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@IlSc: In a real scenario, one should use KMEANS_PP_CENTERS instead of KMEANS_RANDOM_CENTERS (and maybe more attempts).

@berak: Maybe Mat_<cv::Vec2f> would have worked?

@Guanta, like Mat_<Vec2f> centers; ? crashes in kmeans while copying.

@berak: thought of clustered_cetner = centers.at<cv::Vec2f>(idx) , since you commented that cv::Point2f doesnt work here, however I don't know if this works either, or did you mean sth else?

Mat(vector<Point2f>) gets wrapped to a Mat(npoints,2,CV_32F), and the resulting centers are a Mat(nclusters,2, CV_32F) . imho, there's no way to access it as either at<Point2f>() or at<Vec2f>() without the reshape() (but please, prove me wrong here ;)

@berak: hm, for me both variants work, but maybe I missunderstood you again:

cv::Point2f a(1,2);
cv::Point2f b(3,4);

std::vector<cv::Point2f > t;

t.push_back(a);
t.push_back(b);
cv::Mat tt(t);

std::cerr << tt.at<cv::Vec2f>(0) << std::endl;

std::cerr << tt.at<cv::Vec2f>(1) << std::endl;

std::cerr << tt.at<cv::Point2f>(0) << std::endl;

std::cerr << tt.at<cv::Point2f>(1) << std::endl;

(grml how do I add '<'/'>' in code, always the same...)

^^ true, that works. your tt is a Mat(2,1,CV_32FC2)

unfortunately, the centers are Mat(K,2,CV_32F), so let's reshape your example:

Mat t2 = tt.reshape(1,tt.rows);

tt.at<Point2f>(0); // fine

t2.at<Point2f>(0); // have a good laugh at the errormsg ;)

@berak: sry to disappoint you, but any of the following works for me (OpenCV 2.4.9):

cv::Point2f a(1,2), b(3,4), c(5,6);

static const cv::Point2f arr[] = {a, b, c};

std::vector<cv::Point2f> t(arr, arr+sizeof(arr)/sizeof(arr[0]));

std::cerr << "---\n";

cv::Mat tt(t);

std::cerr << tt.cols << " " << tt.rows << " " << tt.channels() << std::endl;

std::cerr << tt.at<cv::Vec2f>(1) << std::endl;

std::cerr << "---\n";

cv::Mat t2 = tt.reshape(1, tt.rows);

std::cerr << t2.cols << " " << t2.rows << " " << t2.channels() << std::endl;

std::cerr << t2.at<cv::Point2f>(1) << std::endl;

std::cerr << "---\n";

cv::Mat t3 = tt.reshape(1, 2);

std::cerr << t3.cols << " " << t3.rows << " " << t3.channels() << std::endl;

std::cerr << t3.at<cv::Point2f>(1) << std::endl;

Output:

---
1 3 2
[3, 4]
---
2 3 1
[3, 4]
---
3 2 1
[3, 4]

wow, you're right

something must be broken here ...

hey, @Guanta, thanks for taking that challenge (though the results are alarming...)

just can't do it on my own box.

cool link!