OpenCV C++ usage of cv::Moments

c++, image-processing, opencv

Solution

Using moments to find a centroid is a bit overkill imho. You can use the following algorithm to do it:

sumX = 0; sumY = 0;
size = array_points.size;
if(size > 0){

    foreach(point in array_points){
        sumX += point.x;
        sumY += point.y;
    }

 centroid.x = sumX/size;
 centroid.y = sumY/size;
}

Or with the help of Opencv's boundingRect:

//pseudo-code:

Rect bRect = Imgproc.boundingRect(array_points);

centroid.x = bRect.x + (bRect.width / 2);
centroid.y = bRect.y + (bRect.height / 2);

Problem

I try to find centroid using OpenCV C++'s cv::Moments. Whatever arguments I submit to it, All I receive back are zeros. Clearly I do something very simply wrong. Output of code: ``` 23 of 500 elements in unit 3 point values 2.976444 18.248287 matrix size 23 moments 0.000000 0.000000 0.000000 0.000000 0.000000 0.000000 0.000000 0.000000 moments 0.000000 0.000000 0.000000 0.000000 0.000000 0.000000 0.000000 ``` And code: ``` printf("%d of %d elements in unit %d\n",k,number_of_features,i); cv::Mat x(k, 1, cv::DataType<cv::Point2f>::type); k=0; for(int j=0;j <number_of_features;j++) { if(i == labels.at<int>(j)) { x.at<cv::Point2f>(k++) = samples.at<cv::Point2f>(i); } } printf("point values %f %f\n", x.at<cv::Point2f>(0).x,x.at<cv::Point2f>(0).y); cv::Size s=x.size(); printf("matrix size %d\n",s.height); cv::Moments m=cv::moments(x); printf("moments %f %f %f %f %f %f %f %f\n",m.m00,m.m01,m.m20,m.m11,m.m02,m.m30,m.m21,m.m03); double h[7]; cv::HuMoments(m,h); printf("moments %f %f %f %f %f %f %f\n",h[0],h[1],h[2],h[3],h[4],h[5],h[6]); ``` Strangely I cannot find any identical code sample from Google. All I see are C style approaches.

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