Extract centroids of connected components in EMGU - emgucv

Question

I have the following piece of code in EMGU to extract connected components:
Mat connected_array = new Mat();
Mat stats = new Mat();
Mat centroids = new Mat();
Mat ImgMat = new Mat();
CvInvoke.ConnectedComponentsWithStats(ImgThresh, connected_array, stats, centroids, LineType.EightConnected,DepthType.Cv32S);
I could not find any way to access the centroids.

Answer 1

EMGU wraps most arrays into Mat objects, which you then need to convert to arrays to access their contents (using mat.CopyTo(array)). This is not straight forward from the documentation - I've had to use trail & error to find out how it works:
Mat labels = new Mat();
Mat stats = new Mat();
Mat centroids = new Mat();
MCvPoint2D64f[] centroidPoints;
double x, y;
int n;
n = CvInvoke.ConnectedComponentsWithStats(image, labels, stats, centroids, LineType.EightConnected, DepthType.Cv32S);
centroidPoints = new MCvPoint2D64f[n];
centroids.CopyTo(centroidPoints);
foreach (MCvPoint2D64f point in centroidPoints)
{
x = point.X;
y = point.Y;
}
Another common method is to use Contours, similar functionality which EMGU also provides. I have used this for better performance. I include an example as well:
VectorOfVectorOfPoint contours = new VectorOfVectorOfPoint();
MCvMoments moments;
double area;
MCvPoint2D64f center;
int n;
CvInvoke.FindContours(image, contours, null, RetrType.External, ChainApproxMethod.ChainApproxSimple);
n = contours.Size;
for (int i = 0; i < n; i++)
{
area = CvInvoke.ContourArea(contours[i], false);
moments = CvInvoke.Moments(contours[i]);
center = moments.GravityCenter;
}