How to select the contour bounding a point (mouse event)

asked 2016-10-07 16:45:04 -0600

yannb
6 ●2

Hello everyone.

I am working with OpenCV and I need to do the following :

I have a contours vector, built with cv::findContours. I need to click the picture, select the first contour bounding the click-point, and draw it on the picture.

But I don't know a good way to select in the contours vector the first contour bounding a point. Could you help me on this, please ?

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answered 2016-10-07 23:41:48 -0600

berak
32993 ●7 ●81 ●312

updated 2016-10-08 03:18:30 -0600

opencv has pointPolygonTest for this:

Point mouse(x,y); // picked point
int hitId = -1; // id of picked contour

for (size_t i=0; i<contours.size(); i++) {
     if (pointPolygonTest(contours[i], mouse,false) > 0) {
         hitId = i;
         break;
    }
}
// now, you still might end up with hitId == -1
// there will be the case, where you did **not** hit any contour, take care !