How can one easily detect whether 2 ROIs intersects in OpenCv?

Question

I am trying to detect whether 2 Regions of Interest (CvRects) are intersecting one another in OpenCV. I can obviously manually type several (or rather a lot of) conditions to be checked but that wouldn't really be a good way to do it (imo).

Can anyone suggest me any other solution? Is there a ready method in OpenCV for that ?

Answer 1

I do not know of any ready-made solution for the C interface (CvRect), but if you use the C++ way (cv::Rect), you can easily say

interesect  = r1 & r2;

The complete list of operations on rectangles is

// In addition to the class members, the following operations 
// on rectangles are implemented:

// (shifting a rectangle by a certain offset)
// (expanding or shrinking a rectangle by a certain amount)
rect += point, rect -= point, rect += size, rect -= size (augmenting operations)
rect = rect1 & rect2 (rectangle intersection)
rect = rect1 | rect2 (minimum area rectangle containing rect2 and rect3 )
rect &= rect1, rect |= rect1 (and the corresponding augmenting operations)
rect == rect1, rect != rect1 (rectangle comparison)

Answer 2

bool cv::overlapRoi(Point tl1, Point tl2, Size sz1, Size sz2, Rect &roi)
{
    int x_tl = max(tl1.x, tl2.x);
    int y_tl = max(tl1.y, tl2.y);
    int x_br = min(tl1.x + sz1.width, tl2.x + sz2.width);
    int y_br = min(tl1.y + sz1.height, tl2.y + sz2.height);
    if (x_tl < x_br && y_tl < y_br)
    {
        roi = Rect(x_tl, y_tl, x_br - x_tl, y_br - y_tl);
        return true;
    }
    return false;
}

Yes. There is a ready method in OpenCV for that in opencv/modules/stitching/src/util.cpp