rectA & rectB not working

LineIntersection

asked 2016-12-23 01:36:30 -0600

Nbb
731 ●12 ●23 ●38

updated 2016-12-23 02:37:13 -0600

I am trying to get the intersection of 2 rectangles. What happens if the 2 rectangles do not intersect at all ? Will it give me an error ? Because the output below is what I am getting. The limits are (0,0,1242,375). I don't know the rectangles I am passing in. I just want to keep those that intersect and to retain the intersection.

[1170 x 232 from (72, 0)]
[1242 x 375 from (0, 0)]
[1242 x 375 from (0, 0)]
[967 x 211 from (275, 0)]
[1242 x 375 from (0, 0)]
[1242 x 375 from (0, 0)]
[1242 x 375 from (0, 0)]
[2147449647 x 375 from (2147483647, 0)]
[1242 x 375 from (0, 0)]

I am using this temporary fix after the intersection operator to remove all erroneous rectangles

if (rect.tl().x < 0 || rect.tl().y < 0 || rect.br().x >= image.cols || rect.br().y >= image.rows 
                                || rect.area() >= image.cols * image.rows || rect.area() == 0)

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2147483647 == 0x7fffffff == INT_MAX.

looks like you have a bug elsewhere ...

berak ( 2016-12-23 01:47:06 -0600 )edit

thanks ! but wouldn't int_max be reduced to 1242 due to the intersection ? should I introduce another check for INT_MAX ? I am projecting 3D bounding boxes onto a 2D image so I guess if the box lies outside of the image then something weird might happen. I had hoped that the intersection would be enough

Nbb ( 2016-12-23 01:55:49 -0600 )edit

~~"should I introduce another check for INT_MAX" -- no, no, rather be paranoid about the rest of your program(linked wrong libs again ? buffer overflow somewhere ? uninitialized meory ?)~~

berak ( 2016-12-23 02:00:09 -0600 )edit

I think the error just lies at the projection function, if a corner of the 3D bounding box is "on the image plane" then its projection will be at infinity

Nbb ( 2016-12-23 02:05:27 -0600 )edit

oooh, that again sounds pretty likely ! (in that case, forget all remarks above.)

berak ( 2016-12-23 02:07:39 -0600 )edit

is there a solution ? Why doesn't it work for INT_MAX ? isn't that still a number ? Im currently using the area to filter out such rectangles rect.area() < image.rows*image.cols but im afraid if there are other rectangles that just lie out of bounds but still remain below the maximum area since it looks like the intersection operator doesn't work as I had hoped it would

Nbb ( 2016-12-23 02:16:37 -0600 )edit

code source for rect intersection is here. INT_MAX+width is not possible

LBerger ( 2016-12-23 02:57:25 -0600 )edit

you can't use area() to filter those out, since INT_MAX * something is already over the top. (or say INT_MAX + anything)

berak ( 2016-12-23 03:09:01 -0600 )edit

if a corner of the 3D bounding box is "on the image plane" I understand a field of view problem using a stenope model...

LBerger ( 2016-12-23 03:14:58 -0600 )edit

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answered 2016-12-25 07:53:54 -0600

essamzaky
583 ●2 ●5 ●18

updated 2016-12-26 08:26:38 -0600

you can do the following checking to detect if there is intersection between the two rectangles or not

BOOL IsOverLap(RECT A, RECT B)
{
    //return true if there is overlapping between the two rectangles
    return ! (A.top > B.bottom || A.bottom < B.top || A.left > B.right || A.right < B.left);
}

Edit 26/12/2016

And here it is the implemetation by using cv::Rect

BOOL IsOverLapCV(Rect A, Rect B)
{
    //return true if there is overlapping between the two rectangles
    return ! (A.y > (B.y + B.height) || (A.y + A.height) < B.y || A.x > (B.x + B.width) || (A.x + A.width) < B.x);
}

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i like your idea, but you're confusing cv::Rect and the RECT from win32 api above.

berak ( 2016-12-25 08:11:22 -0600 )edit

Yes ,it's confusing , he can use OpenCV cv::Rect , i just copied function from my code

essamzaky ( 2016-12-25 09:38:49 -0600 )edit

The original issue was that one of the dimension of the rectangle was INT_MAX and thus there is an overflow in the check.

There are two solutions in my opinion:

solve / check the issue with the projection on the image plane
promote the int type to a bigger type (float or double)

Eduardo ( 2016-12-26 15:55:54 -0600 )edit

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