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Update rotatedRectangleIntersection function to calculate near to origin#19842

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Merged
alalek merged 6 commits intoopencv:3.4fromgasparitiago:3.4
Jun 12, 2021

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@gasparitiago
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@gasparitiagogasparitiago commentedApr 2, 2021•
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This commit changes the rotatedRectangleIntersection function in order to calculate the intersection of two rectangles considering that they are shifted near the coordinates origin (0, 0).

This commit solves the problem in some assertions from rotatedRectangleIntersection when dealing with rectangles far from origin.

Original issue:#19824

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    Patch to opencv_extra has the same branch name.
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@gasparitiagogasparitiago changed the titleIn the function that sets the points of a RotatedRect, the typesChange type used in points function from RotatedRectApr 2, 2021
In the function that sets the points of a RotatedRect, the typesshould be double in order to keep the precision when dealing withRotatedRects that are defined far from the origin.This commit solves the problem in some assertions fromrotatedRectangleIntersection when dealing with rectangles far fromorigin.
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crackwitz commentedApr 3, 2021•
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does this actually make a difference? it only applies double precision to the calculation itself but the result is still just FP32.

the demo code uses values like 4002326. there is simply not enough precision to go around (6-7 digits).

>>> [cx,cy,w,h,angle]=np.float32([246805.033  ,4002326.94   ,26.40587,6.20026,-62.10156])>>>_angle=angle*pi/180>>>a=np.sin(_angle)*0.5>>>b=np.cos(_angle)*0.5>>>f=np.float32;cx-f(a)*h-f(b)*w;cy+f(b)*h-f(a)*w246801.64002340.2>>>f=np.float64;cx-f(a)*h-f(b)*w;cy+f(b)*h-f(a)*w246801.593348281434002340.119037186

@gasparitiago
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@crackwitz

does this actually make a difference?

Yes. When testing the code provided by @jbwintergest here:#19824:

import cv2 as cvimport numpy as npdef box(box):    return ((box[0], box[1]), (box[2], box[3]), box[4])box_1 = np.array([ 246805.033  , 4002326.94   ,      26.40587,       6.20026,     -62.10156])box_2 = np.array([ 246805.122  , 4002326.59   ,      27.4821 ,       8.5361 ,     -56.33761])try:    print(cv.rotatedRectangleIntersection(box(box_1), box(box_2)))  # Assertion errorexcept Exception as e:    print(e)offset = (246805, 4002326, 0, 0, 0)box_1 -= offsetbox_2 -= offsetprint(cv.rotatedRectangleIntersection(box(box_1), box(box_2)))  # that works

when the functionrotatedRectangleIntersection, creates thepts1 andpts2 arrays and populate them, like this:

    Point2f pts1[4], pts2[4];    ...    rect1.points(pts1);    rect2.points(pts2);

This is the content ofrect1,rect2,pts1[0] andpts2[0] before and after this commit:

Before:

rect1.center.x246805.03125rect1.center.y4002327rect1.size.width26.405870437622070312rect1.size.height6.200260162353515625rect1.angle-62.101558685302734375rect2.center.x246805.125rect2.center.y4002326.5rect2.size.width27.482099533081054688rect2.size.height8.5361003875732421875rect2.angle-56.33760833740234375pts1[0].x pts1[0].y246801.59375 4002340pts2[0].x pts2[0].y246801.0625 4002340.25

After:

rect1.center.x246805.03125rect1.center.y4002327rect1.size.width26.405870437622070312rect1.size.height6.200260162353515625rect1.angle-62.101558685302734375rect2.center.x246805.125rect2.center.y4002326.5rect2.size.width27.482099533081054688rect2.size.height8.5361003875732421875rect2.angle-56.33760833740234375pts1[0].x pts1[0].y246801.59375 4002340.25pts2[0].x pts2[0].y246801.0625 4002340.25

When the functionrotatedRectangleIntersection code considers if two points are the same or not, points that are too far away from the origin (high x or y) are considered overlapped in thebefore code.

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the only difference between your two texts is that pts1[0].y is completely integer in the first and has a .25 decimal part in the second:

image

the algorithm itself will likely need fixes, not just theRect::points() method

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@asenyaev
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jenkins cn please retry a build

@vpisarev
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@gasparitiago, thank you for the contribution! I wonder if you could also modifyrotatedRectangleIntersection function to shift intersected rectangles closer to the coordinate origin (and then shift the intersection back)? This way we will get much more robust algorithm

@vpisarevvpisarev self-assigned thisJun 6, 2021
@gasparitiago
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Hello@vpisarev, I'm doing it. When I finish I will update this PR and let you know.

To be honest I will need some help on how to test the solution.

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@vpisarev can you take a look at my last commit?

This commit changes the rotatedRectangleIntersection function in orderto calculate the intersection of two rectangles considering that theyare shifted near the coordinates origin (0, 0).This commit solves the problem in some assertions fromrotatedRectangleIntersection when dealing with rectangles far fromorigin.
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Thank you for update!

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Looks good!
Please update PR's title and description before merge.

@gasparitiagogasparitiago changed the titleChange type used in points function from RotatedRectUpdate rotatedRectangleIntersection function to calculate near to originJun 8, 2021
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Thank you for contribution 👍

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@alalekalalek merged commit3cf4375 intoopencv:3.4Jun 12, 2021
@alalekalalek mentioned this pull requestJun 19, 2021
@alalekalalek mentioned this pull requestOct 15, 2021
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