Add rectangles to a trapezoid openCV C++

Question

I have an image with two areas. I want to add now rectangles with a fixed size randomly into area2. The coordinate origin of the image is in the top-left corner. I have the cordinates of the area2. This are P1, P2, P3(0, y_max) and P4(x_max, y_max). Does anybody knows how to check, if a rectangle lies in this area? I can try to separate this area into 2 parts, a rectangle (rect_area) and a triangle (trangle_area). For the rect_area I can check with

bool intersects = ((rect_area & rect_random).area() > 0); if the random rect lies inside the area. For the triangle I have found some complicated stuff like here: How to determine if a point is in a 2D triangle?

Does anybody knows an easier way to do that?

Stove · Accepted Answer · 2019-01-05T13:32:58.837

1

Does the graph you draw represent the general case of the problem?

P1.x == 0
P2.x == 0
q1.x == q2.x
q2.y == q3.y

If the above conditions hold, then you can check

if q1 is below the line of P1P2 (q1.y > (q1.x*(p2.y-p1.y)/x_max)+p1.y)
q2 is abovep2 (q2.y < P2.y)

edited Jan 05 '19 at 13:32

answered Jan 04 '19 at 15:57

Stove

116
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P2.x > 0. How can I check, if q1 is above or below Line P1P2? – HanzDieter Jan 04 '19 at 16:18
you can check q1.y > (q1.x*(p2.y-p1.y)/x_max)+p1.x – Stove Jan 04 '19 at 16:26
I don´t see it right now. Can you explain the equation, please? – HanzDieter Jan 04 '19 at 16:42
I made a typo, it should be q1.y > (q1.x*(p2.y-p1.y)/x_max)+p1.y – Stove Jan 04 '19 at 16:47
(p2.y-p1.y)/x_max is the slope (dy/dx) of the line, p1.y is the offset. it is y coordinate of line at q.x is given by q.x*(slope of line) + (offset of line) – Stove Jan 04 '19 at 16:49

Add rectangles to a trapezoid openCV C++

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