CODEWITHSUNDEEP
pythonopencv3dgeometry
Gsramati
Gsramati

Reputation: 93

Using 3D perception in opencv2

Can anyone please explain if it is possible, and if so how, to work with cv2.getPerspectiveTransform().

I have 3d information about my image: I know the length of a,b and also the Different heights of c,d,e,f and g. I made the height different to get more 3d information but if it isn't needed that will be preferable.

Ultimately I need to know where the pink dot really is in the rectangle after implementing the transform on my [x,y] position I get from the camera feed.

enter image description here

Upvotes: 2

Views: 599

Answers (1)

Camille
Camille

Reputation: 1690

If you denote by C,D,E,F the positions of the four corners of the black polygon in the original image (each of them is a 2D point), and C',D',E',F' the positions of the corresponding points in your target image (probably (0,0), (a, 0), (a, b), (0, b)), M = cv2.getPerspectiveTransform({C,D,E,F}, {C',D',E',F'}) is the perspective transformation from one polygon to the other.

Given the position G of the vertical projection of g onto the black polygon in the original image, you can compute its position in the target image as cv2.transform(G, M). This will return a point (x,y,z), where the last coordinate z is a normalizing term. This z is zero when your point would be "at infinity" in the target image. If z is not zero, the point you are looking for is (x/z, y/z).

If z is zero, your point is at infinity, in the direction of the support of vector (x, y) (think of the case where G would be at the intersection of the supporting lines of two opposite sides of the black polygon in the source image).

If you know that the heights of c,d,e,f,g are equal, these points are also coplanar, and the exact same method applies to c,d,e,f,g instead of C,D,E,F,G.

Upvotes: 1

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