camera rotation and translation based on two images

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Hello,

I'm just starting my little project in OpenCV and I need your help :) I would like to calculate rotation and translation values of the camera basing on two views of the same planar, square object.

I have already found functions such as: getPerspectiveTransform, decomposeEssentialMat, decomposeHomographyMat. Plenty of tools, but I'm not sure which of them to use in my case.

I have a square object of known real-world dimensions [meters]. After simple image processing I can extract pixel values of the vertices and the center of the square.

Now I would like to calculate the relative rotation and translation of the camera which led to obtain the second of two images:
"Reference view" and "View #n"
(please see below).

Any suggestions will be appreciated :)

1. Reference view:
   
   (center of the object is on the optical axis of camera, the camera-object distance is known)
2. View #1:
   
3. View #2:
   
4. View #3: