SFM module input parameters

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Hi, I have just started experimenting with the SFM module, and I had a question, how would we obtain the input parameters, namely the focal length f, and the center of projection coordinates cx and cy?

I understand that the focal length can be obtained after doing a camera calibration in OpenCV, thus getting back focal lengths fx and fy, as well as the optical centres cx and cy in pixel coordinates (what do we do if fx and fy are not equal?). Are these the same that we need to pass on to the SFM functions, as described in the following tutorial? :

http://docs.opencv.org/3.1.0/d5/dab/t...

Thanks!