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Projection matrix

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Hi Can anyone help me in getting the rotation matrix and translation vector out of a projection matrix? Here's an example matrix: -0.0137766 -0.000755008 -0.000706549 -2.162e-07 -0.0011148 -0.0140701 3.79405e-05 7.68527e-09 -5.30034e-06 -6.65135e-06 -1.84527e-05 8.2956e-06 Also, is it possible to extract the focal length or field of view from this? Help very much appreciated!! Ben

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What exactly are you trying to do? A projection matrix contains information about dimension reduction. Typically, we're concerned with displaying 3d geometry on a 2d screen. In any case, it doesn't have much to say about rotation or translation. You can certainly get field of view or other projection-related info out of such a matrix, though.

The matrix you posted is a 3x4 matrix, which suggests that it's an affine transformation or perhaps an orthogonal projection using column vectors. The entries are very small though, and the form is not immediately recognizable, to me at least. Where'd you get it? Is it a concatenation of several transformations including projection?

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Thanks for the reply.

I believe it is the intrinsic camera parameters and the modelview. It is camera calibration information, from camera footage. I have up until this point been provided with focal length, principal point, fov, trans, rot, etc. But now with this new software I can only get this single matrix, which I am told is the "projection matrix" containing camera params and world positioning.

Thanks!

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Quote:
It is camera calibration information, from camera footage.
This isn't something I'm familiar with, so I'm afraid I can't be of further help. But given the additional information you've provided, perhaps someone else will be able to point you in the right direction...

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It sounds like hes talking about the camera.projectionMatrix and viewMatrix in the sampleFramework were any Matrix operation effects the viewMatrix.

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hi!

I think you could do a QR factorization of the projection matrix you have:
QR = P
Then look at the entries in Q at Q(1,1) and Q(2,2).
Those should contain the focal length expressed in horizontal and vertical pixel units respectively. If you divide these two you get the aspect ratio. Usually the aspect ratio is 1. Or its a good approximation for many ordinary cameras I think.

Let me know if this helped you :)
Note: im not sure this is the right way to do it in your case, but i am confident enough to reply :-D

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