如何从 KITTI 数据集计算相机的焦距

Question

I work on the Kitti dataset of stereo images. I have the intrinsic matrix given:

K_l = np.array([9.597910e+02, 0.000000e+00, 6.960217e+02, 0.000000e+00,
                9.569251e+02, 2.241806e+02, 0.000000e+00, 0.000000e+00, 1.000000e+00])

How can I compute the focal length from this matrix?

We know that this matrix has the expression:

cam.K =     [ -f/d   0    Cx;
                0  -f/d   Cy;
                0    0     1];

Thanks.

Answer 1

In the camera matrix f is normally expressed in pixels, so you must multiply it by a coefficient to retrieve real world coordinates:

Fx = fx * W / w

with:

• W: sensor width in world coordinates (meters)
• w: sensor width in pixels (number of pixels in a row)

Those informations are available on the camera specs.