What are the focal lengths and the principal point in KITTI stereo dataset?

Question

I am using the KITTI stereo dataset 2012 and 2015 in a research.

But I need some values that I didn't find:

1. focal lengths for x and y direction.
2. the principal point.

There are some files inside the "calib" folder in dataset. A content example is here (calib/000000.txt):

P0:
707.0912   0.     601.8873    0.
  0.     707.0912 183.1104    0.
  0.       0.       1.        0.

P1:
707.0912   0.     601.8873 -379.8145
  0.     707.0912 183.1104    0.
  0.       0.       1.        0.

P2:
707.0912   0.     601.8873   46.88783
  0.     707.0912 183.1104     .1178601
  0.       0.       1.         .006203223

P3:
707.0912   0.     601.8873 -333.4597
  0.     707.0912 183.1104    1.930130
  0.       0.       1.         .003318498

Following this paper (specifically in section IV, B): http://www.mrt.kit.edu/z/publ/download/2013/GeigerAl2013IJRR.pdf

I got that P is the projection matrix after retification. And i ∈ {0, 1, 2, 3} is the camera index, where 0 represents the left grayscale, 1 the right grayscale, 2 the left color and 3 the right color camera.

But my problem is that I don't know how to find the focal length and the principal point that I need.

Can someone help me?

Thank you all!

Answer 1

The P0 matrix is the projection matrix.

Value at P0[0, 0] is Fy, the focal length along the x axis,

P0[0, 2] is Cx,

P0[1, 1] is Fy, and

P0[1, 2] is Cy.

The P0 matrix is like any other projection matrix.