CODEWITHSUNDEEP
camerafieldofviewkitti
vrk-prgmr
vrk-prgmr

Reputation: 1

How to calculate the Horizontal and Vertical FOV for the KITTI cameras from the camera intrinsic matrix?

I would like to calculate the Horizontal and Vertical field of view from the camera intrinsic matrix for the cameras used in the KITTI dataset. The reason I need the Field of view is to convert a depth map into 3D point clouds.

Upvotes: 0

Views: 1713

Answers (1)

Frank Castle
Frank Castle

Reputation: 33

Though this question has been asked quite a long time ago, I felt it needed an answer as I ran into the same issue and was unable to find any info on it.

I have however solved it using the information available in this document and some more general camera calibration documents

Firstly, we need to convert the supplied disparity into distance. This can be done through fist converting the disp map into floats through the method in the dev_kit where they state:

disp(u,v) = ((float)I(u,v))/256.0;

This disparity can then be converted into a distance through the default stereo vision equation:

Depth = Baseline * focal length/ Disparity

Now come some tricky parts. I searched high and low for the focal length and was unable to find it in documentation. I realised just now when writing that the baseline is documented in the aforementioned source however from section IV.B we can see that it can be found in P(i)rect indirectly.

The P_rects can be found in the calibration files and will be used for both calculating the baseline and the translation from uv in the image to xyz in the real world.

The steps are as follows:

For pixel in depthmap:

xyz_normalised = P_rect \ [u,v,1]

where u and v are the x and y coordinates of the pixel respectively

which will give you a xyz_normalised of shape [x,y,z,0] with z = 1 You can then multiply it with the depth that is given at that pixel to result in a xyz coordinate.

For completeness, as P_rect is the depth map here, you need to use P_3 from the cam_cam calibration txt files to get the baseline (as it contains the baseline between the colour cameras) and the P_2 belongs to the left camera which is used as a reference for occ_0 files.

Upvotes: 0

Related Questions