Get Oak-D focal length

i2sCV

Hello,

I am getting an image from the RGB central camera and the corresponding depth from the left/right cameras.
Using that I am calculating some distances on the RGB image (in pixels) and I would like to convert that pixel distance to actual (world) distance using the depth information.
To do that, I am trying to get the focal length of the OAK-D camera.
I have the following questions:

Where can I find the focal length of the camera? I looked at all the documentation and it is not mentioned anywhere.
Does the focal length change when the camera focuses with the auto-focus? If so how can I get the focal length for each frame dynamically when capturing the images?

Any help you can offer will be much appreciated.

erik

Hello i2sCV , you can get focal point from camera intrinsic, demo here - focaLen = camIntrinsics[0][0].
For the second question; I am actually not sure, will ask the team internally about it.
Thanks, Erik

i2sCV

Dear Erik,

Thank you very much for the reply.
I found the focal length using the code you provided and converted the focal length given by the intrinsic matrix to the focal length in mm using the formula focal_length_mm = focaLen * (6.17mm (sensor width) / 4056 (pixel width of sensor).
Please let me know when you have any news regarding the autofocus and focal length issue.
Thank you very much for your help!

erik

Hello i2sCV , here's the response I got from the team:

There is a slight FOV change (and so a focal length change) depending on the lens position, but I think we haven't characterized it yet.
It would be useful to have, also for RGB-depth alignment, recalculating the warp transform matrix when the lens position changed.