OAK-FFC4P Calibration

Tjjl

I want to ask, when using calibrate.py to calibrate the FFC-4P, if a JSON file generated by a 9298 grayscale camera with a resolution of 1280X800 is used, I found that there is a significant error when using the camera parameters and distortion coefficients from this file to calibrate images from a 400P camera. How can this be resolved, or how can the resolution of the JSON file generated during calibration be set to 400P?

Thanks

jakaskerl

Hi @Tjjl
The intrinsics change in the back when using a lower resolution. If you want to manually specify the new intrinsics at a lower (different resolution) you can use https://docs.luxonis.com/projects/api/en/latest/references/python/?highlight=getcameraintrinsics#depthai.CalibrationHandler.getCameraIntrinsics.

Thanks,
Jaka

Tjjl

Jaka

Thank you for your assistance. I have resolved the issue.

I have another question to consult. When I use the code depthBC->disparity.link(depthBCOut->input) to obtain depth information, I want to convert this type of data into actual depth values. I use the code BCMat.at<uchar>(stay, stax) to read the disparity value of depthBC, and then I use the formula from this link: Configuring Stereo Depth to calculate the depth. We are using a focal length $��$fx of 441.25 corresponding to 400p. However, the calculated depth is approximately twice the actual depth.

Thank you!

jakaskerl

Hi @Tjjl
What values are you putting in and what is your disparity range (eg. are you using extended disparity)?

Thanks,
Jaka

Tjjl

jakaskerl

We created a mono node, and in the code "BCMat.at<uchar>(stay, stax)", 'stay' and 'stax' represent the y and x coordinates of the input image respectively. We did not use any extensions. Our experiment showed a distance of 115cm, whereas the actual measured distance is 70cm.

Thank you.

Tjjl

jakaskerl
Sorry, Jaka, I seem to have found the problem. The 'fx' in the formula should be the one obtained from actual measurements, right? I've corrected it, and the accuracy has greatly improved.

Thanks

jakaskerl

Hi @Tjjl
Should be retrievable from calibration.

To get focal length in pixels, you can read camera calibration, as focal length in pixels is written in camera intrinsics (intrinsics[0][0])

Thanks
Jaka