Calibration Issue: Poor Depth & High Reprojection Error on Virtual Stereo ZED X One

Hardware ZED1
,
1

Hi,
I’m facing a calibration problem with a Virtual Stereo setup made of two DUAL ZED X One cameras connected to a ZED Box. I created the virtual stereo, then attempted calibration using the ZED Calibration Tool.

Problem

After calibration, when I visualize the depth on ZED Depth Viewer, the results are very poor (unstable / inaccurate).
Looking at the calibration report, I always get a high reprojection error, even when following the recommended steps.

Here are some examples:

  • Best attempt so far:

    Reprojection error: Left 0.927619 | Right 0.633618 | Stereo 0.875887
!! Warning !!
The reprojection error looks too high, check that the lens are clean (sharp images) and that the pattern is printed/mounted on a strong and flat surface.

  • Worst attempts reach above 2.0 error on Left lens.

What I already tried

  • Lenses are clean and image sharpness looks good.

  • Tried multiple calibration patterns:

    • 9x6, square size 22 mm (A4)

    • 9x6, square size 34 mm (A3)

    • 10x7, square size 22 mm (A4)

  • Patterns printed and mounted on a flat and rigid surface.

  • Calibration consistently gives a correct baseline.

Questions

  • Is there a known issue or extra step when calibrating a Virtual Stereo ZED X One setup?

  • Do the ZED X One lenses require a specific pattern size or board distance range to achieve <0.5 reprojection error?

  • Any tips to achieve a better calibration?

Any guidance would be highly appreciated.

Thanks!

2

Hi @byarbi
Welcome to the Stereolabs community.

I recommend you try to calibrate the cameras using the new Calibration tool that will be launched in a few days:

It uses the new Virtual Stereo API functions of the ZED SDK v5.1 to open the cameras in a virtual stereo setup.

The new calibration tool uses different methods to guarantee that the saved images create a valid database to generate a good calibration by checking the checkerboard position, orientation, and size.

You can use the command ZED_Opencv_Calibration -h to get all the parameters.

Normally, you can start a calibration by using the simple command
ZED_Opencv_Calibration --zedxone --left_id 0 --right_id 1

I recommend you use ZED_Explorer --all or ZED_Studio to by sure that the left camera has index 0 and the right camera has index 1.