ZED X One S Stereo Calibration Fails at 0.5 m Baseline

NivC · March 31, 2026, 12:14pm

I’m trying to calibrate a custom stereo setup using two ZED X One S (narrow FOV), but calibration fails due to high reprojection errors even at a relatively short baseline of 0.5m.

My Setup:
Cameras: 2 × ZED X One S (narrow)
Mounting: Rigidly fixed on a static bar (no movement)
Current baseline tested: 1 m and 0.5 m
Future goal: ~2 m baseline

Calibration pattern:
Chessboard: 11 × 8 inner corners
Square size: 65.3 mm
Printed and mounted on a rigid flat surface

Followed the official guide:
https://www.stereolabs.com/docs/cameras/zed-x-one/zed-x-one-stereo
Achieved 100% coverage in all metrics: X,Y,Size,Skew.

Calibration fails due to reprojection error:

Even when coverage is perfect, I cannot get below the 0.5 px threshold, although i am very close to success, there is always something that above 0.5 and fails me.

This happens at 0.5 m baseline, not long baseline

Observations

This happens at 0.5 m baseline, not long baseline
Cameras are completely rigid
Chessboard is flat and stable
Images look sharp and well exposed
Repeating calibration gives slightly different results, but always above threshold

Eventually I want to calibrate a ~2 m baseline stereo rig, so I’m trying to validate the process first at 0.5 m. what size of square i will need at this case if i cannot handle the 0.5 m ?

Myzhar · March 31, 2026, 5:39pm

You could try to use bigger squares (80 mm) to improve the detection when the target is moved far from the cameras.
Also, check that there are no flares and shadows on the target.

You are not too far from the threshold (0.5 px), it’s only a matter of a few steps:

github.com/stereolabs/zed-opencv-calibration

stereo_calibration/src/main.cpp

main


      
          void applyCoverageIndicatorOverlay(cv::Mat& image,
                                             const cv::Mat& coverage_indicator,
                                             const cv::Mat& limits_indicator);
          void applyPosIndicatorOverlay(cv::Mat& image, const cv::Mat& pos_indicator);
          
          /// Rendering
          constexpr int text_area_height = 380;   // Height of the area below the images
          const cv::Size display_size(720, 404);  // Size of the rendered images
          
          /// Calibration condition
          const float max_repr_error = 0.5;  // in pixels
          const int min_samples = 25;
          const int max_samples = 35;
          const float min_avg_x_coverage =
              0.65f;  // Checkerboard X position covering percentage of the image width
          const float min_avg_y_coverage =
              0.65f;  // Checkerboard Y position covering percentage of the image height
          const float min_area_range =
              0.4f;  // Checkerboard area range size [min_area-max_area]
          const float min_skew_range =
              0.375f;  // Checkerboard skew ange size [min_skew-max_skew]