Why is there a difference in camera parameters between the ZED SDK API and the ZED Explorer tool?

The ZED Explorer tool displays the camera's raw color stream, without rectifying the frames to correct the distortions caused by the optics. The camera parameters in the "Calibration" tab of the settings window refer to these raw, unrectified frames.

When you use the ZED SDK API to retrieve the VIEW::LEFT and VIEW::RIGHT color images, you get the rectified images used by the ZED SDK processing pipeline to compute depth. The corresponding calibration parameters are:

C++:

sl::CalibrationParameters calibration_params = zed.getCameraInformation().camera_configuration.calibration_parameters;

Python:

calibration_params = zed.get_camera_information().camera_configuration.calibration_parameters

These parameters are different from the parameters displayed by ZED Explorer:

1. the left and right intrinsic parameters are the same, because the rectified images have their epipolar lines aligned on the same rows (see Epipolar geometry for details);

2. the distortion parameters are zero, because the images are rectified and the distortions are removed.

To obtain the raw parameters of the VIEW::LEFT_UNRECTIFIED and VIEW::RIGHT_UNRECTIFIED images, use:

C++:

sl::CalibrationParameters calibration_params_raw = zed.getCameraInformation().camera_configuration.calibration_parameters_raw;

Python:

calibration_params_raw = zed.get_camera_information().camera_configuration.calibration_parameters_raw

Even comparing calibration_params_raw with the parameters shown by ZED Explorer, you may notice small differences. They are caused by the self-calibration of the ZED SDK: when the camera is opened with open(), the ZED SDK runs a quick self-calibration to compensate for small variations of the optics caused by temperature changes, vibrations, and small shocks.

You can disable this behavior by setting camera_disable_self_calib to true in InitParameters.

For more information, see Camera Calibration in the ZED SDK documentation.