How to verify that the camera calibration is correct? (or how to estimate the error of reprojection)

Question

The quality of calibration is measured by the reprojection error (is there an alternative?), which requires a knowledge world coordinates of some 3d point(s).

Is the

Answer 1

To calibrate the camera one has to jointly solve for extrinsic and intrinsic. The latter can be known from manufacturer, the solving for extrinsic (rotation and translation) involves decomposition of calculated homography: Decompose Homography matrix in opencv python

Calculate a Homography with only Translation, Rotation and Scale in Opencv

The homography is used here since most calibration targets are flat.