Hi， I have a question about the Principle Point and the cx、cy in intrinsic matrix K. first, let me have a description about my application scenarios. Look at the figure 1 bellow, the camera Z axis ( Optical axis ) point to the Top, so it can rotate 360 degree along the Z axis. In this case, the corners in image that corresponding to the same world point (homonymy point) should be on the circle path centered at Principle Point in image coordinate frame. After calibration, I take two images, Look at the figure 2 bellow, before(X1 axis) and after(X2 axis) rotating 180 degree, with Z axis point to the Top, that is Optical axis is perpendicular to the ceiling. In this case, the image will be rotate 180 degree about the Principle point.

Through finding the homonymy point , we can find the true Principle Point. it can be compared with the cx, cy in intrinsic matrix K.

The coordinate of pixel 1 is (u1,v1), pixel 2 is (u2,v2), so, the true Principle Point is {(u1+u2)/2, (v1+v2)/2}. We will find the offset of principle point after Calibration with it compared with the cx, cy in intrinsic matrix K.

Here is one of my results：

P1: 484 557

P2: 385 183

Mean of p1、p2：434.5 370

Cx\cy in K：434.1 362.2

So，this phenomenon confused me!，can u give some advice？