Camera Calibration

Principal Point

The principle point is defined in the Calibration Matrix. It maps the intersection of Optical Axis with the image plane from an idealized projection. It defines the $(0,0)$ of the image plane.

• the point on the image plane onto which the perspective center is projected

Where is the principal point

The principal point is generally located around the center of the image plane from an idealized projection (not corrected).

I'm still not sure what the principal point is...

The principal point is basically a correction for the idealized projection. if you didn’t correct for it, you would end up with some negative image coordinates. However, the sensor sees only positive values, starting from (0,0). This correction that we are applying starts from the principal point.

This stackoverflow thread helped me be less confused.

More

• https://stackoverflow.com/questions/50421178/camera-projection-matrix-principal-point
• https://www.baeldung.com/cs/focal-length-intrinsic-camera-parameters
• https://stackoverflow.com/questions/6658258/principle-point-in-camera-matrix-programming-issue

• https://docs.opencv.org/2.4/modules/calib3d/doc/camera_calibration_and_3d_reconstruction.html