Most packaging vision verifies rather than steers. Guidance shows up where a part is free to rotate or translate: an angle passed to a rotary gripper, or a fiducial offset for a gantry. The camera must report a calibrated world pose, not a pixel pose with a hopeful scale factor.
Calibration should be checked with a certified reference at more than one point in the region, because a single scale constant hides perspective and distortion. Linearity, uniform illumination, and controlled height are the hardware preconditions. If the pattern used for the pose is retrained, the old position and angle have to be reconciled with the new model’s zero-angle train pose. A guidance job tested only at the center of the field will pass buyoff and miss at the edges, which is where free parts actually land.