Final answer:
The center of rotation must be determined for each collimator used, each matrix used, and each zoom factor used.
Step-by-step explanation:
The center of rotation must be determined for each collimator used, each matrix used, and each zoom factor used. In rotation, these factors are essential in understanding the position and orientation of the objects being rotated. For example, in the case of a collimator, the center of rotation would determine the axis of rotation for the collimator, which is crucial for its proper functioning.