The modified parameters in DRR Generator

There are some parameters which can be modified in DRR Generator. My understanding is that the “Rotation” of DRR Generator is to change the angle along the X, Y and Z axes, respectively. The “Translation” and the “Center” is the X/Y/Z distance from the emission source to the image. However, it seems that the “Translation” and the “Center” have the same function. Are these understandings right? How about the meaning of the “Focal Point” and “Direction”? Is there anyone else have been used DRR Generator before? I would appreciate getting your reply!