This component has no physical size (like Arm - also drawn that
way), but is used to set the polarisation in one of two ways:
1) (randomOn=0) Hardcode the polarisation to the vector (px, py, pz)
2) (randomOn!=0) Set the polarisation to a random vector on the unit sphere
Example: Set_pol(px=0, py=-1, pz=0)
Parameters in boldface are required;
the others are optional.