The 180˚ Rule
The 180˚ Rule is one of the most fundamental elements of filmmaking. Establishing the orientation of the audience. Two actors or objects in the same scene must always have the same relationship to each other based on an imaginary straight line passing on an axis through them. The camera may not pass over the same virtual line that passes through the two subjects. The camera should be positioned anywhere on this 180 arc, i.e. on one half of the virtual axis. In this way a clear relationship is established between actors or objects in the scene. If the 180 rule is not followed this is called "crossing the line" which may lead to the disorientation of the viewer. This can be used as a deliberate technique.