Define an origin on stage (coordinate system on stage)
Note: zactrack uses a right handed cartesian coordinate system.
X+ and Y+ axis are located on the floor and Z+ axis looks into the ceiling.
The origin can be chosen freely anywhere on stage. It is recommended to align the X or Y axes parallel to the stage. Usually downstage center is a common origin with an X+ axis orientation towards stage right parallel to the stage. Y+ axis looks upstage and Z-axis looks into the ceiling.