The MAster Reference System ( MARS)

The kinematic variables of the particles transporter by GEANT are always referred to the so-called MAster Reference System ( MARS). This system is implicitly defined as the local reference system of the first volume defined, which contains all the others. This is a Cartesian coordinate system with axis $x,y,z$ where $z=xxy$ . If the axes are labelled (X,Y,Z), then the point P is represented in fig .

Figure: GEANT reference system

Tracking is performed in the MARS and the input position for user routines such as the magnetic field routine is given in this system.