DATA INPUT DEVICE FOR COMPUTERS, NAMELY, A DEVICE UTILIZING AT LEAST ONE JOYSTICK FOR CONTROLLING THE POSITION AND ORIENTATION OF A DATA SET EFFECTIVELY BY THE USER'S HAND AND SPECIFICALLY FOR EXPLORING VOLUMETRIC DATA SETS FROM DIFFERENT DOMAINS AND, MORE SPECIFICALLY, TO POSITION THREE ORTHOGONAL SLICES IN VOLUMETRIC DATA SETS OR THREE ORTHOGONAL CLIPPING PLANES IN POLYGONAL DATA SETS