The 3D projection is a linear projection of the data such that a given axis is transformed into a stright horizontal line through the center of the window. It allows the user to perform rotations about an arbitrary axis in space. The unit vector of this axis is defined by (xAxis, yAxis, zAxis). The center of rotation is taken to be the reconstructed primary vertex of the event.
Rotations about the selected axis by an angle φ are performed by dragging with the R modifier key pressed down in the ZMR interaction (see 4.1 Zoom/Move/Rotate (ZMR)).
The axis of rotation will by default be set to the line joining the primary vertex to the last secondary vertex to be reconstructed.