A pattern able to be updated by an operator, the position, the orientation and/or the shape of the trajectory pattern dependent on trajectory parameters, the device comprises at least display means to view the trajectory pattern and the representation of the zone, and means for computing and storing the position data of the pattern and of the representation, the representation comprising a set of control points, the function of a control point being to define at least the value of one of the trajectory parameters, the value being dependent on the movement of the control point, a trajectory pattern modification resulting from an interaction of the operator moving at least one control point.