An apparatus comprising an electromagnetic radiation source communicably coupled to a control system and a three dimensional (3D) image projector for outputting a plurality of image signals representative of a subject, the control system being configured to cause electromagnetic radiation to be applied to a plurality of sets of selected three-dimensional portions of a gaseous volume so as to heat and/or ionize the gas within selected portions, wherein each set of selected three-dimensional portions of gaseous volume intersects a path of a respective one of image signals, and wherein selected portions of each of set are spatially located together in a substantially unbroken three-dimensional configuration and selectable orientated and configured to simulate an electromagnetic radiation path modifying element for directing a respective image signals incident thereon to a selected location within a viewing region.