This document provides an overview of 2D and 3D air-based projection systems called Heliodisplays. It discusses the working principle of Heliodisplays, which use frustrated total internal reflection to project images into thin air without a physical screen. The document outlines the history and types of Heliodisplay models, and describes their applications in areas like advertising, video conferencing, and military training. Advantages are noted as the ability to project images without affecting air quality or requiring glasses, though disadvantages include high cost and image distortion in moving air.