Now that you have a view of the physical world on your screen, our next goal is to overlay digital 3D models on top of it. Overlay in 3D as used in Augmented Reality, is different from basic 2D overlays possible with Adobe Photoshop or similar drawing applications (in which we only adjust the position of two 2D layers). The notion of 3D overlay involves the management and rendering of content with six degrees of freedom (translation and rotation in three dimensions) as shown in the following figure:
In this chapter, we will guide you through the different concepts and present you with the best way to superimpose real and virtual content. We will successively describe the concept of real and virtual cameras, how to perform superimposition with our scene graph engine, and create high quality superimposition. First, let's discuss the 3D world and the virtual camera.