VIEWING VOLUME

The 3D space is defined by 3 axis (vectors) : X, Y and Z. These 3 axis creates an axis system (see Tutorial 4for a representation of this axis system). All points of the 3D space can be expressed as a linear combination of these vectors. A point is point represented by its coordinates (x, y, z), which means x * X + y * Y + z * Z (upper case is a vector, low case is a scalar). The volume of the entire 3D space is infinity.

The Viewing Volume delimites the 3D space by creating a closed volume. Points outside this volume will not appears on the screen.
This particularity explain the first call glTranslate (just after glLoadIdentity) : we go inside the Viewing Volume. At start, we are on the front plane of the viewing volume.

The Viewing Volume can be created with two different kind of projections :
    Perspective Projection  Render object affected by the distance, a car is seen smaller when it move away.
    Orthographic Projection Render object NOT affected by the distance like a menu, a text on the screen, 2D objects ...