PERSPECTIVE PROJECTION

With this kind of projection, the viewing volume shape is a truncated pyramid (its top is cutted).

This shape is abtained by 6 cutting planes : front, back, right, left, top and bottom planes (planes at the volume boundary). These planes are commonly called Clipping Planes. These planes can be created with the aid of the method :
    glu.gluPerspective(fovy, aspect, near, far)
The fovy parameter is the angle between the plane that goes downwards and the plane that goes upwards.
The aspect ratio is generaly the aspect ratio of the window (window is the region of the screen in which the scene is rendered).