HORIZON LINE (HL): The horizon line is the position of the horizon that
may or may not be visible on the picture plane depending on your angle of
sight. The horizon line is also known as the eye level. Eye level is typically
defined as 5 feet 6 inches above the ground.
GROUND LINE (GL): The ground line represents the edge of the ground
plane on which the object rests. The ground line defines the lower limits of
Figure 5-8 illustrates component parts of the principles of perspective.
Figure 5-8.Component parts in perspective.