As the cans rise above the horizon line, you can see their bottoms. Below the horizon line, you see their tops. In the middle you see neither.
Look at the illustration of the soda cans. You'll notice several cans drawn one above another. In the middle is a line, known as the horizon line. This illustrates one of the two basic principles of perspective.
As an object moves vertically, its relation to the horizon line determines how it is drawn. The horizon line can also be thought of as the viewer's eye level. As the cans rise above the eye level, the viewer sees the bottoms of the cans. As the cans sink below eye level, the viewer sees the tops. As the center of the can lines up with the eye level, the viewer sees neither.
The other basic principle of perspective describes an object as it moves farther and farther away from the viewer. This is best exemplified by railroad tracks. If you've ever looked down a length of railroad track, you know that the two rails are clearly separated, and yet it looks as if they meet on the horizon. When drawn in proper perspective, objects get smaller and recede to a common point, called the vanishing point.
Much of the perspective you will learn in this chapter will feel very much like geometry. You will be drawing several lines that have no purpose except to help you position objects in your drawing correctly. However, you can indicate perspective in your illustrations without ever grabbing a ruler. The following rules of perspective are very useful for simple scenes:
When two objects overlap, the one in front is closer.
Shading an object will make it recede farther than a nonshaded object.
Drawing an object smaller and with fewer details will make it seem to be farther away. A larger, more detailed object will seem closer.
As objects move away, they also move up (vertically) on the page. As objects get closer, they are drawn farther down on the page.
Simple perspective is achieved mainly through composition and the execution of line work. Sometimes the principle of altering shading is applied to the lines — with the same effect. For simple drawings, artistic perspective is sufficient.
Four examples of artistic perspective