Creating the Illusion of Depth with Linear Perspective
Introduction
Linear perspective is a technique for using lines to create the illusion of depth. Perspective is always created from the point of view created by you, the artist. The viewer of the painting then shares the same point of view.
Historical Background
Filippo Brunelleschi (Brunellessski) 13871446 is credited with discovering linear perspective. (If knowledge of perspective was known to the Greeks and Romans, it was definitely lost during the middle ages. For a thousand years prior to the Renaissance, paintings were flat, without any sense of depth.)
Around 1420, Brunelleschi observed that with a fixed single point of view, parallel lines appear to converge at a single point in the distance. Brunelleschi applied a single vanishing point to a canvas and discovered a method for calculating depth.
In a famous experiment, Brunelleschi used mirrors to sketch the Florence baptistry in perfect perspective. He was able to mathematically calculate the scale of objects within a painting in order to make them appear realistic. It was a monumental discovery and a remarkable demonstration of the principles, but it was not until another artist, Leon Battista Alberti wrote down the rules of linear perspective that artists were able to learn this new system and apply it to their paintings.
OnePoint Linear Perspective
in onepoint perspective, you are looking at the front of a building....in 2point perspective you are looking at a corner of the building.
the front of the building ... horizontal and vertical lines parallel to sides and top and bottom of building.
the sides, top and bottom all recede away from you ... the parallel lines that recede converge at the VP on the eye level line...all windows and doors on a receding wall will ...
Onepoint perspective uses four types of lines and one point to create the illusion of 3D space on a 2D surface. The four types of lines are the eye level line, converging lines, horizontal lines, and vertical lines. The point that is always somewhere on the eye level line is the vanishing point.
Eye Level: Eye level is the height of the viewer's eyes above the ground. When a person is sitting on the ground, the eye level is lower than when a person is standing. The eye level is higher if the person is standing on a table.
If you raise your eyes to see something, it is above eye level. If you lower your eyes to see something, it is below eye level.
To visualize how the eye level line is projected onto the scene you are painting, imagine yourself sitting in a room sketching the interior. Now imagine that as you sit there, the room is filled with water until it reaches the level of your eyes. Everything that is under water is below eye level. Everything that is above the water is above eye level. The "high water mark" around the walls and on every object that rises out of the water is the eye level line. No matter in what direction you look this highwater mark appears to your eye as a straight, horizontal line across the objects of the room.
You can find the eye level line in a scene by holding your pencil horizontally and at arm's length. Close one eye. Hold the brush level with your eyes. Notice where your brush intersects objects on the wall. Now visualize an imaginary line drawn horizontally through this point on the wall.
We represent this highwater mark or eye level with a straight, horizontal line across the paper. Objects drawn above this line are above eye level. Objects drawn below this line are below eye level.
The you determine where the eye level line is placed. Your eye level and that of the viewer will be the same. You control how the scene will be experienced by the viewer.
If your objective is to create a realistic painting, eye level must remain consistent for all objects in the composition. If objects are painted from different eye levels, the painting will be confusing. Objects will look as if they belong in different paintings. This confusion is often introduced into a painting when several reference photos are combined.
There is only one specific case where the eye level line is the same as the horizon, or the line where the sky meets the ground or the sea. This occurs when you are overlooking the ocean or a vast expanse of level ground. In all other situations, it is confusing to refer to the eye level line as the horizon line.
In addition to the eye level line, there are three sets of parallel lines that are important to creating the illusion of depth with linear perspective: vertical, horizontal, and converging.
Vertical Lines: In onepoint perspective, vertical lines (telephone poles, trees, corners of buildings, sides of doors and windows) are all parallel to each other and to the sides of the paper. (NOTE: These vertical lines are often distorted in photographs). Parallel vertical lines do not recede; they do not converge at the Vanishing Point. They remain vertical and parallel.
Horizontal Lines: In onepoint perspective, there are two kinds of horizontal lines: those that converge at the vanishing point and those that do not. If you are looking directly at the side of a building, the top and the bottom of the building will be horizontal, parallel lines. These lines will both be parallel to the top and the bottom of the paper. However, the horizontal lines that are on the side of the building that is receding away from you will appear to converge at the vanishing point on the eye level line.
Converging Lines (orthogonal lines): All linear perspective is based on the idea that parallel lines receding from you seem to meet in the distance. This is an optical illusion, because the lines are actually parallel and never meet. You know the railroad tracks are parallel, yet they appear to meet at a point in the distance.
All converging lines meet at a vanishing point that is always on the eye level line. Converging lines above the eye level line will come down to the vanishing point. Converging lines below the eye level line will come up to the vanishing point. If an object is partly above and partly below the eye level line, the converging lines will come up and go down.
You can find both the vanishing point and the eye level line in a photograph by extending the receding parallel lines until they cross. The point where they cross is the vanishing point. A parallel line drawn through that point is the eye level line.
Vanishing Point: The point where receding parallel lines converge is called a vanishing point. In onepoint perspective, all receding lines meet at this single vanishing point. The vanishing point is always on the eye level line.
The vanishing point can be anywhere on the eye level line. If the viewer is standing to the left, the vanishing point will be to the left. If the viewer is standing to the right, the vanishing point will be to the right.
SECRET: You will never have to use perspective lines, eye level lines, and vanishing points if you get the angles right in the first place. There are several tools that will help you determine the angles in a photograph or in a scene.
 Pencil: Hold a pencil at arm's length with one eye closed. Place the pencil on the angle and notice its position relative to a clock. Is it at 1 o'clock, 4:30 or 9? Reproduce the same angle on your paper.
 Rolling Ruler: Place your paper next to the photograph. Make sure the edges of the paper are parallel to the edges of the photograph. Place the rolling ruler on the angle line. Roll the ruler to your paper, retaining the same angle. Draw the angle.
 Parallel Rulers: Position the parallel rulers on the angle. Walk the rulers to the correct position on your paper and draw the angle.
 "Perspective Jaws": Position one of the jaws so that it is parallel to the side of the photograph or parallel to a vertical object in the scene. Open the other jaw until it corresponds to the angle you are measuring. Carefully move the open jaws to your paper, align the vertical jaw to the side of the paper, position the jaws where you want to draw the angle.
You can make your own perspective jaws with two strips of cardboard or plastic joined at one end with a brad or with a bolt and one or two nuts. It works best with one normal nut and one locking nut. The nuts need to be tight enough that the jaws will not slip as you moved from one place to another.
Special Cases in OnePoint Perspective
