Basic Principles Of Perspective Drawing For The Technical Illustrator

Perspective Basics

A thorough understanding of the principles of perspective is essential to creating an accurate and visually appealing piece of art. The impression that the perspective techniques in the preceding tutorial make on a viewer are so strong that once mastered, the illusion of 3 dimensional depth remains even though the visual trickery involved in the process has been revealed. Additionally, a lay person with no technical understanding of the principles of perspective has an intuitive negative reaction to a piece of art if something is amiss.

Any good technical illustration starts with well executed line art. If you are working from any type of reference other than a CAD output in the desired angle, you will need to have a strong fundamental understanding of the principles of perspective drawing. This page will cover the various types of perspective angles you will encounter. In the tutorial lessons that follow this page, you will be given the tools needed to map out a perspective grid in any situation. From this grid, you will be able to create realistic three dimensional drawings from flat or "Off Angle" reference.

The three photos below demonstrate the difference between 1-Point, 2-Point, and 3-Point Perspective. The first photograph (Fig. 1) is an example of one-point perspective. All of the major Vanishing Points for the buildings in the foreground of Fig. 1 converge at one central location on the horizon line. The angle of view or Point Of View (POV) in Fig. 1 is referred to as Normal View perspective. In Fig. 2 the vanishing points for the two opposing faces of the center foreground building project towards two different vanishing points on the horizon line. In Fig. 3 we see that the horizontal building elements project to the left and right horizon and the vertical building elements project to a central vanishing point in the sky. This upper vanishing point is called the Zenith. If one were looking down on the object from a Bird's Eye perspective, the vanishing point below the horizon and would be called the Nadir.

Deconstructing "Perspective" from Photography

In the next three diagrams, you will see the same three photographs with Vanishing Point trajectory lines (magenta) and Horizon Lines (blue) traced over the subject matter. Fig. 4 and Fig. 5 are both examples of Normal View perspective. A Normal View angle places the Horizon Line at a natural height as if the viewer was looking straight forward without tilting the head/camera up or down. In these two examples, you will notice that all of the vertical features of the buildings are straight up and down.

Fig. 6 is an example of a Worm's Eye perspective. In Fig. 6 the head/camera is tilted upward placing the Horizon below the picture. The perspective when the view is tilted in an upward direction, creates a third vanishing point at the Zenith. All of the vertical building features will converge at this upper vanishing point. If we were looking down on a subject, the viewing angle would be a Bird's Eye View and the vertical details would converge at the Nadir.

This technique of tracing parallel lines to their convergence point would be used to construct a Perspective Grid from exiting photographic material. Each convergence point will represent the exact location of the Horizon, Zenith, or Nadir in that photograph.

The Illusion of Depth

In the preceding photographic examples you will notice that as an object recedes towards a Vanishing Point (infinity) it appears to get smaller. This phenomenon is due to the fact that the "viewer" is at a steeper angle of view when looking an object that is in close proximity as opposed to an object of the same size that is farther away and therefor, viewed at a shallower angle. The "Picture Plane" shown in the example below represents the point where the observer perceives perspective.

In the physical world, the "picture plane" (as shown below) represents the point at which the observer perceives perspective as interpreted by the lens of the eye. In the world of illustration, the "picture plane" is actually the flat surface of the paper or computer screen, and the perception of 3 dimensional depth or perspective is an artificial illusion.

Drawing in Perspective

The following diagram Fig. 7 is a sample of the typical reference material you might expect to receive on a technical illustration project. All of the major plan and elevation views are represented here as well as an Isometric view. From this reference, we will construct a variety of perspective views in the tutorials that follow this page.

In the following six examples, you will see a perspective grid and our subject in various aspects discussed in the previous paragraph. Fig. 8 is a Normal View 1 Point Perspective drawing. Fig. 9 is a Worm's Eye View 1 Point Perspective drawing. Fig. 10 is a Bird's Eye 1 Point Perspective drawing. Fig. 11 is a Bird's Eye or High 3/4 View 2 Point Perspective drawing. Fig. 12 is a Bird's Eye 3 Point Perspective drawing. If you were to extend the vertical vanishing point lines downward, they would converge at the Nadir Station point.

Perspective vs Isometric Drawing

By now you may have noticed that perspective drawing techniques differ from other types of commonly seen technical imagry. In Fig. 13 you have three examples of 3/4 view illustrations that are not in perspective view. They are classified as Isometric, Dimetric, and Trimetric drawings. In these types of illustrations all parallel lines remain parallel and therefor, never converge at a single point. Although they can be very useful for conveying technical information, they lack the quality of realism when compared to the perspective view drawing example in Fig. 14.