"Perspective is the rein and rudder of painting" - Leonardo da Vinci

Perspective views creation is an ancient art. The cave paintings representing nature, animals, and man-made objects are clear examples of artistic depiction of real-life objects as visible to the human eye. Master painters of great civilizations are among the first to popularize the concept of perspective through their wonderful building sketches and paintings.

The Plan, Elevation, Section, Parallel and Isometric views are technical requirements of engineers and architects. The detailing and other expanded views are concerned with the technical requirements of construction supervisors, workers, and users. To a great extent, these views are helping people to visualize the actual objects' functionality, size and look, but they do not represent the actual view as seen by the human eye. For public buildings and corporate houses, the "look"—aesthetic beauty—of a building is as important as its functional planning. The shape, color, shade, light, and landscaping of present day buildings are better represented in perspective views. The perspective view is the actual view as seen by the observer from a particular point. In this respect only, we refer to such views as street view, bird's eye view, grand entrance view, and so on.

The cardboard models of buildings are reduced-scaled depiction of actual buildings. It has great value in terms of understanding the actual project, but still cannot provide you with the real view as seen by observation. The photographs of cardboard models taken at appropriate angles are used as an alternative to perspective views. I don't know about you, but in this digital world I don’t want to use cardboard, paint, camera, and a film roll.

No problem! AutoCAD® can make a 3D model, render it with material, and use a camera to take a walkthrough movie. All virtual; no jungle cutting.

Perspective drawing
Perspective drawing is a drawing technique that allows the artist to show objects in three dimensions. Compared to oblique and isometric sketches, pespective drawings more closely resemble the way we see things in the real world. The most famous example of perspective viewing is a case where two railway tracks appear to meet each other at some distant point. Two railway tracks are laid at a constant distance apart, though when you view it by standing between them they appear to meet at some vanishing point.

The buildings—cubicles—are represented by three sets of parallel lines. Each set of lines runs parallel to each other infinitely. In this case, called "parallel view," the actual shape and size of objects are maintained; there is no distortion in any dimension. The structural details or sketches, containing lots of explanation and detailing, are better represented on parallel view. The oblique drawing and isometric drawing are nearer to parallel views. Isometric drawings are obtained by keeping one axis vertical and two axes are drawn at 30 degrees horizontal. Some level of distortion is observed in the case of isometric drawing, if the object is circular.

Figure 1: Parallel View

The parallel view shown in Figure 1 represents the shape and dimensions of the building.

Set-1 The lines in this set would run in one direction, parallel to each other.
Set-2 The lines in this set are perpendicular to set-1 lines and are parallel to each other.
Set-3 The lines in this set are along the height of building and parallel to each other.

The perspective views are similar to what we observe through our eyes or a camera. Perspective views are a visual pleasure and help you to appreciate the beauty of building and surroundings. The shape and dimensions of buildings represented through perspective are distorted. Depending on the vanishing point, the number of vanishing points, the horizon line, the eye (camera) level, and the point of observation, the look of the building will change dramatically. Parallel views are a technical requirement, whereas perspective views relate to the "look" of the building.

Figure 2: Perspective View

Before exploring perspective setting in AutoCAD, let's try to understand how perspectives are drawn manually. The principle behind manual drafting of perspective will help us to understand some terms related to perspective and how to obtain a similar effect in AutoCAD.

One point perspective
In one point perspective (i.e., you are standing between rails to observe them meeting at a distant point) any one set among set-1, set-2, or set-3 lines are not running parallel, but diminishing to a point called the vanishing point. The "one point" in the one point perspective is pointing towards a single vanishing point. If you maintain same vanishing point, but change the eye level, the horizon line will show you a different look of the object.

Figure 3: One point perspective

The horizontal and vertical (two sets of lines) are still running parallel. As you can see in Figure 3, the top of object is prominent in view when the object is observed with eye level (camera level) above the object. If the eye level is below the object, the bottom part of the object will attract clear attention. To understand the manual construction of one point perspective in a better way, try to redraw this figure by shifting the vanishing point on the horizon line.

The manual construction methodology of one point perspective will be clear from Figure 4. As you can see in the figure, the picture plane is drawn touching the plan of the building and eye level. The vanishing point and station point are decided in such a way that a better view is projected. The elevation of the object is used for marking true heights of various building components. One point perspective is more useful in interior decoration sketches.

Figure 4: One point perspective construction

Two point perspective
As name suggests, set-1 lines and set-2 lines are projected towards two different vanishing points. The set-3 lines—the vertical lines—are still running parallel. This is a more common and preferred way of representing buildings in perspective.

Figure 5: Two point perspective construction

Three point perspective
As the name suggests, set-1 lines, set-2 lines, and set-3 lines are projected towards three different vanishing points. This is the preferred way of representing high-rise buildings or structures in perspective.

Figure 6: Three point perspective construction

In AutoCAD, 3DORBIT and DVIEW are in charge of perspective display. They perform other duties as well, but here we will try to explore their perspective capabilities. While using 3DORBIT, perform a right-click to display a menu showing one of the items as Projection with two options in the cascading menu: 1. Parallel and 2. Perspective. You can toggle between these two views while observing the model. In AutoCAD 2007, three siblings—3DORBIT, 3DCORBIT, and 3DFORBIT—are performing a similar job. In 3D-friendly AutoCAD 2007, a toggle of Parallel and Perspective is directly available with a right-click. If you start a new drawing using acad.dwt, the Parallel view is set by default whereas Perspective will be the default when a new drawing is started with the acad3d.dwt template.

For achieving better performance in perspective setting, I am inclined to use DVIEW for some good reasons. The option called POINTS under DVIEW allows you to select the exact target and camera point in 3D space. Translating real-life situations such as observing a first-floor balcony (Target) from a street corner (Camera) is extremely easy. Once Target and Camera points are selected, you can use the DISTANCE option to convert your view in perspective. The DISTANCE option offers calculated 3D distance between Target and Camera as default selection. Users can make a numeric entry of any distance to move the camera toward the target or away from it. This is how you increase the field of view.

However, moving away from the target has its own limitations when you are working in a limited space, such as setting perspective in a kitchen, for example. In such a condition, instead of increasing distance you can opt for the Zoom option of DVIEW. Zoom behaves like the zoom lens of a real camera, allowing you to increase the field of view by maintaining a certain distance between Target and Camera.

Okay, enough talking. Let's do it practically. The option PAn also plays an important role when you wish to fine-tune your view dynamically. The CLip option facilitates the front and back clipping of the model. Clipping is like cutting the model perpendicular to an imaginary line joining Target and Camera. I love clipping—it creates dramatized views of buildings and mechanical models.

A partially modeled British bungalow would be my model on the ramp. The Plan view of the bungalow (Figure 7) would be more suitable for setting perspective through DVIEW command. The 3D view shown in Figure 8 is purely for understanding the dimensional space available for setting Target and Camera. Points marked as A, B, C, and D are locations marked for setting Target/Camera.

Figure 7

Figure 8

In World UCS plan view, please follow the command sequence as given below.

Command: DV
DVIEW
Select objects or <use DVIEWBLOCK>: ALL
214 found
Select objects or <use DVIEWBLOCK>: Press Enter
Enter option [CAmera/TArget/Distance/POints/PAn/Zoom/TWist/CLip/Hide/Off/Undo]: PO
Specify target point <34.9919, 11.0458, 0.1704>: .XY of [select point near A] (need Z): 2
Specify camera point <34.9919, 11.0458, 1.1704>: .XY of [select point near B] (need Z): 2
Enter option
[CAmera/TArget/Distance/POints/PAn/Zoom/TWist/CLip/Hide/Off/Undo]: D
Specify new camera-target distance <40>: Press Enter
Enter option
[CAmera/TArget/Distance/POints/PAn/Zoom/TWist/CLip/Hide/Off/Undo]: Press Enter
Regenerating model.

The resulting perspective would be something similar to the figure shown below.

Figure 9

How to enter .XY of [select point near A] (need Z): 2 sequence on AutoCAD prompt.

When Specify target point appears on the AutoCAD command prompt, Write .xy and Press Space Bar; "of" will appear automatically after .xy then Select point. As computer expects Z from you (need Z) will appear after 'of'. Write Z value (In this case 2 units).

All in all, .XY allows selection of point in the XY plane and the Z value lifts that point in Z direction.

The change in Z value has a dramatic affect on perspective. In the above command sequence, keep everything the same and try it with Zero value for (need Z) in target point and 6 for (need Z) in camera point. Figure 10 shows the change observed in horizon line and appearance of perspective.

Figure 10

The perspective view created by setting target near point C and camera near point D would be something like the figure shown below. Click here to download the 3D model used in this article.

My thanks to the nice people who have used "real" cameras for taking such nice photographs of the buildings shown in this article. Real and virtual worlds can exist together!

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Submitted by Mohmed Zuber Shaikh. Mohmed is a civil engineer in Bharuch, employed by Sardar Sarovar Narmada Nigam Limited, Gandhinagar (India). He can be contacted via email at mzyshaikh1@yahoo.co.in