- Understanding Solid Objects
- Understanding Sketching Techniques
- 3.1 Technique of Lines
- 3.2 Sketching Straight Lines
- 3.3 Sketching Circles, Arcs, and Ellipses
- 3.4 Maintaining Proportions
- 3.5 One-View Drawings
- 3.6 Pictorial Sketching
- 3.7 Projection Methods
- 3.8 Axonometric Projection
- 3.9 Isometric Projection
- 3.10 Isometric Drawings
- 3.11 Making an Isometric Drawing
- 3.12 Offset Location Measurements
- 3.13 Hidden Lines and Centerlines
- 3.14 Angles in Isometric
- 3.15 Irregular Objects
- 3.16 Curves in Isometric
- 3.17 True Ellipses in Isometric
- 3.18 Orienting Ellipses in Isometric Drawings
- 3.19 Drawing Isometric Cylinders
- 3.20 Screw Threads in Isometric
- 3.21 Arcs in Isometric
- 3.22 spheres in Isometric
- 3.23 Oblique Sketches
- 3.24 Length of Receding Lines
- 3.25 Choice of Position in Oblique Drawings
- 3.26 Ellipses for Oblique Drawings
- 3.27 Angles in Oblique Projection
- 3.28 Sketching Assemblies
- 3.29 Sketching Perspectives
- 3.30 Curves and Circles in Perspective
- 3.31 Shading
- 3.32 Computer Graphics
- 3.33 Drawing on Drawing
- Key Words
- Chapter Summary
- Worksheets
- Review Questions
- Sketching Exercises
This chapter is from the book
This chapter is from the book
This chapter is from the book
3.29 Sketching Perspectives
Perspective pictorials most closely approximate the view produced by the human eye. Perspective views are the type of drawing most like a photograph. Examples of a perspective drawing can be seen in Figures 3.69, 3.70a, and 3.72. Although complex perspective views are time consuming to sketch, they are easy to create from 3D CAD models.
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3.69 Perspective Drawing Theory
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3.70 Perspective vs. Oblique. Perspective drawings appear more natural than oblique drawings.
Unlike parallel types of projection, perspective projectors converge. The point at which the projectors converge is called the vanishing point. This is clearly seen in Figure 3.70a.
The first rule of perspective is that all parallel lines that are not parallel to the picture plane vanish at a single vanishing point, and if these lines are parallel to the ground, the vanishing point will be on the horizon. Parallel lines that are also parallel to the picture plane remain parallel and do not converge toward a vanishing point (Figures 3.71 and 3.72).
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3.71 Looking through the Picture Plane
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3.72 A Perspective
When the vanishing point is placed above the view of the object in the picture plane, the result is a bird’s-eye view, looking down onto the object. When the vanishing point is placed below the view of the object, the result is a worm’s-eye view looking up at the object from below (see Figure 3.74 on page 107).
There are three types of perspective: one-point, two-point, and three-point perspective, depending on the number of vanishing points used.
The Three Types of Perspective
Perspective drawings are classified according to the number of vanishing points required, which in turn depends on the position of the object with respect to the picture plane.
If the object sits with one face parallel to the plane of projection, only one vanishing point is required. The result is a one-point perspective, or parallel perspective.
If the object sits at an angle with the picture plane but with vertical edges parallel to the picture plane, two vanishing points are required, and the result is a two-point perspective, or an angular perspective. This is the most common type of perspective drawing.
If the object sits so that no system of parallel edges is parallel to the picture plane, three vanishing points are necessary, and the result is a three-point perspective.
One-Point Perspective
To sketch a one-point perspective view, orient the object so that a principal face is parallel to the picture plane. If desired, this face can be placed in the picture plane. The other principal face is perpendicular to the picture plane, and its lines will converge toward a single vanishing point.
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8:12 Train as Seen by 8:12 1/2 Commuter (Excerpted from Droodles – The Classic Collection by Roger Price ©2000 by Tallfellow Press. Used by permission. All rights reserved.)
STEP by STEP: ONE-POINT PERSPECTIVE
To sketch the bearing in one-point perspective—that is, with one vanishing point—follow the steps illustrated below.
Sketch the true front face of the object, just as in oblique sketching. Select the vanishing point for the receding lines. In many cases it is desirable to place the vanishing point above and to the right of the picture, as shown, although it can be placed anywhere in the sketch. However, if the vanishing point is placed too close to the center, the lines will converge too sharply and the picture will be distorted.
Sketch the receding lines toward the vanishing point.
Estimate the depth to look good and sketch in the back portion of the object. Note that the back circle and arc will be slightly smaller than the front circle and arc.
Darken all final lines. Note the similarity between the perspective sketch and the oblique sketch earlier in the chapter.
Two-Point Perspective
Two-point perspective is more true to life than one-point perspective. To sketch a two-point perspective, orient the object so that principal edges are vertical and therefore have no vanishing point; edges in the other two directions have vanishing points. Two-point perspective is especially good for representing buildings and large civil structures, such as dams or bridges.
STEP by STEP: TWO-POINT PERSPECTIVE
To sketch a desk using two vanishing points, follow these steps.
Sketch the front corner of the desk at true height. Locate two vanishing points (VPL and VPR) on a horizon line (at eye level). Distance CA may vary—the greater it is, the higher the eye level will be and the more we will be looking down on top of the object. A rule of thumb is to make C–VPL one third to one fourth of C–VPR.
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Estimate depth and width, and sketch the enclosing box.
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Block in all details. Note that all parallel lines converge toward the same vanishing point.
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Darken all final lines. Make the outlines thicker and the inside lines thinner, especially where they are close together.
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Three-Point Perspective
In three-point perspective, the object is placed so that none of its principal edges is parallel to the picture plane. Each of the three sets of parallel edges has a separate vanishing point. See Figure 3.73.
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3.73 Three-Point Perspective
Bird’s-Eye View versus Worm’s-Eye View
The appearance of a perspective sketch depends on your view-point in relation to the object. Select some reachable object in the room and move so that you are looking at it from above and really notice its shape. Now gradually move so that you are looking at it from below. Notice how the change of viewpoint changes the appearance of its surfaces—which ones are visible and their relative size.
The horizon line in a perspective sketch is a horizontal line that represents the eye level of the observer. Locating the sketched object below the horizon line produces a view from above (or a bird’s-eye view). Locating the sketched object above the horizon line produces a view from below (or a worm’s-eye view). Figure 3.74 illustrates the horizon line in a drawing and the effect of placing the object above or below the horizon line.
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3.74 (a) Object below the Horizon Line; (b) Object above the Horizon Line