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Sketching

Chapter Description

In this sample chapter from Engineering Graphics with AutoCAD 2020, author Bethune presents the fundamentals of freehand sketching as applied to technical situations. It includes both two-dimensional and three-dimensional sketching. Like any skill, freehand sketching is best learned by lots of practice.

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Engineering Graphics with AutoCAD 2020

Engineering Graphics with AutoCAD 2020

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4-12 Perspective Sketches

Perspective sketches are sketches whose receding lines converge to a vanishing point. Perspective sketches are visually accurate in that they look like what we see: Objects farther away appear smaller than those that are closer.

Figure 4-25 shows a comparison among the axis systems used for oblique, isometric, and two-point perspective drawings. The receding lines of the perspective drawings converge to vanishing points that are located on a theoretical horizon. The horizon line is always located at eye level. Objects above the horizon line appear to be above you, and objects below the horizon appear to be below you.

Perspective drawings are often referred to as pictorial drawings. Figure 4-26 shows an object drawn twice: once as an isometric drawing and again as a pictorial, or two-point, perspective. Note how much more lifelike the pictorial drawing looks in comparison with the isometric drawing.

Figure 4-27 shows a perspective sketch based on only one vanishing point. One-point perspective sketches are similar to oblique sketches. The front surface plane is sketched by using a 90° axis, and then receding lines are sketched from the front plane to a vanishing point. As you practice sketching, eventually you will not need to include a vanishing point, but will imply its location.

Figure 4-28 shows how to sketch circular shapes in one- and two-point perspective sketches. In each style, the axis lines consist of a vertical line and a line that is aligned with the receding edge lines. Circular shapes in perspective drawings are not elliptical, but are irregular splines. Each surface will require a slightly different shape, depending on the angle of the receding lines, to produce a visually accurate circular shape.

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