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3.24 Length of Receding Lines

Theoretically, oblique projectors can be at any angle to the plane of projection other than perpendicular or parallel. The difference in the angle you choose causes receding lines of oblique drawings to vary in angle and in length from near zero to near infinity. However, many of those choices would not produce very useful drawings. Figure 3.58 shows a variety of oblique drawings with different lengths for the receding lines.


3.58 Foreshortening of Receding Lines

Because we see objects in perspective (where receding parallel lines appear to converge) oblique projections look unnatural to us. The longer the object in the receding direction, the more unnatural the object appears. For example, the object shown in Figure 3.58a is an isometric drawing of a cube in which the receding lines are shown full length. They appear to be too long and they appear to widen toward the rear of the block. Figure 3.59b shows how unnatural the familiar pictorial image of railroad tracks leading off into the distance would look if drawn in an oblique projection. To give a more natural appearance, show long objects with the long axis parallel to the view, as shown in Figure 3.60.


3.59 Unnatural Appearance of Oblique Drawing


3.60 Long Axis Parallel to Plane of Projection

Cavalier Projection

When the receding lines are true length—(the projectors make an angle of 45° with the plane of projection)—the oblique drawing is called a cavalier projection (Figure 3.58a). Cavalier projections originated in the drawing of medieval fortifications and were made on horizontal planes of projection. On these fortifications the central portion was higher than the rest, so it was called cavalier because of its dominating and commanding position.

Cabinet Projection

When the receding lines are drawn to half size (Figure 3.58d), the drawing is known as a cabinet projection. This term is attributed to the early use of this type of oblique drawing in the furniture industries. Figure 3.61 shows a file drawer drawn in cavalier and cabinet projections.


3.61 Comparison of (a) Cavalier and (b) Cabinet Projections

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