Figure 5-54.-Transferring an angle in oblique projection.Figure 5-55.-Cavalier projection of a circle on a recedingsurface.size; an angle on any other surface will not. Theupperpart of figure 5-54 shows a two-view multi-view projection of a block. It has a 30-degreeangle on the top face and another on the frontface. In the cavalier projection below, the angleon the front face still measures 30 degrees; thaton the top face measures only about 9 degrees.You transfer the top face angle by locating theend points of the line by measurements alongregular lines.CIRCLES IN OBLIQUE.— In an obliqueprojection, a circle on the surface parallel to theplane of projection will appear as a circle. Acircle on any other surface will appear as anellipse, as shown in figure 5-55. The upperpartof this figure shows a two-view multi-viewprojection of a block with a circle on its upperface. The lower part of this figure shows a cavalierprojection in which the circle appears as an ellipse.Each of the conjugate (joined together) diametersof the ellipse is equal to the diameter of the circle.PERSPECTIVE PROJECTIONAND PERSPECTIVE DRAWINGPERSPECTIVE PROJECTION (fig. 5-2) isobtained when the projection lines converge to apoint that is at a finite distance from the planeof projection. Each projection line forms adifferent angle with the plane of projection,giving the viewer a three-dimensional picture ofthe object. This type of projection, however,cannot accurately convey the structural featuresof a building; hence, it is not adequate forworking drawings.On the other hand, of all the three-dimensional single-plane drawings, PERSPEC-TIVE DRAWINGS are the ones that lookthe most natural. At the same time, theyare also the ones that contain the most errors.Lines that have the same length on the objecthave different lengths on the drawing. Nosingle line or angle on the drawing has alength or size that has any known relationshipto its true length or size when projected throughperspective projections.Perspective drawing is used only in drawingsof an illustrative nature, in which an objectis deliberately made to appear the way it looksto the human eye. Most of the drawings you willprepare will be drawings in which accuracy,rather than eye appearance, will be the chiefconsideration. Consequently, you will not beconcerned much with perspective drawing.If you are required to prepare perspectivedrawings, refer to Illustrator Draftsman,NAVEDTRA 10472, or civilian publications, suchas Architectural Drawing and Light Constructionand Architectural Graphic Standards.5-28
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