may also be shown on this single plane byconstructing the receding projection lines of theobject at an angle other than perpendicular to theplane of projection.Figure 5-46 shows the same object by bothorthographic and oblique projection. The blockis placed so that its front surface (the surfacetoward the plane of projection) is parallel to theplane of projection. You can see that theorthographic projection shows only this surfaceof the block. The oblique projection, on the otherhand, shows the front surface and also the topand side surfaces. The orthographic projectionshows only two dimensions: length and width. Theoblique projection shows three: length, width, andthickness. Oblique projection, then, is one methodby which an object can be shown, in a single view,in all three dimensions.There are two types of oblique single-planeprojections: CAVALIER and CABINET.Cavalier ProjectionCAVALIER PROJECTION is a form ofoblique projection in which the projection linesare presumed to make a 45-degree vertical and a45-degree horizontal angle with the plane ofprojection. Assume that in figure 5-47 the lineXX' represents a side-edge view of the plane ofprojection, and that the square ABCD representsa side of a cube, placed with its front face parallelto, and its top face perpendicular to, the planeof projection. You can see that the projectedlengths of AB and AD are the same as the actuallengths.Now assume that the line XX' in figure 5-47represents a top-edge view of the plane ofFigure 5-46.—Oblique and orthographic projections of thesame object.Figure 5-47.—Angle of projection lines in a cavalierprojection.projection, and that the square ABCD representsthe top of the cube. You can see again that theprojected lengths of AB and AD are the same asthe actual lengths of AB and AD.In a cavalier projection, then, any line parallelto or perpendicular to the plane of projection isprojected in its true length. Figure 5-48 shows acavalier projection of the cube shown in figure5-47. You start by drawing the axis, whichconsists of the front axes OA and OB and thereceding axis OC. The front axes are alwaysperpendicular to each other; the receding axisFigure 5-48.—Cavalier projection of a cube.5-25
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