Orthographic Projections, ContinuedNormal andoblique linesA normal line in a multiview projection is parallel to two of the planes of‘projection and perpendicular to the third. A line parallel to a plane ofprojection appears in true length depending on the scale of the drawing. Aline perpendicular to a plane of projection appears on that plane as a point.A line perpendicular to one plane of projection must be parallel to the othertwo, but a line parallel to one plane of projection may be oblique to one orboth of the others. This type of oblique line appears in true length in a viewon the plane of projection to which it is parallel but appears foreshortened inall regular views of the object.Figure 6-31 is a pictorial drawing of a block in the upper-left corner. Placingthe front face parallel to the vertical plane in a multiview projection placesthe bottom face parallel to the horizontal plane and right-side face parallel tothe profile plane. Line AB is parallel to the vertical plane but oblique to boththe horizontal and the profile planes. Only in the front and back views is lineAB shown in true length. In all other views AB is foreshortened.Figure 6-31.—Line AB in true length on the front and backview.Continued on next page6-37
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