Orthographic Projections, Continued
Normal and
oblique lines
(Continued)
Figure 6-32 shows a pictorial drawing of a triangular object in the upper-left
corner. The right side is presumed parallel to the profile plane of projection,
the bottom view parallel to the horizontal plane, and the front view parallel to
the vertical plane. The line AB is oblique to all three planes. The true
length of AB is shown in the small triangle to the left of the single-view
projection. It is the length of the hypotenuse of a triangle with the altitude
equal to the length of AB as it appears in the top view of the multiview
projection. AB is foreshortened in all of the orthographic views.
Figure 6-32.—Oblique lines foreshortened in all orthographic
views.
Circles, arcs,
and ellipses
In multiview projections, a circle on surfaces parallel to the plane of
projection appears as a circle. A circle on a surface that is oblique to the
plane of projection appears as an ellipse.
6-38
