Descriptive geometry . Fig. 179. Fig. 180. (Prob. 13, § 119); in the figure, this is done by using the aux-iliary plane X, perpendicular to II. Then ahbh and avbv are theprojections of the required shortest distance, the true lengthof which may be found by Problem 3 (§ 78 or § 80). Special Case i Fig. 180). The given plane Q is parallel tothe ground line. The required perpendicular from a is evi-dently a profile line, and may be drawn directly in the profileprojection as soon as the profile views of the given point andand plane are obtained. In (ids case it is not necessary tohave the H- and ^
Descriptive geometry . Fig. 179. Fig. 180. (Prob. 13, § 119); in the figure, this is done by using the aux-iliary plane X, perpendicular to II. Then ahbh and avbv are theprojections of the required shortest distance, the true lengthof which may be found by Problem 3 (§ 78 or § 80). Special Case i Fig. 180). The given plane Q is parallel tothe ground line. The required perpendicular from a is evi-dently a profile line, and may be drawn directly in the profileprojection as soon as the profile views of the given point andand plane are obtained. In (ids case it is not necessary tohave the H- and ^projections of the perpendicular in order toknow its actual length ; these projections are, however, usuallyconsidered a part of the problem, and are obtained bj project-ing from the profile view. 106 DESCRIPTIVE GEOMETRY [XII, § 121 121. The Projection of a Point or Line on a Plane. The projection of a point on a plane is the foot of the perpendiculardropped from the point to the plane. This definition is notconfi
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