Descriptive geometry . Fig. 127. t, in VQ, and find th on GL. Then, by § 99, Ah passes throughth and is parallel to HQ, while Av passes through f and isparallel to GL. Similarly, a vertical principal line, B, may be drawn by firstassuming its ZZ-trace, s, on HQ. 101. To Project the Principal Lines of a Plane Parallel tothe Ground Line. To draw a principal line of a plane whenthe plane is parallel to the ground line, as Q, Fig. 128, find the ; VQ \fl uv Av / 1 / 1 [ \\ Uh Ah HQ D. X Fig. profile trace, PQ, of the given plane. On PQ assume anypoint, up, as the profile trace of the req
Descriptive geometry . Fig. 127. t, in VQ, and find th on GL. Then, by § 99, Ah passes throughth and is parallel to HQ, while Av passes through f and isparallel to GL. Similarly, a vertical principal line, B, may be drawn by firstassuming its ZZ-trace, s, on HQ. 101. To Project the Principal Lines of a Plane Parallel tothe Ground Line. To draw a principal line of a plane whenthe plane is parallel to the ground line, as Q, Fig. 128, find the ; VQ \fl uv Av / 1 / 1 [ \\ Uh Ah HQ D. X Fig. profile trace, PQ, of the given plane. On PQ assume anypoint, up, as the profile trace of the required principal projections of this line are parallel to the ground line. X, § 103] PARALLEL LINES AND PLANES 77 102. A Plane Containing a Line Parallel to H or V. Anyplane, as Q or R, Fig. 129, which is passed through an H-parallel will have its //-trace parallel to the //-projection ofthe line. (Converse of § 100.) Similarly, any plane passed through a F-parallel will haveits F-trace parallel to the F-projection of the line. Any plane, as Q, Fig. 128, which contains a line parallel toboth H arid V will have both its H- and F-traces parallel tothe ground line. (Converse of § 101.) 103. Parallel Planes. If two planes are parallel, their corre-sponding traces are parallel. Let Q and R be the given planes. Let Q intersect H inHQ, and R intersect // in HR. The figure is left for thestudent to draw. Now when two parallel planes, Q and R,are intersected by a third plane, H, the lin
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