Elements of descriptive geometry, with applications to isometric projection and othe forms of one-plane projection; a text-book for colleges and ingineering schools by O. E. Randall.

THE POINT, LINE, AND PLANE

7

The point p" will remain stationary, while the point p,, will
move in the arc of a circle with e as a center, and fall at p, in the
line e-p'".
It will be noticed that in the revolution vertical projections
remain stationary, while horizontal projections move in arcs of
circles with centers in
G-JL, and fall upon V in
straight lines drawn.-., m
through the correspond-
ing vertical projections
perpendicular to G-L. ' n b
After the revolution of /.
the plane H, or when the -- i-
planes are in their posi- p
tion of coincidence, the
projections will appear as
shown in Fig. 3, where
that portion of the plane
of the paper above G-L,
regarding the plane of the paper as vertical, represents both that
portion of V above H and that portion of H back of V, and where
that portion of the plane of the paper below G-L represents both
To, that portion of V below
1n, rn H and that portion of H
Vabove H in front of V.
H behind V Again, referring to
-— G - - - -- ---- L Fig. 2, if the plane V be
IVbo:revolved about G-L as an
"o' ' V below H
{P, 'Hnfrontof Vaxis until that portion of!, H in front of V
[ ~ Hnp fotf V above falls upon that
^Im ~ portion of H back of V, and
FIG. 3 that portion of V below H
falls upon that portion of
H in front of V, the horizontal projections will remain stationary,
while the vertical projections will move in arcs of circles with
centers in G-L, and fall upon H in straight lines drawn through
the corresponding horizontal projections perpendicular to G-L.