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.

SUPPLEMENTARY PLANES OF PROJECTION

25

It will also be observed that when the projections of a point
upon H, V, and P are given, the position of the point with reference
to these three planes of projection is definitely determined.
Revolve the plane P about its vertical trace as an axis until
that portion of the plane P in front of V falls on V to the left of
the axis, and that portion of P back of V falls on V to the right
of the axis.
Each profile projection will move in a plane parallel to H, and
in the arc of a circle with center in the axis. MP will fall upon V
at a point as far to the left
of the axis as ll was originally in front of V, and as far mrp
above G-L as M was origi-:
nally above H. ' i
NP will fall upon V at a G. P, L
point as far to the right of:
the axis as N was originally.. bpr
behind V, and as far above ppt —I
G-L as N was originally
above H. OP will fall upon
V at a point as far to the
right of the axis as 0 was FIG. 35
originally behind V, and as far below G-L as O was originally
below H. PP will fall upon V at a point as far to the left of the
axis as the point P was originally in front of V, and as far below
G-L as the point P was originally below I.
After the profile plane has been thus revolved, the profile projections of M, N, 0, and P will appear as shown in Fig. 35.
This is the picture of the four points which the observer
would have if he stood at an infinite distance to the right and
looked along visual lines parallel to G-L. H would appear as
a horizontal line corresponding with G-L in Fig. 35, and the
vertical plane would appear as a vertical line corresponding with
p,-P-P'.
Here points in the first quadrant have their profile projections
to the left of the vertical line and above the horizontal line; points
in the second quadrant have their profile projections to the right