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.

26

DESCRIPTIVE GEOMETRY

of the vertical line and above the horizontal line; points in the
third quadrant have their profile projections to the right of the
vertical line and below the horizontal line; points in the fourth
quadrant have their profile projections to the left of the vertical line and below the horizontal line.
Distances of points in front or back of V are indicated by the
distances of their profile projections to the left or right of the
vertical line. Distances of points above or below H are indicated
by the distances of their profile projections above or below the
horizontal line.
54. Representation of the Straight Line upon a Profile Plane of
Projection. The profile projection of a straight line is determined
by the profile projections of two points of the line.
- -- - - - - -. -----. ---—.............. _-' —......
N _\ \\__ 1___ I p' -_
FIG. 36
In Fig. 36, which is a pictorial drawing, let i-N represent the
given line and let the plane P represent the profile plane of
projection.
The profile projection of M is HMP, and the profile projection of
N is NP. The line MP-NAP is the profile projection of M-N.
Now if we revolve the profile plane of projection about its vertical trace P-p' until it coincides with V, MP will fall at mp, and
NP will fall at npV. The line nipV-np' is the profile projection of
M-NT after the revolution.