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.

CHAPTER II

REPRESENTATION OF THE POINT, LINE, AND PLANE
13. Projection of the Point upon H and V in their Primary Position.
In Fig. 1 let H and V represent the horizontal and vertical planes
of projection in their primary position, and let 2L represent a point
in the first quadrant.
Then, according to Section 5, the horizontal. M
projection of If, or the ----
projection of Mi upon H, l^ -----
is m,,; and the vertical y/]S I
projection of JM, or the -/-/. i
projection of M upon V,
is n". The line lrI-m,, is
perpendicular to Hf and
is called the horizontal
projecting line of M.
The line M-m" is perpen- FIG. 1
dicular to V and is called the vertical projecting line of M.
N is a point in the second quadrant. Its horizontal projection
is n,, and its vertical projection is n". The line N-n,, is perpendicular to H and is called the horizontal projecting line of N. The
line N-n" is perpendicular to V and is called the vertical projecting line of N.
O is a point in the third quadrant. Its horizontal projection is
o,,, and its vertical projection is o". The line O-o,, is perpendicular to H and is called the horizontal projecting line of O. The
line O-o" is perpendicular to V and is called the vertical projecting
line of O.
P is a point in the fourth quadrant. Its horizontal projection is
p,, and its vertical projection is p". The line P-p,, is perpendicular to H and is called the horizontal projecting line of P. The
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