If transparent plane is placed horizontally above the object,
the projection on this plane found by extending perpendiculars
to it from the object, will give the appearance of the object as
if viewed from directly above and will show the distance from
frontal plane. Then the horizontal plane is now rotated into
coincidence with the frontal plane. Now again a third plane,
perpendicular to the first two called profile plane are used to
view an object from the side.
C. The Six Principal Views
Let us surround the object entirely by asset of six planes,
each at fight angles to each other. On these planes, views of
the object can be obtained as is seen from the top, front, and
right side, left side, bottom and rear.
Think now of the six sides, or the plane of the paper. The front
is already in the plane of the paper, and the other sides are,
as it were, hinged and rotated in position as shown. The
projection on the frontal plane is the front view vertical
projection, or front elevation, that on the horizontal plane, the
top view, horizontal projection, or plan, that on the side, profile
view, side view, profile projection, or side elevation. By
reversing the direction of sight, a bottom view is obtained
instead of a top view, or a rear view instead of a front view.