7.3. Projection of Point
Since a point is a location in space and not a dimensional
form, it must be located by measurements taken from
established reference line. The two figures below show the
glass box method of orthographic projection illustrated
pictorially and orthographically. These two figures represent
the projection of point 1 in the three principal planes, frontal
(1F), horizontal (1H), and profile (1P). In glass box method, it
is assumed that each mutually perpendicular plane is hinged
so as to be revolved in to the planes of the paper. “The
intersection line of two successive (perpendicular) image
planes is called fold line/ reference line.” All measurements
are taken from fold lines to locate a point is space. A fold
line/reference line can be visualized as the edge view of a
reference plane.
A point can be located by means of verbal description by
giving dimensions from fold/ reference lines. Point 1 is below
the horizontal plane (D1), to the left of the profile plane (D2),
and behind the frontal plane (D3). D1 establishes the
elevation or height of the point in front and side view, D2 the
right, left location or width in the front and top view, and D3
the distance behind the frontal plane (depth) in the top and
side view.