In figure above, each end points of line 1-2 is located from two
fold lines in each view, using dimensions or projection lines
that originate in a previous view. Dimensions D1 and D2
establish the elevation of the end points in the profile and
frontal view, since these points are horizontally in line in these
two views. D3 and D4 locate the end points in relation to the
F/P fold line (to the left of the profile plane), in both the frontal
and horizontal views, since these points are aligned vertically.
D5 and D6 locate each point in relation to the H/F and the F/P
fold line, since these dimensions are the distance behind the
frontal plane and will show in both the horizontal and profile
views.
A. Level and Vertical Lines
A line that is parallel to the horizontal projection plane is a
“level” line and appears true length in the horizontal view. A
level line is a horizontal line (principal line) since it is parallel
to the horizontal projection plane. In figure below the three
variations of level (horizontal) lines are illustrated. In example
(1), line 1-2 is parallel to the horizontal plane and inclined to
the frontal and profile planes. It appears true length in the
horizontal view and foreshortened in the other two views.
Example (2) shows level line line1-2 parallel to both the frontal
and horizontal projection planes and is a point view in the
profile view. Line 1-2 is true length in two principal views and
is therefore both a horizontal line and a frontal line where as in