the end points of line 1-2 are denoted 1H and 2H in the
horizontal views, 1F and 2F in the frontal view, and 1P and 2P
in the profile plane.
Figure 7.2 Projection of a line7.4.1 Classification of Lines in Orthographic
Projections
In orthographic projections lines can be classified based on
their parallelism with the picture planes, type and direction.
A. Classification based on Parallelism
A line that is parallel to a principal plane is called a principal
line, and is true length in the principal plane to which it is