Microsoft Word - lecnote_fm_engineering drawing

parallel. Since there are three principal planes of projection,
there are three principal lines: horizontal, frontal and profile.
♦ A horizontal line: is a principal line which is parallel to
the horizontal plane and appears true length in the
horizontal view.
♦ A frontal line: is a principal line which is parallel to the
frontal plane and appears true length in the frontal
view.
♦ A profile line: is a principal line which is parallel to the
profile plane and appears true length in the profile
view.

(a) Horizontal line (b) Frontal line (c) Profile line

Figure 7.3 Types of principal lines

Besides the above definitions, the following terms are used to
describe lines according to the direction and type.

B. Classification Based on Direction

♦ Vertical line: A vertical line is perpendicular to the

horizontal plane, and appears true length in the frontal