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Figure 3.3

Level line: horizontal, frontal and profile line.
Parallel to Π 1 – frontal projection (on Π 2) is a line, parallel to x,
horizontal projection (on Π 1) is a line, inclined to axis.
profile projection (on Π 3) is a line, parallel to y 3.
Parallel to Π 2 – frontal projection (on Π 2) is a line, inclined to axis,
horizontal projection (on Π 1) is a line, parallel to x,
profile projection (on Π 3) is a line, parallel to z.
Parallel to Π 3– frontal projection (on Π 2) is a line, perpendicular to x,
horizontal projection (on Π 1) is a line, perpendicular to x,
profile projection (on Π 3) is a line, inclined to axis.
Perpendicular to one of projection planes and parallel to two others is called (projection line):
horizontal-projecting, frontal-projecting and profile-projecting line (Fig. 3.4 ).

Figure 3.4

Perpendicular to Π 1 – frontal projection (on Π 2) is a line, perpendicular to x,
horizontal projection (on Π 1) is a point,
profile projection (on Π 3) is a line, perpendicular to y 3.
Perpendicular to Π 2 – frontal projection (on Π 2) is a point,
horizontal projection (on Π 1) is a line, perpendicular to x,
profile projection (on Π 3) is a line, perpendicular to z.
Perpendicular to Π 3– frontal projection (on Π 2) is a line, parallel to x,
horizontal projection (on Π 1) is a line, parallel to x,
profile projection (on Π 3) is a point.
Inclined to all projection planes – all projections are inclined to axis (or general provision)
(Fig.3.1, 3.2).
If a line is perpendicular to a plane, its projection on the plane is a point. A line segment
parallel to a plane projects in its true length on the plane.
A vertical (horizontal-projecting) line projects as a point on the Π 1 –plane (Fig. 3.5). A
horizontal line segment appears in true length in the top view (on the Π 1 –plane) (Fig. 3.6). The
angle between the horizontal projection, A 1 B 1, and x is the true angle between line AB and the
vertical (frontal) plane. A frontal line is defined as a line parallel to the Π 2-plane (Fig. 3.7). The
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