Traces of a line

• The trace of a line is defined as a point at which the given line, if produced, meets or intersects a plane.
• When a line meets HP, (or if necessary on the extended portion-of HP), the point at which the line meets or intersects the horizontal plane, is called horizontal trace (HT)of the line and denoted by the letter H.
• When a line meets VP (or if necessary on the extended portion of VP), the point at which the line meets or intersects the vertical plane, is called vertical trace (VT) of the line and denoted by the letter V.
• When the line is parallel to both HP and VP, there will be no traces on the said planes. Therefore the traces of lines are determined in the following positions of the lines.

Trace of a line perpendicular to one plane and parallel to the other
Since the line is perpendicular to one plane and parallel to the other, the trace of the line is obtained only on the plane to which it is perpendicular, and no trace of the line is obtained on the other plane to which it is parallel.  Figures 2 and 3 illustrates the trace of a line parallel tp0VP and perpendicular to HP and parallel to HP and perpendicular to VP respectively.

Figure 2. Trace of  line parallel to VP and perpendicular to HP

Figure 3. Trace of a line perpendicular to the VP and parallel to HP