Traces of a line inclined to one plane and parallel to the other
When the line is inclined to one plane and parallel to the other, the trace of the line is obtained only on the plane to which it is inclined, and no trace is   obtained on the plane to which it is parallel. Figure 4 shows the horizontal trace of line AB which is in lined HP and parallel to VP

Figure 4 Horizontal trace of line AB

Figure 5 shows the vertical trace of line AB which is inclined to VP and parallel to HP

Figure 5 Vertical  trace of line AB