Traces of a line inclined to both the planes
Figure 6 shows the Vertical trace (V) and Horizontal Trace (H) of Line AB inclined at q  to HP and Φ  to VP.
The line when extended intersects HP at H, the horizontal trace, but will never intersect the portion of VP above XY line, i.e. within the portion of the VP in the 1^st quadrant. Therefore VP is extended below HP such that when the line AB is produced it will intersect in the extended portion of VP at V, the vertical trace.
In this case both horizontal trace (H) and Vertical Trace (V) of the line AB lie below XY line.

Figure 6  Vertical trace and horizontal trace of line AB which is inclined to both vertical plane and horizontal plane.