Traces of Plane Figures

TRACES OF PLANE FIGURES

If a plane figure which is kept in dihedral angle is projected, it will intersect the reference planes (HP and VP) at two different lines, unless the plane is parallel to either of the reference planes.

It is to be noted that for any position of plane (parallel, inclined or perpendicular) the trace of a plane figure cannot be a plane figure since the plane figure is of negligible thickness, like thin sheet and projected to the reference planes. So the trace of a plane figure will necessarily be a straight line, length of which is decided by the position of the plane.

The line of intersection of the lamina with HP is called the horizontal trace (H.T) and the line of intersection of the plane with the VP is called the vertical trace (V.T). 

If a lamina is kept parallel to any plane (shown in Fig. 13.5 (i) ), the lamina will not intersect that plane if extended. Hence the trace of the lamina on the parallel plane is zero. (No Horizontal trace and no Vertical trace).

If a lamina is kept perpendicular to any plane (Fig. 13.5 ii), the lamina will intersect that plane if extended. Hence trace of the lamina is straight line. 

Similarly if a lamina is kept inclined to any plane (Fig. 13.5 iii and iv), the lamina will intersect that plane, if extended. Hence trace of the plane is a straight line.