A: Plane surface parallel to one plane and perpendicular to the other two
Consider A triangular lamina placed in the first quadrant with its surface parallel to VP and perpendicular to both HP and left PP. The lamina and its projections on the three projection planes are shown in figure 1.
a'b'c' is the front view, abc the top view and a’’b’’c’’ the side view
Since the plane is parallel to VP , the front view a'b'c' shows the true shape of the lamina. Since the lamina is perpendicular to both HP and PP, the top view and side views are seen as lines.
Figure 1. Projections of a triangular lamina on the projection planes
After projecting the triangular lamina on VP, HP and PP, both HP and PP are rotated about XY and X1Y1 lines, as shown in figure 2, till they lie in-plane with that of VP
Figure 2. Rotation of PP and HP after projection.
The orthographic projections of the plane, shown in figure 3 can be obtained be the following steps.
Draw XY and X1Y1 lines and mark HP, VP and left PP. Draw the triangle a'b'c' in true shape to represent the front view at any convenient distance above the XY line. In the top view the triangular lamina appears as a lineparallel to the XY line. Obtain the top view acb as a line by projecting from the front view at any convenient distance below the XY line.