Projection on Auxiliary Inclined Plane
Point P is situated in first quadrant at a distance n from VP. An auxiliary planeAIP is set up perpendicular to VP and inclined at θ to HP. The point P is projected on VP, HP and AIP.
p' is the projection on VP, p is the projection on HP and P1 is the projection on AIP.
Since the point is at a distance n from VP, both p and p1 are at a distance n above the XY and X1Y1 lines, respectively
Figure 6. Orthographic projection of point P by auxiliary projection on AIP.
HP is now rotated by 90° about XY line to bring it in plane with VP, as shown in figure 7(a). After the HP lies in-plane with VP, the AIP is rotated about the X1Y1, line, so that it becomes in-plane with that of both HP and VP.
p and p’ lie on a vertical projector perpendicular to the XY line, and p’ and p1 lie on a projector perpendicular to the X1Y1 line which itself is inclined at θ to XY line.
Figure 7. Orthographic projection of point P by auxiliary projection on AIP.