Introduction
A line can be defined as the route or pathway of a point displaced from one position to another. A line can be a curved one or a straight one. A straight line is the shortest track or distance between two points. The projections of a straight line can be drawn by joining the respective projections of its end points. The position of a straight line in space may be defined by
• the location of its end points or extremities from principal planes and its true length (TL).
• the location of one of its end points and inclination of the line with the principal planes.
• the location of its end points and distance between the end projectors, etc.
Position of a Straight Line
A line in space can be in various positions w.r.t. to the principal planes of projection as shown in Table 9.1:
(i) Line parallel to both HP and VP.
(ii) Line inclined to one plane and parallel to the other
• Line inclined to the HP and parallel to the VP.
• Line inclined to the VP and parallel to the HP.
(iii) Line perpendicular to one of the planes.
• Line perpendicular to the HP and parallel to the VP.
• Line perpendicular to the VP and parallel to the HP.
(iv) Line contained by one or both of the principal planes
• Line contained by the HP.
• Line contained by the VP.
• Line contained by both HP and VP, i.e., in x-y line.
(v) Line inclined to both HP and VP.
(vi) Line contained by a profile plane (PP) or line contained by a plane, perpendicular to both HP and VP, i.e., in x-y line.
Line Parallel to Both HP and VP
Line AB, parallel to both HP and VP, is shown in Fig. 9.1 (a). Here ends A and B of the line AB are at equal distance from the HP and VP. When a line is parallel to any plane, its projections on that plane is a straight line of the same length. The elevation (front view) a'b’ and plan (top view) ab are both parallel to x-y line and their lengths represent the true length (AB of a line).
Fig. 9.1 (b) shows the orthographic projection of the line AB.
Review the options below to login to check your access.
Log in with your Cambridge Higher Education account to check access.
If you believe you should have access to this content, please contact your institutional librarian or consult our FAQ page for further information about accessing our content.