Descriptive Geometry for Students of Engineering

t is oblique to all 'the planes of projection. A pictorial drawing of such a line is shown in Fig. 7a. The projections of the line are drawn by joining the projections of any two points in the line. For the line shown in the figure, the points most easily determined in the drawing are its intersections with the horizontal and front planes. These intersections are marked ah and W. The former, ah, has its horizontal projection coincident with the point itself, and its front projection is, of course, in the X axis at a/. Similarly the latter intersection, W, has its horizontal and front projections at bh (in the X axis) and at bf. The horizontal and front projections of the line are then drawn by joining ah with bh and af ith bt. 12. By reversing the process the intersections of the line with the planes of projection can be found when the projections of the line are given; thus in Fig. 76 the intersection of the line a b with the horizontal plane is the point, a, shown by its horizontal projection, ah, (behind the intersection of the front projection of the line with the X axis) and its front projection, a/, (in the X axis). The intersection of the same line with the front plane is the point, b, shown similarly by its projections bh and bf. When only two planes of projection are mentioned (as is the case for most problems), it is assumed the side plane is not needed. 13. Problem 1. To draw the projections of a line having given the intersections of the line wit...