The essentials of descriptive geometry . end view of the object shown inFig. 22. 23. Draw the plan, elevation, and right end view of the object shown inFig. 23. 24. Draw a plan, elevation, and both end views of the object shown inFig. 24. CHAPTER III ASSUMPTION OF POINTS AND LINES 15. In order to study the relation of various points and lineswhich collectively form the representation of an object, and tosolve problems concerning these elements of the representation,there must be a method of designating points and lines, and therelation that these pointsand lines have to theplanes of projection
The essentials of descriptive geometry . end view of the object shown inFig. 22. 23. Draw the plan, elevation, and right end view of the object shown inFig. 23. 24. Draw a plan, elevation, and both end views of the object shown inFig. 24. CHAPTER III ASSUMPTION OF POINTS AND LINES 15. In order to study the relation of various points and lineswhich collectively form the representation of an object, and tosolve problems concerning these elements of the representation,there must be a method of designating points and lines, and therelation that these pointsand lines have to theplanes of projection mustbe known. In drafting a point isalmost never designatedby a letter, but in descrip-tive geometry it has beenfound convenient to indi-cate points and lines bythis means. A point inspace is indicated by thecapital letter, as A, B, C,etc., and its projections areindicated by the corre-sponding small letter, asa, b, c, etc.; a, b, c, beingused to indicate the planview of the point and a,b, c, etc., being usedto indicate its Fig. 25. Thus: the plan view of the point A is a, and its elevation is a,and when the point A is referred to it means the actual pointin space. The line MN means a line in space whose plan viewis mn and whose elevation is mn. 22 ESSENTIALS OF DESCRIPTIVE GEOMETRY The relation that a point or a line in space has to the planes ofprojection may be discovered from its projections. In Fig. 25is shown the plan and elevation of a hexagonal pyramid one ofwhose edges is OM. Now the plan view of the point O is o andits elevation is o, and an inspection of the figure will show thatthe distance o is from the G. L. is the distance that 0 is from theV plane; and the distance o is from the G. L. is the distancethat 0 is from H. It is also to be seen that since o is above theG. L. the point in space is behind V, and since o is belowthe G. L. the point in space is below H. Therefore, from thedrawing it may be found that the point O lies in the third quad-rant, a
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