Descriptive geometry . 18 DESCRIPTIVE GEOMETRY 25. Case 2. When the line is inclined toV and H and is parallel to P. CoNSTEUCTiON. Fig. :. If the given lineis parallel to P, its vertical and horizontaltraces cannot be determined by the abovemethod, since the projections of the line areperpendicular to the ground line; hence, aprofile projection of the line is T^ Fig. 54. Let it be required to determine the verticaland horizontal traces of the line ab. P isassumed at will and is indicated by HP andVP. Determine a^-h^^ the profile projection ofthe line (Art. 21, page 14), by revol
Descriptive geometry . 18 DESCRIPTIVE GEOMETRY 25. Case 2. When the line is inclined toV and H and is parallel to P. CoNSTEUCTiON. Fig. :. If the given lineis parallel to P, its vertical and horizontaltraces cannot be determined by the abovemethod, since the projections of the line areperpendicular to the ground line; hence, aprofile projection of the line is T^ Fig. 54. Let it be required to determine the verticaland horizontal traces of the line ab. P isassumed at will and is indicated by HP andVP. Determine a^-h^^ the profile projection ofthe line (Art. 21, page 14), by revolving Pabout VP as an axis until it coincides with V. That portion of P which before revolutionwas in 3Q now falls below GiL and to theright of VP \ that portion which was in 4Qfalls below GrL and to the left of VP\ thatportion which was in i ^ falls above CrL andto the left of HP. Thus the profile projec-tion of the line, when continued, indicatesthat the line passes through 3Q into 2§ atpoint d, dp being the profile projection of thehorizontal trace. Likewise the line passesfrom SQ into 4^ at point c, c^ being the profileprojection of the vertical trace. Counter-revolve P to its original position and obtaind^ and c?^, which are the horizontal and verticalprojections of the horizontal trace, and c^ andc^ which are the vertical and horizontal pro-jections of the v
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