. Railroad construction, theory and practice; a text-book for the use of students in colleges and technical schools . Fig. a chord may be runable that a should be a multipleof D, the degree of curve, and thatthe points m and n should be oneven stations, mn =2R sin ^a. Apoint s may be located by an offsetks from the chord mn by a similarmethod to that outlined in § 60. The device of introducing thedotted curve mn having the sameradius of curvature as the other,although neither necessary noradvisable in the case shown inFig. 24, is sometimes the bestmethod of surveying around anobstacle. The off
. Railroad construction, theory and practice; a text-book for the use of students in colleges and technical schools . Fig. a chord may be runable that a should be a multipleof D, the degree of curve, and thatthe points m and n should be oneven stations, mn =2R sin ^a. Apoint s may be located by an offsetks from the chord mn by a similarmethod to that outlined in § 60. The device of introducing thedotted curve mn having the sameradius of curvature as the other,although neither necessary noradvisable in the case shown inFig. 24, is sometimes the bestmethod of surveying around anobstacle. The offset from any point on the dotted curve tothe corresponding point on the true curve is twice the ordinateto the long cord/^ as computed in § 60. 63, Modifications of location. The following methods maybe used in allowing for the discrepancies between the paperlocation ^ based on a more or less rough prehminary survey andthe more accurate instrumental location, (See § 18.) They are. 72 RAILROAD CONSTRUCTION. §63. also frequently used in locating new parallel tracks and modify-ing old tracks. a. To move the forward tangent parallel to itself a distance «,the point of curve (a.) remaining fixed. (Fig. 25.) FF=-T sin/iFy~sin J* *AV=AV + VV\The triangle BmB is isosceles and Bm=Bm. Br x B-R=00=mB = vers BmB vers A (13) /. R=R + X vers A (14) The solution is very similar in case the tangent is moved in-ward to VB\ Note that this method necessarily changes the
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