applied), as corrected for temperature and for slope. Forthe interval between stakes 5 and 6 (where there is, asyou can see, a forward set), the horizontal distanceamounts to the standard tape length plus 0.104 foot, ascorrected for temperature and for slope. The length ofthe base line will, of course, amount to the sum of thehorizontal distances.Note that in this case the line is being measuredforward. After the forward measurement, the line isagain measured in the backward direction. If thebackward measurement varies slightly from theforward measurement, the average is taken as thelength of the base line. A large discrepancy would, ofcourse, indicate a mistake in one measurement or theother.Rather than using chaining operations to performbase line measurements, an electronic distance meter(EDM) can be used. The use of EDM equipment greatlysimplifies the measurement of base lines intriangulation. Chapter 12 of this TRAMAN gives ageneral discussion of EDMs and EDM principles.ComputationsIn triangulation of ordinary precision or higher, theobserved angles are adjusted before the lengths of thetriangle sides are computed. The most rigorous andaccurate of adjustment methods is the least squaresmethod that involves the computation of the mostprobable values of the adjusted quantities. In manyadvanced surveying textbooks, the least squares methodFigure 15-27.—-Chain of triangles.is preferred; however, calculation of the probable valuesof the unknowns involves a level of mathematics(calculus) that is beyond that required of theEngineering Aid. Therefore, in this text we will discussmore elementary adjustment procedures that, while lessaccurate than the method of least squares, yieldsatisfactory results.There are two steps in angle adjustment, calledstation adjustment and figure adjustment. Stationadjustment applies the fact that the sum of the anglesaround a point is 360°. Figure adjustment applies thefact that the sum of the interior angles of a polygon is(n – 2) x 180°, with n representing the number of sidesof the polygon.ADJUSTING A CHAIN OF TRIANGLES.— Instation adjustment you compute the sum of theTable 15-6.—Station Adjustment for Chain of Triangles, Figure 15-2715-34
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