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Base  Line  Measurement - 14071_369
ADJUSTING   A   CHAIN   OF   QUADRILATERALS

Engineering Aid 2 - Intermediate Structural engineering guide book
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applied), as corrected for temperature and for slope. For the interval between stakes 5 and 6 (where there is, as you can see, a forward set), the horizontal distance amounts to the standard tape length plus 0.104 foot, as corrected  for  temperature  and  for  slope.  The  length  of the base line will, of course, amount to the sum of the horizontal  distances. Note that in this case the line is being measured forward. After the forward measurement, the line is again  measured  in  the  backward  direction.  If  the backward   measurement   varies   slightly   from   the forward  measurement,  the  average  is  taken  as  the length of the base line. A large discrepancy would, of course,  indicate  a  mistake  in  one  measurement  or  the other. Rather  than  using  chaining  operations  to  perform base  line  measurements,  an  electronic  distance  meter (EDM) can be used. The use of EDM equipment greatly simplifies   the   measurement   of   base   lines   in triangulation.  Chapter  12  of  this  TRAMAN  gives  a general discussion of EDMs and EDM principles. Computations In triangulation of ordinary precision or higher, the observed angles are adjusted before the lengths of the triangle sides are computed. The most rigorous and accurate of adjustment methods is the  least squares method  that  involves  the  computation  of  the  most probable values of the adjusted quantities. In many advanced  surveying  textbooks,  the  least  squares  method Figure  15-27.—-Chain  of  triangles. is preferred; however, calculation of the probable values of  the  unknowns  involves  a  level  of  mathematics (calculus)   that   is   beyond   that   required   of   the Engineering Aid. Therefore, in this text we will discuss more elementary adjustment procedures that, while less accurate  than  the  method  of  least  squares,  yield satisfactory  results. There are two steps in angle adjustment, called station adjustment and figure adjustment. Station adjustment applies the fact that the sum of the angles around a point is 360°. Figure adjustment applies the fact that the sum of the interior angles of a polygon is (n – 2) x 180°, with n representing the number of sides of  the  polygon. ADJUSTING A CHAIN OF TRIANGLES.— In station  adjustment  you  compute  the  sum  of  the Table  15-6.—Station  Adjustment  for  Chain  of  Triangles,  Figure  15-27 15-34







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