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AIRFIELD  SURVEYS - 14070_223
OFFSHORE LOCATION BY CHAINING - 14070_225

Engineering Aid 1 - Advanced Structural engineering guide book
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triangle  CBD,  tan B =   1,250/10,000,  or  0.125000; therefore, angle  B measures 7°7´30´´. Determining the distance  from  the  dotted  line  to  the  edge  of  the approach  zone  at  any  station  is  similarly  a  simple right-triangle  solution.  Suppose  that  AB is  located  at station 0 + 00. Then at station 1 + 00, the distance from  the  dotted  line  to  the  edge  of  the  approach  zone is 100 tan 7°7´30´´, or 12.5 feet; therefore, the distance between  the  center  line  and  the  edge  of  the  approach zone at this station is 750 + 12.5, or 762.5 feet. To check for obstructions, you must setup a transit at  the  narrow  end  of  the  approach  zone,  set  the telescope at a vertical angle equal to the one that the glide  plane  makes  with  the  horizontal,  and  take observations  over  the  whole  approach  zone,  as indicated in figure 10-27. Determining the vertical angle is a simple right-triangle solution. If the glide angle is 50:1, then the tangent of the vertical angle is 1/50, or 0.020000, and the angle measures 1°8´45´´. Figure  10-27  shows  how  the  exact  vertical location of the glide plane varies with the character of the surface of the end zone. WATERFRONT  SURVEYS Under some circumstances it is possible to chain distances  over  the  water;  however,  it  is  usually  more Figure  10-27.—Approach  clearance  for  different  types  of  end  zones. 10-26







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