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DIRECTION OF EDM MEASURED LINES - 14071_262
Figure 12-4.Slope reduction using vertical angle and slope distance.

Engineering Aid 2 - Intermediate Structural engineering guide book
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Figure  12-2.—Electromagnetic  distance-measuring  equipment in use. REDUCTION OF SLOPE DISTANCE As you learned in the EA3 TRAMAN, to reduce the slope distance of a line to horizontal distance, you need to know either the vertical angle of the line measured from  the  instrument  or  the  difference  in  elevation between the ends of the line. With that information you can use the equations that you studied in chapter 12 of the EA3 TRAMAN to reduce the slope distance. As applied  to  chaining  or  transit-tape  operations,  the calculations are simple; however, as applied to EDM operations, the procedures are frequently a little more complicated, as you will see below. The methods of slope reduction that we will discuss in this chapter should be used only for slope distances that are less than 2 miles in length or for observed vertical angles that are less than 5 degrees. For a discussion of slope reduction when distances of over 2 miles or vertical angles greater than  5  degrees  are  encountered,  you  should  study commercial  publications,  such  as  Surveying  Theory  and Practice, by Davis, Foote, Anderson, and Mikhail. Slope Reduction Using the Vertical Angle When the slope distance and the vertical angle are obtained  from  separate  setups  of  an  EDM  and  a theodolite,  additional  information  is  required  for reducing the slope distance. This information includes the  heights  above  the  ground  (h.i.)  of  the  EDM transmitter and the reflector or remote unit, the h.i. of Figure  12-3.—An  electro-optical  distance-measuring  instrument  (Geodimeter). 12-3







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