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Vertical Control - 14071_154
STADIA INTERVAL - 14071_156

Engineering Aid 2 - Intermediate Structural engineering guide book
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1. 2. 3. 4. 5. Figure 8-2.-Stadia hairs. measure the angle and distance from transit stations measure  angles  from  two  transit  stations measure distances from two known points measure an angle from one station and distance from  another  station measure swing offsets and range ties As you can well imagine, detailing by transit and tape is a time-consuming process that requires chaining many distances and taking many level shots. This is necessary when a high degree of accuracy is required. However,  for  lower-precision  (third  and  fourth  order) surveys, a less time-consuming method is to locate the details by transit and stadia. LOCATING DETAILS BY TRANSIT AND STADIA As  an  EA,  most  of  the  topographic  surveying  that you will do is of a lower degree of accuracy that is well suited to the transit and stadia method. When you are using this method, horizontal distances and differences in   elevation   are   indirectly   determined   by   using subtended intervals and angles observed with a transit on a leveling rod or stadia board To explain the meaning of this, we will first discuss the principles of stadia and then look at field procedures that are used in stadia work. Stadia Equipment Terms, and Principles The  following  discussion  will  familiarize  you  with the  equipment,  terminology,  and  principles  used  in stadia surveying. Although this discussion of stadia surveying is included in this chapter on topography, you should be aware that stadia can be used in any situation in  which  it  is  desired  to  obtain  horizontal  distances  and differences in elevation indirectly. The results, though, are of a lower order of precision than is obtainable by taping, EDM, or differential leveling. However, the results  are  adequate  for  many  purposes,  such  as lower-order  trigonometric  leveling. A  thorough  understanding  of  stadia  is  highly important to any surveyor. You should supplement the knowledge that you gain from the following discussion by reading other books, such as  Surveying  Theory  and Practice, by Davis, Foote, Anderson, and Mikhail. STADIA RODS.— Where sight distances do not exceed  200  feet,  a  conventional  rod,  such  as  a Philadelphia rod, is adequate for stadia work. For longer distances, however, you should use a stadia rod. Stadia rods  usually  have  large  geometric  designs  on  them  so that they may be read at distances of 1,000 to 1,500 feet or even farther. Some rods do not have any numerals on them. From the geometric pattern on the rod, you can observe intervals of a tenth of a foot and sometimes a hundredth  of  a  foot. Stadia rods generally are 10 to 15 feet long, 3 to 5 inches wide, and about 3/4 inch thick. They may be made in one piece or in sections for ease in carrying them.  Some  stadia  rods  are  flexible  and  maybe  rolled up when not in use. Flexible rods are merely graduated oilcloth ribbons, tacked to a board. Some examples of stadia rods are shown in chapter 11  of  the  EA3  TRAMAN. STADIA HAIRS.— The telescope of transits (as well as theodolites, plane-table alidades, and many levels) is equipped with two hairs, called stadia  hairs, that are in addition to the regular vertical and horizontal cross hairs. Figure 8-2 shows two types of stadia hairs as viewed through a telescope. As shown in this figure, one stadia hair is located above and the other an equal distance  below  the  horizontal  (or  middle)  cross  hair.  On most equipment, the stadia hairs are not adjustable and remain  equally  spaced. 8-3







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