1.2.3.4.5.Figure 8-2.-Stadia hairs.measure the angle and distance from transitstationsmeasure angles from two transit stationsmeasure distances from two known pointsmeasure an angle from one station and distancefrom another stationmeasure swing offsets and range tiesAs you can well imagine, detailing by transit andtape is a time-consuming process that requires chainingmany distances and taking many level shots. This isnecessary 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 thedetails by transit and stadia.LOCATING DETAILS BYTRANSIT AND STADIAAs an EA, most of the topographic surveying thatyou will do is of a lower degree of accuracy that is wellsuited to the transit and stadia method. When you areusing this method, horizontal distances and differencesin elevation are indirectly determined by usingsubtended intervals and angles observed with a transiton a leveling rod or stadia board To explain the meaningof this, we will first discuss the principles of stadia andthen look at field procedures that are used in stadia work.Stadia Equipment Terms, and PrinciplesThe following discussion will familiarize you withthe equipment, terminology, and principles used instadia surveying. Although this discussion of stadiasurveying is included in this chapter on topography, youshould be aware that stadia can be used in any situationin which it is desired to obtain horizontal distances anddifferences in elevation indirectly. The results, though,are of a lower order of precision than is obtainable bytaping, EDM, or differential leveling. However, theresults are adequate for many purposes, such aslower-order trigonometric leveling.A thorough understanding of stadia is highlyimportant to any surveyor. You should supplement theknowledge that you gain from the following discussionby reading other books, such as Surveying Theory andPractice, by Davis, Foote, Anderson, and Mikhail.STADIA RODS.— Where sight distances do notexceed 200 feet, a conventional rod, such as aPhiladelphia rod, is adequate for stadia work. For longerdistances, however, you should use a stadia rod. Stadiarods usually have large geometric designs on them sothat they may be read at distances of 1,000 to 1,500 feetor even farther. Some rods do not have any numerals onthem. From the geometric pattern on the rod, you canobserve intervals of a tenth of a foot and sometimes ahundredth of a foot.Stadia rods generally are 10 to 15 feet long, 3 to 5inches wide, and about 3/4 inch thick. They may bemade in one piece or in sections for ease in carryingthem. Some stadia rods are flexible and maybe rolledup when not in use. Flexible rods are merely graduatedoilcloth ribbons, tacked to a board.Some examples of stadia rods are shown in chapter11 of the EA3 TRAMAN.STADIA HAIRS.— The telescope of transits (aswell as theodolites, plane-table alidades, and manylevels) is equipped with two hairs, called stadia hairs,that are in addition to the regular vertical and horizontalcross hairs. Figure 8-2 shows two types of stadia hairsas viewed through a telescope. As shown in this figure,one stadia hair is located above and the other an equaldistance below the horizontal (or middle) cross hair. Onmost equipment, the stadia hairs are not adjustable andremain equally spaced.8-3
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