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 TRAVERSE COMPUTATIONS Traverse operations are conducted for mapping; for large construction projects, such as a military post or an
Figure 7-6.—Computations required to balance the level net. air base; for road railroad, and pipeline alignment; for the control of hydrographic surveys; and for many other projects. A traverse is always classified as either a closed traverse or an open traverse. A closed traverse starts and ends at the same point or at points whose relative horizontal positions are known. An open traverse ends at the station whose relative position is not previously known and, unlike a closed traverse, provides no check against mistakes and large errors. In the EA3 TRAMAN, you studied field procedures for laying out traverses. In this chapter you will study computations that are necessary for adjusting and determining the areas of traverses. Checking and Reducing Angles Begin traverse computations by checking to make sure that all the required angles (including closing angles) were turned and that the notes correctly indicate their sizes. For deflection angles, check to make sure that angles marked L or R were actually turned and have been turned in those directions. Check your sketches and be sure they agree with your field notes. Next, you reduce repeated angles to mean angles using the procedures that you learned in the EA3 TRAMAN.Checking and Reducing Distances Check to make sure that all required linear distances have been chained. Reduce slope distances when needed. If you broke chain on the slopes, you check to make sure that the sums of break distances were correctly added. Finally, you should apply standard error, tension, and temperature corrections if needed.Adjusting Angles From your study of the EA3 TRAMAN, you should recall the following three conditions for a closed traverse: (1) the theoretical or geometrical sum of the interior angles is 180° x (n – 2), n being the number of angles measured; (2) the sum of the exterior angles is 180° x (n + 2), where n = number of angles measured; and (3) the difference between the sum of the right deflection angles and the sum of the left deflection angles is 360°. Any discrepancy between one of these sums and the actual sum of the angles as turned or measured constitutes the angular error of closure.You adjust the angles in a closed traverse by distributing an angular error of closure that is within the allowable maximum equally among the angles.
Figure 7-7.—Closed traverse by deflection-angle method. Figure 7-7 shows a traverse in which one of the deflection angles was turned to the lefft, all others to the right. The sum of the right deflection angles is 444°59'. Then, by subtracting the left deflection angle (85°01'), you find that the angular error of closure is 02', which is an average of 20" per deflection angle. This average angular error of closure is then added to each right deflection angle and subtracted from each left deflection angle. After applying this adjustment to each deflection angle in this example, you find, then, that the sum of the adjusted angles to the right equals 445°00'40" and that the sum of the left angles (of which there is only one) is 85°00'40". The difference between these values is 360°00'00", as it should be.Remember that in adjusting the angles in a deflection-angle traverse, you apply the adjustments to right and left angles in opposite direction.
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