Example 28-4: Determine the azimuth of the sides of a closed traverse (Figure 28.6) from Interior Angles by making correction using interior angle adjustment ethod. Solution : Figure 28.6 shows an interior-angle closed traverse that originates at point A lying on the line PQ having a known azimuth of 42° 00' 00" as determined from a previous survey. In this traverse, point A was occupied first and an angle was observed between line PQ and traverse line AB. The angle is observed to be 18° 00' 00". After the interior angle at A was observed, points B,C,D and E were occupied and interior angles was observed by method of repetition (at least twice) at each traverse station. The algebraic sum of the interior angles (539° 58' 20") is then computed and found to be less than (2n - 4) X 90° i.e., 540° 00' 00" [column (1b) of Table 28.5]. Thus, there is an error of closure error of - 1' 40". To adjust the observed angles, this error is distributed equally (20") among all the five angles, assuming all angles are of equal weight. Since the sum of observed angles is less than (2n - 4) X 90°, 20" is added to each of the angles. Thus, the adjusted values of interior angles are determined [Column (3) of Table 28.5] Table 28.5 Adjustment of Interior Angles (Figure 28.6)
Directions for the traverse sides are reckoned using the angle QAB turned from the line of known azimuth PQ to line AB Thus, the azimuth of line AB is 42° 00' 00" + 18° 00' 00"= 62° 00' 00". The azimuths of each succeeding traverse line are then calculated by using the adjusted interior angle in Eq 28-2 and are as shown in column (3) of Table 28.6. It has been found that the observed azimuth of the starting side AB agrees with its computed value. Table 28.6 Calculation of Azimuths from Adjusted Interior Angle (Figure 28.6)
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