Question
Download Solution PDFFollowing are the observations made on a closed traverse.
|
Line |
Fore Bearing |
Back Bearing |
|
AB |
10° 20' |
190° 20' |
|
BC |
155° 30' |
336° 30' |
|
CA |
290° |
112° |
The total error is ___________.
Answer (Detailed Solution Below)
Detailed Solution
Download Solution PDFConcept:
Local Attraction:
- Local attraction is the amount of deviation of the magnetic needle of the compass under the influence of the external attractive forces caused due to the presence of magnetic materials, such as iron pipes, etc.
- If the difference between the fore and back bearings of the line is 180° both the end stations are considered to be free from local attraction, provided the compass is devoid of any instrumental errors.
- If the difference is not 180°, it is suggesting presence of local attraction at either or both of the stations.
Calculation:
Difference between back bearing and fore bearing for all stations is shown in the following table:
| Line | Fore Bearing | Back bearing | Value of difference between BB and FB |
| AB | 10° 20' | 190° 20' | 180° 00' |
| BC | 155° 30' | 336° 30' | 181° 00' |
| CA | 290° | 112° | 178° 00' |
As the difference between BB and FB of line is exactly 180° 00', so station A and B are free from local attraction.
Correction for station C
FB of line BC = 155° 30' which is correct.
Hence, correct BB of line BC = 155° 30' + 180° 00' = 335° 30'
So, error at A = 336° 30' - 335° 30' = +1° 00'
Correction for station A
Correct FB of line CA = 290° 00' - 1° 00' = 289° 00'
Hence, correct BB of line CA = 289° 00' - 180° 00' = 109° 00'
Hence total error = 112° 00' - 109° 00' = +3° 00'.
Last updated on May 28, 2025
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