Local Attraction Impact on Surveying Bearings
In surveying, the back bearing (BB) of a line should ideally be 180 degrees different from its fore bearing (FB). This is represented as:
BB = FB ± 180°
However, when a station is affected by local attraction, the magnetic needle is disturbed. This disturbance causes the observed magnetic bearings (both fore and back) to be incorrect.
Effect of Local Attraction on Bearing Difference
- Local attraction introduces errors in the magnetic readings at the affected station.
- Consequently, the fundamental relationship where the back bearing is exactly 180 degrees from the fore bearing is disrupted.
- Therefore, if a station suffers from local attraction, the difference between the fore bearing and the back bearing will not be equal to 180 degrees.
This deviation from the 180-degree rule is a key indicator of local attraction affecting the observations at that specific station.
Important Questions from Compass Surveying and Theodolite
What is the difference of longitude between two places C and D from the following longitudes ?
1. Longitude of C = 46° W
2. Longitude of D = 64° W
Arrange the order of permanent adjustment of a theodolite.
1) Plate level test
2) Cross- hair ring test
3) Bubble tube adjustment test
4) Spire test
5) Collimation in azimuth test
6) Vertical circle test
Isogonic lines are the lines having the same _______.
Which one of the following statements is correct?
Which optical element's movement within a telescope typically enables internal focusing while maintaining a constant physical length of the instrument?
