In leveling operation :a)The first sight on any change point is a bac...
a) the first sight taken on changing point is foresight, not back sight.
b) the second sight on any changing point is back sight, not foresight.
c) line commences with a backsight and ends with a foresight.
Before shifting the instrument, the last sight is foresight which is taken on change point. After shifting the instrument, the first sight taken is taken on the same change point, i.e., back sight.
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In leveling operation :a)The first sight on any change point is a bac...
Explanation:
In leveling operation, the line commences with a backsight and closes with a foresight. This means that the correct answer is option 'D'.
Let's understand the terms backsight and foresight in more detail:
- Backsight: It is the first sight taken on a change point. It is taken on a benchmark or a point of known elevation to determine the elevation of the instrument station. It is also known as a turning point or a bench mark.
- Foresight: It is the second sight taken on a change point. It is taken on a point whose elevation is to be determined. It is also known as a station point.
Now, let's understand why the line commences with a backsight and closes with a foresight:
- The backsight is taken on a benchmark or a point of known elevation to determine the elevation of the instrument station. This is necessary to establish a reference point for all future measurements.
- After the backsight is taken, the instrument is moved forward to the next station point. The foresight is then taken on this point to determine its elevation.
- This process is repeated for all the station points along the line until the survey is completed.
- Finally, the line is closed by taking a foresight on the benchmark or the starting point. This ensures that the measurements are accurate and any errors are corrected.
Therefore, in leveling operation, the line commences with a backsight and closes with a foresight.