Understanding the Role of Back Sight and Fore Sight During Levelling

The surveying process involves taking into account the measurement of distances, angles, and elevations. During the levelling process, back sight and fore sight are two crucial elements that need to be taken into consideration. Understanding the role of each is essential for accurate results. In this article, we'll be exploring the importance of back sight and fore sight during levelling.

What is Levelling?

Levelling is the process of determining the height of a point relative to a reference point. It is a critical part of surveying and is used in many different applications. Levelling can help determine the location of different points, such as the height of the ground to create a contour map, the height of the building to determine the proper drainage, and more.

What is Back Sight and Fore Sight?

Back sight and fore sight are two elements of the levelling process. Back sight is the measurement taken from a higher point to a lower point. Fore sight is the measurement taken from a lower point to a higher point. During levelling, the back sight is first taken, followed by the fore sight, and the difference between the two measurements is used to calculate the height of the point being measured.

For example, if the back sight is measured at 1.7 meters and the fore sight is measured at 1.4 meters, then the difference between the two measurements is 0.3 meters. This means that the point being measured is 0.3 meters higher than the reference point.

Why is it Important to Calculate Back Sight and Fore Sight During Levelling?

It is important to calculate back sight and fore sight during levelling because it helps to accurately measure the height of a point relative to the reference point. Without taking into account the difference between back sight and fore sight, it would be impossible to accurately measure the height of a point.

It is also important to note that during levelling, if the back sight is more than the fore sight, then the point being levelled is higher than the reference point. Conversely, if the fore sight is more than the back sight, then the point being levelled is lower than the reference point.

Conclusion

In conclusion, understanding the role of back sight and fore sight during levelling is essential for accurate results. During levelling, back sight is the measurement taken from a higher point to a lower point, while fore sight is the measurement taken from a lower point to a higher point. It is important to note that during levelling, if the back sight is more than the fore sight, then the point being levelled is higher than the reference point.