Leveling is an essential technique in surveying that involves the measurement of height differences between different points on the surface of the Earth. It is used in a wide range of applications, such as constructing buildings, roads, and other infrastructure, as well as in topographic mapping and land development projects. In order to accurately determine the elevation of a particular location, surveyors use a variety of instruments and techniques, and also employ specific terms and concepts. In this article, we will explore the common terms used in leveling and their uses in surveying, providing a comprehensive understanding of this fundamental aspect of the field.
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Terms Used in Leveling
Leveling is an essential technique used in civil engineering to determine the difference in elevation between two points on the earth’s surface. It is crucial for various construction and surveying projects, as it ensures that structures are built at the correct height and slope. In this article, we will discuss the different terms used in leveling and their meanings.
A benchmark is a permanent and stable reference point that serves as the starting or ending point for a leveling survey. It is usually a brass or concrete monument with a known elevation established by a government agency or a professional surveyor.
2. Horizontal Line of Sight:
It is a theoretical level line between the observer’s eye and the target point. In leveling, the horizontal line of sight is assumed to be parallel to the vertical line of sight, which ensures that all the measurements are on the same horizontal plane.
A datum is a theoretical reference surface used to establish the height or elevation of points in a survey. The most commonly used datum in civil engineering is the Mean Sea Level (MSL) or the Geodetic Datum, which is chosen based on the location of the project.
4. Backsight (BS) and Foresight (FS):
Backsight is the first reading taken by the surveyor towards the benchmark. It serves as a reference for the second reading taken by the surveyor towards the point of interest, known as a foresight. By taking BS and FS readings, the level difference between the benchmark and the point of interest can be calculated.
The rod is a measuring tool used in leveling to measure vertical distances. It is usually graduated in meters or feet and is made of wood or aluminum. A leveling rod typically has two faces, one for taking readings with the level instrument and one for taking readings with the measuring staff.
6. Instrument Error:
It refers to the error introduced by the surveying instrument used in leveling. As instruments are not perfect, it is essential to determine and correct the instrument error to obtain accurate measurements.
7. Line of Collimation:
It is a line joining the cross-hairs of the telescope of the level instrument. The line of collimation remains horizontal when the instrument’s horizontal axis is level, which ensures that all the measurements are on the same horizontal plane.
8. Intermediate Sighting:
It is a reading taken by the surveyor between two primary points to increase the accuracy of the measurements. It reduces the effect of errors caused by sloping ground or uneven surfaces.
9. Rise and Fall Method:
It is a closed loop method of leveling where the surveyor takes readings in both forward and backward directions, starting and ending at the benchmark. The total of the readings in the forward direction is called the rise, while the total of the readings in the backward direction is called the fall.
10. Change Point:
Change points are used in the rise and fall method to eliminate the errors caused by uneven terrain. They are selected points where the gradient of the surface changes drastically, and readings are taken from these points to obtain more accurate measurements.
In conclusion, leveling is a crucial technique in civil engineering, and understanding these terms is essential to carry out accurate leveling surveys. As with any surveying method, proper training and experience are necessary to produce reliable results. It is also important to adhere to safety protocols and use calibrated instruments to ensure precise and error-free measurements.
In conclusion, the terms used in leveling are essential in the field of surveying as they provide precise measurements and accurate calculations for various construction and engineering projects. From benchmark and datum to vertical control and trigonometric leveling, each term serves a specific purpose in achieving high levels of precision and accuracy in surveying. It is crucial for surveyors to have a thorough understanding of these terms and their uses to ensure the success and safety of construction projects. By familiarizing oneself with these terms, surveyors can confidently navigate through different types of terrain and obstacles, ultimately producing reliable and efficient results. In summary, understanding the various terms used in leveling is crucial in creating a solid foundation for successful surveying work.