Certainly! Levelling in surveying is the process of determining the height of one level relative to another. It’s commonly used to establish the elevation of a point relative to a reference datum or to determine a point’s elevation at a given level. Here are some key points about levelling:
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Purpose: Levelling helps establish, verify, or measure the height of specified points in relation to a datum. It serves various purposes:
- Geodesy and Mapping: Used to measure geodetic height.
- Construction: Quantifies height disparities between building objects.
- Mapping: Determines elevations of locations or variations in altitude1.
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Types of Levelling:
- Precise or Geodetic Levelling: High-accuracy levelling for geodetic purposes.
- Ordinary or Simple Levelling: Commonly used for construction and mapping.
- Other methods include differential levelling, profile levelling, cross-sectioning, reciprocal levelling, trigonometric levelling, and more.
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Levelling Procedures:
- Setting Up: Ensures equal backsight and foresight distances to avoid errors due to collimation, refraction, or earth curvature.
- Eliminating Parallax: Adjusts the eyepiece to eliminate apparent movement caused by the observer’s eye.
- Booking: Observations are recorded in level books or loose-leaf levelling sheets, including details like site, date, observer, and instrument2.
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