Levelling is a fundamental technique used in surveying to determine the elevation of points on the
Earth's surface relative to a reference point or benchmark. It involves the measurement of vertical
distances or elevations to establish level or flat planes. Here is a detailed summary of the definitions and
principles of levelling:
Definitions:
Elevation: Elevation refers to the vertical height of a point above or below a reference level, usually
expressed in units such as meters or feet. It is a crucial parameter in construction, engineering, and
mapping, as it provides information about the relative heights of different points on the Earth's surface.
Benchmark: A benchmark is a fixed point with a known elevation that serves as a reference for levelling.
It is typically a permanent marker or point with a known elevation, established by a recognized authority
or surveyor. Benchmarks are used as reference points for levelling measurements and to ensure the
accuracy and consistency of elevation data.
Height of Instrument (HI): The height of instrument (HI) is the elevation of the line of sight of the leveling
instrument above the benchmark or reference point. It is used as a starting point for measuring
elevations of other points during a levelling survey.
Backsight (BS): The backsight (BS) is the first levelling measurement taken from the benchmark to the
leveling instrument. It is used to establish the height of instrument (HI) and serves as a reference for
subsequent measurements.
Foresight (FS): The foresight (FS) is the levelling measurement taken from the leveling instrument to the
point whose elevation is being determined. It is used to measure the height difference between the
instrument and the point, and is added or subtracted from the height of instrument (HI) to determine
the elevation of the point.
Principles of Levelling:
Level Surface: The fundamental principle of levelling is that the line of sight of the leveling instrument is
Earth's surface relative to a reference point or benchmark. It involves the measurement of vertical
distances or elevations to establish level or flat planes. Here is a detailed summary of the definitions and
principles of levelling:
Definitions:
Elevation: Elevation refers to the vertical height of a point above or below a reference level, usually
expressed in units such as meters or feet. It is a crucial parameter in construction, engineering, and
mapping, as it provides information about the relative heights of different points on the Earth's surface.
Benchmark: A benchmark is a fixed point with a known elevation that serves as a reference for levelling.
It is typically a permanent marker or point with a known elevation, established by a recognized authority
or surveyor. Benchmarks are used as reference points for levelling measurements and to ensure the
accuracy and consistency of elevation data.
Height of Instrument (HI): The height of instrument (HI) is the elevation of the line of sight of the leveling
instrument above the benchmark or reference point. It is used as a starting point for measuring
elevations of other points during a levelling survey.
Backsight (BS): The backsight (BS) is the first levelling measurement taken from the benchmark to the
leveling instrument. It is used to establish the height of instrument (HI) and serves as a reference for
subsequent measurements.
Foresight (FS): The foresight (FS) is the levelling measurement taken from the leveling instrument to the
point whose elevation is being determined. It is used to measure the height difference between the
instrument and the point, and is added or subtracted from the height of instrument (HI) to determine
the elevation of the point.
Principles of Levelling:
Level Surface: The fundamental principle of levelling is that the line of sight of the leveling instrument is
