BeginnerTopic 20 of 112Civil & Structural
Levelling
Determines height differences using a level and staff.
In depth
A level and staff measure height differences: rise-fall or height-of-collimation methods. Sources of error: collimation, parallax, staff tilt, curvature and refraction. Closed loops check accuracy; permissible misclosure 12√K mm (K in km) for ordinary levelling.
Key points
- Backsight, foresight, intermediate sights
- Reduced level (RL)
- Benchmark
ExampleLevelling the road centreline every 20 m produces a longitudinal profile.
Levelling finds height differences accurately, which is needed for drainage, foundations and roads where levels control performance.
What is Levelling?
Determines height differences using a level and staff.
Why is it important to understand levelling?
Levelling finds height differences accurately, which is needed for drainage, foundations and roads where levels control performance.
How does a level work?
A telescope on a level gives a horizontal line of sight, and readings on a staff held at points give the height difference.
What is a benchmark?
A surveyed point with a known height that serves as the reference for other levels on a project.
How is Levelling used in practice?
Typical applications include setting the floor level of a building relative to the road, checking the fall of a drain pipe to make sure water flows and establishing the grade of a road embankment from a benchmark.
What should I learn before Levelling?
Study "Chain and tape surveying" first (topic 19 of 112 in Civil & Structural). It covers the groundwork this topic builds on.
What are the key points of Levelling?
Backsight, foresight, intermediate sights. Reduced level (RL). Benchmark.
Can you give an example of Levelling?
Levelling the road centreline every 20 m produces a longitudinal profile.
What comes after Levelling?
The next topic is "Theodolite and total station", which builds directly on this one.
How difficult is Levelling?
It is classed as Beginner in Civil & Structural (topic 20 of 112). It is an entry-level topic. It relies only on basic school mathematics and the ideas introduced earlier in this discipline.