Trigonometric Levelling
Definition (1 mark)
Trigonometric levelling is a method of determining the difference in elevation between points by using measured vertical angles and horizontal distances.
When is Trigonometric Levelling Used? (2.5–3 marks)
Trigonometric levelling is used in the following situations:
1. When Points are Far Apart
- Used when the distance between points is large.
- Ordinary levelling becomes difficult and time-consuming.
2. In Rough or Hilly Terrain
- Suitable for mountainous or uneven ground.
- Direct levelling is not possible.
3. For Inaccessible Points
- Used to determine heights of objects like:
- Towers
- Hills
- Buildings
- When direct measurement is not possible.
4. For High Precision in Geodetic Surveys
- Used in large-scale surveys where curvature of the earth is considered.
5. Across Obstacles
- Useful when there are rivers, valleys, or obstacles between points.
Key Concept
- Based on trigonometry:
\text{Height} = \text{Distance} \times \tan(\theta) - Uses instruments like theodolite to measure vertical angles.
Conclusion (1 mark)
Trigonometric levelling is mainly used where direct levelling is difficult or impossible, especially for long distances, high elevations, and inaccessible points, providing a practical alternative method.
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