The correct answer is: C. spirit levelling
Spirit levelling is a surveying method used to measure the difference in elevation between two points. It is a precise and accurate method that is often used in construction and engineering projects.
To perform spirit levelling, a surveyor will set up two levelling rods at the two points to be measured. The rods will have a spirit level vial mounted on them, which will indicate when the rods are level. The surveyor will then use a levelling staff to measure the difference in elevation between the two rods.
Spirit levelling is a reliable and accurate method for measuring elevation differences. It is often used in construction and engineering projects, as well as in other applications where precise elevation measurements are required.
Here are brief descriptions of the other options:
- Hypsometry is a method of measuring elevation by determining the height of a point above sea level. It is often used in geography and geology.
- Barometric levelling is a method of measuring elevation by using a barometer to measure the pressure of the atmosphere. It is not as accurate as spirit levelling, but it is a simpler and faster method.
- Trigonometric levelling is a method of measuring elevation by using trigonometry to calculate the distance between two points. It is a very accurate method, but it is also a complex and time-consuming method.