Levelling – how heights are defined
Engineering surveying involves the measurement of three quantities; heights, angles and
distances.
Levelling it the process of measuring heights.
It is possible when levelling to measure heights with an accuracy of millimetres
Heights can also be measured using total stations, handheld lasers and GPS devices.
However, levelling offers an inexpensive, simple and accurate method for measuring
heights, and it is widely used in construction sites.
Any method of measuring the heights of points above or below the ground using an
agreed datum.
These datum's or reference points are present in all construction sites and has an
arbitrary height assigned to the point. Most construction sites will have several of these
benchmarks, and if they have heights based on an arbitrary datum, they are known as
Temporary Bench Marks.