The Theodolite is a telescope optical instrument, used often by topographers or by those who deal with topics related to topography, to measure the angles contained in a horizontal plane, azimuthal, and those in a vertical plane, zenith. It is that tool that perhaps some of us have seen on the streets, used to carry out geodetic and topographic surveys. It may look familiar but it's not easy to understand how it works.
Theodolite: how to use it
Taking a theodolite you notice that it is consisting of a base, an alidade and then two graduated circles, one horizontal and one vertical, respectively integral with the base or alidade and the rotation axis of the telescope.
Returning to the base of our instrument, it must be equipped with a spirit level and some screws so that those who use it can adjust the verticality of the main axis of the instrument. The alidade it is finally a sort of small and rotating rod pivoted in the center of the protractor scale that we find on the theodolite, we find this component on others as well ancient astronomical and topographical instruments.
Understanding how this tool is made, let's try to use it. Self we wish to measure azimuth angles, on the horizontal plane therefore, we must perform the first reading with the vertical circle on the left and the second with the vertical circle on the right. With these two conjugate readings the correct measurement, without errors of eccentricity and horizontality and orthogonality.
This tool is mostly used to carry out measurements during topographic surveys. The first operation to do, pre - measurement, is to check the bubble level which must reassure us on the level of precision of the topographic measurements.
On the horizontal circle they do azimuth measurements while the zenith ones are carried out on the vertical one, in any case they must be carried out several times on different areas of the azimuth circle and then calculate an average value using a rule for technicians, called Bessel's rule.
Theodolite and tacheometer
Who does not use the theodolite for work, often, it can risk confusing it with the tachymeter. This last instrument also measures distances to provide angular measurements with greater precision, the theodolite instead reaches a maximum of one to five centesimal seconds, certainly not 20 centesimal seconds of the tacheometer.
It is not a tool that you buy as a hobby or for personal passion but for work. Prices are certainly not very affordable, but it also depends on the size and characteristics of the instrument itself. 83 cm high, a theodolite with instructions for use, it can cost around 100 euros but there are models that touch or exceed 1000 euros.
The Ancient theodolite it is made as we have explained, only with less precision because over the years the materials used and the construction techniques have been improved more and more. However, if you want to look at reality without too much melancholy due to the passing of time, in many areas the theodolite is ancient by definition because almost completely replaced by Total Station, or total station.
In this "total" station, there is always a kind of theodolite but with a coupled distance meter almost always coaxially which ensures more precise measurements. In turn, the distance meter can be "ancient", that is traditional, when it needs the reflecting prism to carry out the distance measurement, or modern, laser, and then detects the distance without the need for the presence of the prism. When you have to measure distances and angles in inaccessible areas necessarily the theodolite alone is ancient and serves the laser distance meter.
In addition to the theodolite and the distance meter, in the total stations we find a small computer which automatically stores the reading of the horizontal and zenith angles and the distance, transferring everything to a fixed computer.
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