Surveying Instruments Theodolites

Surveying Instruments Theodolites
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What Is A Theodolite?

Theodolites are electronic devices that are widely used for the measurement of vertical and horizontal angles for mapping applications, and in the construction industry. Accurate measurement of angles is essential for huge construction projects. These are important surveying instruments used in the engineering and surveying disciplines, especially in remote locations. Theodolites have been modified for numerous other specific functions in the rocket technology and meteorology. Furthermore, the accuracy of these instruments has improved significantly over the years. Though the theodolites have been used for a long period, their basic function has not changed much. The leveling systems have been improved to be more accurate and reliable, and the newer models employ infrared based technology.

Theodolite Components

A basic theodolite normally consists of a small sized telescope that is linked with mechanisms to measure horizontal and vertical angles. The theodolite telescope is fixed within perpendicular axes, namely the vertical axis and the horizontal, or trunion, axis. The theodolite is fixed on a base that can be rotated on a tripod by a leveling system. The angle to the desired point is measured by pointing the telescope to that point. The angle can be read on the telescope scale.


Types Of Theodolites

There are various kinds of theodolites:

Repeating Theodolite

Many angle readings are taken on a graduated scale. The average angle measurement is obtained by dividing the accumulated sum readings by the number of observed readings. The results of these theodolites are good. These instruments are confined for locations where the support is not stable, or space for using other such instruments is limited.

Direction Theodolites

The circle is arranged to be fixed, while the telescope is aimed on a number of signals. Readings on the circle are read for every direction. Direction theodolites are ideal instruments for triangulation.

repeating theodolites

Comparison of Theodolite And Total Station

Both the total station and theodolite are devices for the measurement of vertical and horizontal angles during engineering projects and surveying. Each has specific characteristics due to which they are used. Normally, the factors of time, expertise available, and cost will determine the use of either of these instruments. However, the major differences in these survey instruments are explained below:


A theodolite includes a suitable telescope that is fixed between the horizontal and vertical axes. The axes angle can be calculated accurately only if the operator has enough information regarding trigonometry. Furthermore, a theodolite normally needs the assistance of one person in addition the operator, to facilitate the measurement and alignment of angles. To ensure accuracy, both the operators should be able to level the tripod and the measuring post. Furthermore, they should be able to align the measuring line and the stake to obtain an accurate data. Mathematical and graphical proficiency is also required to produce the appropriate data. A theodolite is normally used for small size plots. In the modern theodolites, the reading of the vertical and horizontal circles is executed electronically by a rotary encoder. Additionally, sensors are added to allow auto-targeting and automatic measurements by using integral software. Some modern theodolites have electro-optical distance measuring tools, usually infrared, permitting simultaneous measurements of the vectors.

Total Station

A total station is considered to be a superior surveying tool compared to the theodolite due to its digital integration and all-inclusive features. A total station incorporates the functions of theodolite to determine angles and distances by an electronic distance meter. Total stations employ a combination of lasers and prisms to record digital readings of the measurements in a computer. This data can be used further analysis. Robotic total stations have been developed that can be operated remotely. However, the total stations are expensive and need not only survey expertise, but also detailed training on software. Total stations are suitable for survey requirements over large distances, particularly over difficult terrain. The results of a total station on such environments are more accurate.

theodolite comparison