Electronic theodolites and total stations

Electronic theodolites and total stations are actively used for measuring and surveying work in geodesy and design.

A bit of history

Until the beginning of the 16th century, vertical and horizontal angles were measured by several different instruments. For more effective surveying and survey work required a universal device that could combine several functions simultaneously.

A prototype of the modern theodolite of the middle of the last century was a tool called a polymer. The searchers of that time accepted him with great enthusiasm and used it throughout their work. Later versions of the middle of the XIX century laid the concept of its design.

Description of electronic theodolite

Modern theodolite has many functions to measure in its arsenal. Horizontal angles are calculated with the help of special devices - alidades and limbs. Limb - a glass circle with a scale of 360 divisions, which is fixed permanently and protected from damage. Alidade rotates around the limb along with the body of the device.

The principle of measuring and transmitting data by an electronic theodolite differs significantly from optics. All values are encrypted in binary code, so instead of degrees, minutes and seconds there are zeros or ones. Readings are transmitted using photoelectronic devices.

To increase the reliability of the instrument's readings, the design includes bubble levels and a vertical plumb line. For more accurate reading the device provides a special microscope. A characteristic difference between the electronic theodolite and its optical version is the presence of a device for recording and recording the readings in automatic mode, with their subsequent recording on the memory chip of the device.

Any theodolites used for survey or other work must be verified. If the error of the readings exceeds the established norms, it is necessary to carry out adjustment for correction. There is a state standard for the types of theodolites. Depending on the accuracy of the measurements are divided into three classes: particularly accurate, accurate and technical. The latter are mainly used for educational purposes.

The principle of the electronic theodolite

By the nature of the design there are: electronic, with a direct image, surveying, autocollimation, phototheodolites, gyrotheodolites with gyrocompass, repeat. For example, the phototheodolite has in its body a camera for precise surveying and geolocation of objects.

Electronic theodolites are devices that make it possible to greatly simplify the procedure for removing angular quantities, in comparison with fully optical devices. Such a tool allows you to work even in darkness. And the display will eliminate the error of reading. On the other hand, electronic counterparts are not without drawbacks, such as the presence of a battery, which must be periodically recharged from the network, a small range of permissible operating temperatures.

Choosing a specific model of the electronic theodolite, you should first determine the type of tasks performed. If high accuracy of measurements is not a priority, then it is quite possible to do with a class device from T15 to T30. For more accurate measurements, a device of the class from T2 to T5 is suitable. If you need unprecedented accuracy, then your choice should be stopped on the model of class T1.

It is not superfluous to know about the impact of the conditions of the survey on its final quality. For example, the presence of trees on the site may affect the reliability of the laser roulette readings . The beam is able to reflect instead of the desired object from the branches and substantially distort the data. The presence of high structures, such as towers or pipes, also affects the final result.

The housing of a quality measuring device must be made of metal, and all possible joints are rubberized to prevent dust and moisture from entering. The cheaper options from plastic parts are short-lived and often fail. A photo of the electronic digital theodolite is presented below.

Tachymeters

A more perfect version of the device is the total station. It is a symbiosis of computer and theodolite. Its cost is more expensive than usual, but manufacturability is an order of magnitude higher. It is equipped with a display and keyboard for data input, it has a built-in microprocessor for computing. Automation allows you to perform all tasks on the fly, greatly increasing the productivity of the work.

The main purpose of the tacheometer is to create terrain plans at a given scale with application of relief features. The heart of any mechanism is an integrated or external controller, which is responsible for processing the data obtained during the survey. A distinctive feature of the construction of a total station from other geodetic instruments is the modularity, which makes it possible to create a modification of the device for specific needs.

Varieties of total stations

Since most of the total stations are equipped with a distance meter based on a laser beam, the method for recording the signal distinguishes two types:

• To determine the distances, the difference in the phases of the beam is used;
• To measure the distances to the object, the time of passage of the laser beam is calculated.

To measure distances up to five kilometers, it is advisable to use reflective prisms for a laser rangefinder. With a distance of up to one kilometer, you can do without reflectors, but it should be taken into account that everything will depend on the quality of the reflecting surface of the object. The error in measuring angular quantities with a modern total station can reach a limit of one millionth of a percent or one millimeter per kilometer.

Small features of use

It is important to know that in practice such an error is almost impossible to achieve due to the influence of weather conditions and positioning errors and some human factors.

As a rule, most of the survey work is carried out at a distance of up to 300 meters. It is much less necessary to shoot at a distance of several kilometers. Modern optics allows you to measure the range up to 7500 meters.

Some modern models can be equipped with a global positioning system, to link the results of measurements to the coordinates of the map of the locality, as well as a fully automated system that does not require operator involvement.

Criterias of choice

When choosing a total station, it is necessary to determine the tasks assigned to it. For the most suitable instrument with an error of 1-2 mm per kilometer. Operational work requires the immediate transfer of data to the processing computer. For these purposes, you can choose a model equipped with a remote control and a wireless communication module, such as Wi-Fi or Bluetooth. These modifications of measuring instruments, as a rule, have the function of tracking the subject of the survey.

If there is a need to transfer the survey points to a real site, then, in this case, you need a device with a duplex data entry and transmission system.

There are cases when it is necessary to shoot a large object in three dimensions. For this purpose, tacheometer models are used that can work in the 3D scanner mode. The data of such research is transferred to the computer as a point cloud and can be further processed with the help of specialized CAD software.