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, the measurement of vertical and horizontal angles was carried out with several different instruments. For more efficient surveying and prospecting work, a universal device was required that could combine several functions at the same time.
The prototype of the modern theodolite of the middle of the last century was an instrument called a polymeter. The prospectors of that time accepted it with great enthusiasm and used it everywhere in their work. Later versions of the mid-19th century laid the foundation for its design.
Description of the electronic theodolite
The modern theodolite has many measurement functions in its arsenal. Horizontal angles are calculated using special devices - alidade and limbus. The limb is a glass circle with a scale of 360 divisions, which is permanently fixed and protected from damage. The alidade rotates around the limbus along with the body of the device.
Principle of measurement and data transmissionelectronic theodolite differs significantly from optics. All values are encrypted in binary, so instead of degrees, minutes and seconds, there are zeros or ones. The reading is transmitted using photoelectronic devices.
To increase the reliability of the readings of the device, the design includes bubble levels and a vertical plumb line. For more accurate readings, the device provides a special microscope. A characteristic difference between an electronic theodolite and its optical version is the presence of a device for taking and recording readings in automatic mode, followed by their recording on the device's memory chip.
Any theodolites used for survey or other work must be verified. If the reading error exceeds the established norms, it is necessary to carry out adjustment for correction. There is a state standard for types of theodolites. Depending on the accuracy of the measurements, they are divided into three classes: especially accurate, precise and technical. The latter are mainly used for educational purposes.
The principle of operation of the electronic theodolite
By the nature of the design, there are: electronic, with a direct image, mine surveying, autocollimation, phototheodolites, gyrotheodolites with a gyrocompass, repeaters. For example, a phototheodolite has a camera in its body for accurate shooting and reference of geological objects.
Electronic theodolites are devices that can greatly simplify the procedure for taking angular values, compared to fully opticaldevices. This tool allows you to work even in the dark. And the presence of the display will eliminate the error of taking readings. On the other hand, electronic counterparts are not without drawbacks, such as the presence of a battery that needs to be periodically recharged from the mains, a small range of permissible operating temperatures.
Choosing a specific model of an electronic theodolite, you should first of all decide on the type of tasks to be performed. If high measurement accuracy is not a priority, then it is quite possible to get by with a class device from T15 to T30. For more accurate measurements, a device of class T2 to T5 is suitable. If you need unprecedented accuracy, then you should opt for a T1 class model.
It will not be superfluous to know about the influence of shooting conditions on its final quality. So, for example, the presence of trees in the area can affect the reliability of the readings of the laser roulette. The beam is able to reflect from the branches instead of the desired object and significantly distort the data. The presence of high structures on the site, such as towers or pipes - also affect the final result.
The case of a high-quality measuring device should be made of metal, and all possible joints should be rubberized to prevent dust and moisture from entering. Cheaper options made of plastic parts are short-lived and often fail. A photo of an electronic digital theodolite is presented below.
Total stations
A more perfect type of device is a total station. It is a kind of symbiosis of a computer and a theodolite. Its cost is more expensive than usual, but manufacturability is an order of magnitude higher. It is equipped with a display and a keyboard for data entry, has a built-in microprocessor for calculations. Automation allows you to perform all tasks on the fly, while significantly increasing productivity.
The main purpose of the tacheometer is to create terrain plans on a given scale with drawing features of the relief. The heart of any mechanism is an integrated or external controller, which is responsible for processing the data received during the survey.
A distinctive feature of the design of the total station from other geodetic instruments is its modularity, which allows you to create a modification of the device for specific needs.
Varieties of total stations
Since most total stations are equipped with a distance meter based on a laser beam, there are two types according to the method of signal registration:
- beam phase difference is used to determine distances;
- to measure the distance to an 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. At a distance of up to one kilometer, you can do without reflectors, but it should be noted that everything will depend on the quality of the reflective surface of the object. The error in measuring angular values with a modern total station can reach the limit of one millionthpercent 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 survey work is carried out at a distance of up to 300 meters. Much less often, it becomes necessary to shoot at a distance of several kilometers. Modern optics allow measuring ranges up to 7500 meters.
Some modern models can be equipped with a global positioning system for linking measurement results to the coordinates of the terrain map, as well as a fully automated system that does not require operator participation.
Selection criteria
When choosing a total station, you need to determine the tasks assigned to it. For most, a device with an error of 1-2 mm per kilometer is suitable. 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 module such as Wi-Fi or Bluetooth. These modifications of measuring instruments, as a rule, have the function of tracking the subject.
If it becomes necessary to transfer survey points to a real site, then, in this case, you need a device with a duplex system for input and data transmission.
There are times when you need to capture a large object in three dimensions. For these purposes, applytotal station models that can work in 3D scanner mode. The data of such a study are transferred to a computer in the form of a point cloud and can be further processed using specialized CAD programs.
