Electronic theodolites and total stations are actively used for measuring and surveying in geodesy and design.
A bit of history
Until the beginning of the 16th century, vertical and horizontal angles were measured with several different instruments. For more effective surveying and survey work, a universal device was required that could combine several functions at the same time.
The prototype of the modern theodolite of the sample 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 functions to measure in its arsenal. Horizontal angles are calculated using special tools - alidade and limb. A limb is a glass circle with a scale of 360 divisions, which is fixed permanently and protected from damage. Around the limb, the alidad rotates along with the body of the device.
The principle of measuring and transmitting data by electronic theodolite is significantly different from optics. All values are encrypted in binary, so instead of degrees, minutes and seconds, there are zeros or ones. Reading is transmitted using photoelectronic devices.
To increase the reliability of the instrument readings, bubble levels and a vertical plumb line are included in the design. For a more accurate reading, the device provides a special microscope. A characteristic difference between the electronic theodolite and its optical version is the availability 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 surveying or other work must be verified. If the error of the readings exceeds the established standards, it is necessary to carry out adjustment for correction. There is a state standard for the types of theodolites. Depending on the accuracy, the measurements are divided into three classes: extremely accurate, accurate and technical. The last of them 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, surveying, auto-collimation, photo theodolites, gyrotheodolites with gyrocompass, repeat. For example, phototheodolite has a camera in its body for accurate shooting and geological objects.
Electronic theodolites are devices that can greatly simplify the procedure for taking angular values, compared with fully optical devices. Such a tool allows you to work even in dark conditions. And the presence of a 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, and a small range of permissible operating temperatures.
Choosing a specific model of electronic theodolite, you should first determine the nature of the tasks performed. If high measurement accuracy is not a priority, then it is quite possible to get by with a device of class T15 to T30. For more accurate measurements, a class device from T2 to T5 is suitable. If unprecedented accuracy is needed, then you should stop your choice on a model of class T1.
It will not be superfluous to know about the influence of the shooting conditions on its final quality. So, for example, the presence of trees on the site can affect the accuracy of the laser roulette. A ray is able, instead of the desired object, to bounce off branches and significantly distort data. The presence on the site of tall structures, 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. Cheaper options made of plastic parts are short-lived and often fail. A photo of the electronic digital theodolite is presented below.
Tacheometers
A more advanced version of the device is a total station. It is a kind of symbiosis of the computer and theodolite. Its cost is more expensive than usual, but manufacturability is an order of magnitude higher. Equipped with a display and 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 total station is to create terrain plans on a given scale with the application of terrain features. The heart of any mechanism is an integrated or external controller that is responsible for processing the data obtained during the shooting process.
A distinctive feature of the design of the total station from other geodetic instruments is 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 of signal detection methods:
- to determine the distance, the difference in the phases of the beam is used;
- to measure the distance to the object, the transit time 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 by a modern total station can reach the limit of one millionth of a percent or one millimeter per kilometer.
Minor Usage Features
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. Much less often there is a need to shoot at a distance of several kilometers. Modern optics allows you to measure ranges up to 7500 meters.
Some modern models can be equipped with a global positioning system to link the measurement results to the coordinates of the terrain map, as well as a fully automated system in which the operator does not need to be involved.
Criterias of choice
Choosing a total station, you need to determine the tasks assigned to it. For most, a device with an accuracy 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 there is a need to transfer survey points to a real site, then, in this case, you need a device with a duplex data input and transmission system.
There are times when it is necessary to shoot a large object in three dimensions. For these purposes, models of total stations are used, which are able to work in the mode of a three-dimensional scanner. 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.