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Total Station

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A Total Station is one of the major survey testing equipment, more precisely, an optical instrument that serves many purposes in surveying. Know about Total Station and its mechanical operation, function, application and features.

What is Total Station?
A total station is an electronic optical instrument widely used in modern surveying. The total station surveying instrument is a combination of an electronic theodolite (transit); an electronic distance meter (EDM), which is a measuring device to read distances; and software running on an external computer. The modern versions of surveying total stations called robotic total stations let the user control the instrument from a distance with the help of a remote control.

Features of Total Station
Total station manufacturers develop the instrument by keeping in view the maximun possible convenience of work for users. The designs of a total station is created for measuring slant distances, horizontal and vertical angles and elevations in topographic and geodetic works, tacheometric surveys, as well as for solution of application geodetic tasks. Most of the survey total stations have many of the following features:

Most of the total stations are mounted on a tripod and leveled before use.
They consist of a mounting bracket that includes aids for aiming the instrument.
Most total stations use a purpose-built glass prism mounted on a pole of known height. This acts as the reflector for the EDM signal, and can measure distances out to a few kilometers.
The prism is mounted so that its reflection point is aligned with the center of the pole on which it has been mounted.
Most modern total station instruments measure angles by means of electro-optical scanning of extremely precise digital bar-codes etched on rotating glass cylinders or discs within the instrument.
These survey instruments also include a simple calculator to figure the location of points sighted. The calculator can perform the necessary trigonometric functions.
These stations also include a data recorder, which reduce chances of error and eliminates manual data recording.
High-efficiency electronic tacheometer (a type of theodolite) is highly automated for rapid measurements during surveys.

Working of Total Station
The major operations that are conducted using total staions include determination of coordinates; measurement of angles and distance; and data processing.

Coordinates Determination by Total Station
A total station determines coordinates of an unknown point relative to a known coordinate by establishing a direct line of sight between the two points. Angles and distances are measured from the total station to points under survey, and the coordinates of surveyed points relative to the total station position are calculated using trigonometry and triangulation. Some total stations have a Global Navigation Satelite System (GNSS) which doesn't require a direct line of sight to determine coordinates.

Angle Measurement by Total Station
Most of the modern total stations have digital bar-codes on rotating glass cylinders or discs that are installed within the instruments. Angle measurement is done through electro-optical scanning of these digital bar-codes. Quality total stations can measure angles to 0.5 arc-second. Cheap models of total stations like the construction grade total stations do not have such level of accuracy and can usually measure angles to 5 or 10 arc-seconds.

Distance Measurement by Total Station
A total station has a small solid-state emitter within its optical path. They generate modulated microwave or infrared signals that are reflected by a prism reflector or the object under survey. The computer installed in the total staion reads the modulation pattern in the returning signal. The distance is thus determined by emitting and receiving multiple frequencies and determining the integer number of wavelengths to the target for each frequency. A well built total station can measure distances with an accuracy of approximately 1.5 millimetres + 2 parts per million over a distance of up to 1,500 metres. The total stations that do not carry reflectors are capable of measuring distances to any object which light in color, to a few hundred meters.

Data Processing by Total Station
The data recorded by the instrument may be downloaded from the theodolite to a computer and application software generates a map of the surveyed area. Many advanced models of total station have internal electronic data storage to record distance, horizontal angle, and vertical angle measured. Some other total stations can also write these measurements to external data collector like a portable computer.

Total Station Functions
As is known by reading the working of total staion, the main functions performrd by this surveying instrument include coordinates determination, angle and distance measurement and data processing. However, these broad functions of total station can be divided into detailed funtions:

A total station with motor drive and scanning function at a given pitch of angles in horizontal and vertical direction. They can be manually operated for measuring single points or can be automatically tracked or driven with a motor drive.
Some of these instruments come with hand held digital camera to take stereo terrestrial photographs near the set total station. The camera is calibrated for subsequent procedures.
Many total stations can do image matching and 3D modeling. Such 3D measurement is accurate and stable in most cases.

Applications of Total Station
Total stations are mainly used in land surveying tasks. They are also used by archaeologists to record excavations and also by police, crime investigators, private accident reconstructionists and insurance companies to take measurements of scenes. Some of its area of application include:

Land Surveying
Mining
Road Mapping
Aerial photogrammetry
Calibration Labs/Test Houses

Tags:- Survey Total Station For Testing, Total Station Surveying Instrument

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