Introduction to Total Station
In surveying, the advanced electronic instrument used to measure horizontal and vertical angles along with distance is called total station.
In field Survey, based instruments is now so widespread that it would be difficult to imagine any contemporary site surveying without it.
The recent applications of electronics in the surveying instruments has enabled the surveyors to collect and process the field data much more easily and to a higher precision than is possible using routine instruments.
Electronic theodolite is combined and interfaced with EDMs and electronic data collectors, they become total stations or electronic tacheometers ET.
These total stations can read and record horizontal and vertical angles, together with slope distances.
These are operated using a mulfi-function keyboard which is connected to a microprocessor built into the instrument.
The microprocessor in the total station cannot only perform a variety of mathematical operations, but in some cases can also store observations directly using an internal memory.
Features of Total Station
(a) Angle Measurement :
An electronic theodolite of a total station is used to measure angles. All the features of electronic theodolites are same as total station.
A total station can record angles with a resolution between 1″ and 20″. All the instruments incorporate either single-axis or dual-axis compensator, the latter being expensive.
(b) Distance Measurement :
Generally a total station measures a slope distance and the microprocessor uses the vertical angle recorded by the theodolite along the line of sight to calculate the horizontal distance.
In addition, the height between the trunion axis and prism center is also calculated and displayed.
All the total stations use co-axial optics in which the EDM transmitter and receiver are combined with the theodolite telescope.
These 3 modes are generally available for distance measurement.
#Standard or Coarse Mode
It has a resolution of 1 mm and measurement time of 1-2 seconds.
#Precise or Fine Mode
It has a resolution of 1″ but a measurement time of 8 – 4 seconds. This is more accurate than the standard mode, since the instrument refines the arithmetic mean value by making repeated measurements.
#Tracking or Fast Mode
The distance measurement is repeated automatically at interval of less than 1″. Normally this mode has a resolution of 10 mm.
(c) Control Panel :
The total station is activated through its control panel. It consists of keyboard and multiple line liquid crystal display (LCD).
The LCD is moisture-proof, can be illuminated and some LCD’s incorporate contrast controls to accommodate different viewing angles.
Some of the total stations have two control panels, one of each face the electronic theodolite to make them easier to use.
The keyboard enables the user to select different measurement and implement modes, enables instrument parameters to be changed and allows special software functions to be used.
Angle and distances are usually recorded electronically in a digital form as data. If a code is entered from the keyboard to define the feature being observed the data can be processed much more quickly by downloading it into appropriate software.
On numeric keyboards, codes are represented by numbers, whereas keyboards with feature codes are also available.
(d) Power Supply:
Rechargeable nickel- cadmium batteries are used for power supply. The usage time is 2-10 h.
Some total stations have an auto power save feature which switches the instrument off or into some standby mode after it has not been used for a specified time.
Capabilities of a Total Station
- Monitors : battery status, signal attenuation, horizontal and vertical axes status, collimation factors.
- Computes coordinates.
- Traverse closure and adjustment.
- Topography reductions.
- Remote object elevation.
- Distance between remote points.
- Inversing.
- Resection.
- Horizontal and vertical collimation.
- corrections.
- Setting out.
- Vertical circle indexing.
- Record, search and review.
- ‘On-board software.
- Transfer of data to the computer
- Transfer of computer files to the data recorder.
Advantages of Total station
- Quick collection of information.
- Multiple surveys can be performed at one set up location.
- Easy to perform distance & horizontal measurements.
- Layout of construction site quickly and efficiently.
- Digital design data from CAD programs can be uploaded to data collector.
- Daily survey information can also be quirky downloaded into CAD. Which eliminates data manipulation time required using conventional survey techniques.
Disadvantages of Total station
- Elevation of a point may not be accurate as with levelling instrument.
- Horizontal co-ordinates are calculated on a rectangular grid system. But actually if should be on spheroid and rectangular co-ordinates & must be transformed to geographic co-ordinates.
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Also Read : What is Geographic Information System (GIS) ?
Also Read : Global Positioning System { GPS } in Surveying