Total station – Principles and fundamentals

Total station is used for computing slant distances, horizontal and vertical angles, elevations in topographic and geodetic works, tacheometric surveys, etc. The total station is a pre-eminent contribution to modern surveying and hence the equipment is designed for speed, range, and accuracy. They are a combination of Theodolite and Electronic Distance measurement (EDM). This enables computing the vertical, horizontal as well as slope measurements.

They acts as a substitute for theodolite, EDM, Data collector, and a Microprocessor. Moreover, they are lightweight and compact machines and perform like transit stadia and plane table alidades.

The integration of microprocessors helps in the data collection and measurement computation process. Further to that, the inbuilt software helps to generate the maps instantly.

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Total station

Applications

Apart from taking the measurements, the total station helps in computing, interpreting, and documenting the data. Here is a list of activities that are computed, interpreted, and analyzed.

  • Horizontal angle
  • Vertical angle
  • Slope distance
  • Coordinate of point
  • Missing line measurement
  • Area calculation
  • Contour level

Principle of Total station

The total station consists of a built-in emitter, capable of emitting microwaves and infrared signals. The wavelength of these emitted waves helps in calculating the distance between the points.
Distance = velocity * time 

Here the distance is calculated by multiplying the time taken to cover a certain distance by the velocity. However, Triangulation and trigonometry methods are adopted for computing the angles and determining the coordinates.

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Major components

The Equipment is composed of different parts. Below listed are the major components.

Components of total station
Components
Components of total station
Components of total station
  • Handle
  • Handle securing screw
  • Data input/output terminal (Remove handle to view)
  • Instrument height mark
  • Battery cover
  • Operation panel
  • Tribrach clamp
  • Baseplate
  • Levelling foot screw
  • Circular level adjusting screws
  • Circular level
  • Display
  • Prism and prism pole
  • Objective lens
  • Tubular compass slot
  • The optical plummet focusing ring
  • Optical plummet reticle cover
  • Optical plummet eyepiece
  • Horizontal clamp
  • A horizontal fine motion screw
  • Data input/output connector
  • External power source connector
  • Plate level
  • Plate level adjusting screw
  • Vertical clamp
  • A vertical fine motion screw
  • Telescope eyepiece
  • Telescope focusing ring
  • Peep sight
  • Instrument centre mark

A tripod enables to affix the equipment onto the ground. A handle is available on the top of the equipment for holding it. There are a Data input and output terminal below the handle enabling the data transfer to the computer.
The total station comes with inbuilt software, an operation panel, keyboard, and a screen. The prism and prism poles helps in measuring distances.

Total station applications

The total station consists of an EDM, Theodolite, and a Microprocessor combined into one. They got a memory card for data storage and a battery. A fully charged battery works for about 3 to 5 hrs continuously.

  • Coordination determination
  • Distance measurement
  • Angular measurement
  • Data processing
  • Coordination Determination

The total station determines the coordinate of an unknown point. The instrument is placed over a known coordinate. The equipment digitally computes the coordinates.

Distance measurement

As mentioned earlier, the total station got an inbuilt miniature emitter. The emitters release the microwave signals. The prism reflector or object under survey at the other end reflects the waves. Onboard data interpreters compute the distance by emitting and receiving multiple frequencies.

Angular measurement

The total station uses the distance between the point and the time taken by the waves reflected for deciding angular measurement.

Data processing 

The integration of the microprocessor in a total station helps to read and interpret the survey parameters. Subsequently, the data stores in the memory card of the instrument and later transferred to a computer. They can compute multiple measurements with high precision with compensation for temperature, pressure, and humidity corrections.

Setting up of a total station

  • The basic steps involved in setting up are tripod setup, leveling, and instrument focusing.
  • The tripod legs are placed firmly on the ground with equidistant legs with the head position above the survey point.
  • The total station is placed on the tripod. It is fixed, and secured using a centering screw. 
  • The next step is to sharpen the optical plummet towards the survey point. On sharpening, the optical plummet reticle centers the survey point. 
  • The bubble is adjusted to the center by levelling foot screws
  • The time taken for leveling the equipment depend on the skill of the operator. However, leveling is the topmost activity to maintain the accuracy of measurements.
  • Adjust the plate level by loosening the horizontal clamp. The equipment is parallel to levelling foot screw.
  • Turn the instrument at 90 degree and leveled using 3rd leveling screw.
  • Subsequently, turn on the instrument.
  • Select the tilt function from the opening window followed by adjusting the foot level screw and center the bubble.
  • Rotate the instrument at 90 degree. Repeat the process.
  • Finally, adjust the ring and focus the telescope to the target point.
Total station prism
Total station prism

Advantages of Total station

There are a lot of advantages of total station as follows.

  • High precision and accuracy.
  • Requires limited manpower 
  • Perform quick field work
  • Reduction in manual errors.
  • Correction for temperature, pressure etc and digitally rectified. 
  • Storage and interpretation of data is easy
  • Time consumed is less.
  • Inbuilt GIS software helps in instant map creation
  • Assists in local languages.

Disadvantages of Total station

  • The cost of the instrument is high.
  • Need high skilled surveyor with AutoCAD knowledge and professional training.
  • Checking errors during the operation is impossible.
  • Low battery life.

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