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__Linear Methods of Surveying __

## It can be classified into three types:-

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- Direct method

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- Electronic method

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- Optical method

## Direct method:-

The direct method is further divided into five types:-

## Pacing:-

- The pacing technique is mostly employed in preliminary surveys and explorations.

- In this method, the surveyor is required to conduct a rough survey quickly.

- It also roughly checks the distance measured by other means.

- The number of paces between the two points of the line is counted.

- Knowing the average length of the pace helps to know the length of the line.

- The length of the pace is dependent on the person who is measuring, the ground, the speed of pacing and the slope of the country.

- By walking on an approximate level ground over various lines of known lengths helps in determining the length of one's natural step.

- It is a difficult process to perform pacing over a rough surface or on slopes.

## Passometer:-

- The passometer is a watch-like instrument that is carried on the person's pocket or tied on the man's leg.

- This instrument records the paces when the man moves from one point to another.

- The distance is calculated by multiplying the number of paces by the average length of the pace.

- This method overcomes the monotony and strain in counting the paces by the surveyor.

## Pedometer:-

- The pedometer is a device similar to passometer but it is adjusted to the length of the pace of the person carrying it.

- It registers the total distance covered by any number of paces.

- It automatically measures the distance.

- It is best in measuring vertical distances.

## Odometer:-

- The odometer is an instrument that measures the number of revolutions of a wheel.

- It is fitted to the wheel that is rolled along the line whose length is required.

- The distance covered is calculated by multiplying the number of revolutions taken to cover the length by the circumference of the wheel.

- This instrument does not provide accurate results on an undulating surface.

- When the surface is smooth, the speedometer used in vehicles can be used.

## Chaining:-

- In Chaining method, the distance is determined by means of a tape or a chain.

- This is one of the accurate methods to determine the linear measurements.

- The chain is used for ordinary precision.

- Tape or a special bar is used to measure distance with high precision.

- The distances determined by chaining form the basis of all surveying.

- It is the accurate and commonly employed method in surveying.

- No matter how accurately the angles may be measured, the survey can be no more precise than the chaining.

- The instruments used for determination of the length of a line by chaining are chain or tape, arrows, pegs, ranging rods, offset rods and plumb bob.

- Depending upon the material used, the tapes are classified as cloth or linen tape, metallic tape, steel tape and invar tape.

## Electronic method:-

- Electronic equipment used for measuring distances is called an electronic distance measurement (EDM) instrument.

- They rely on the measurement of electromagnetic waves and measuring even fraction of wavelength by phase difference technique.

- Distances are measured with instruments that rely on propagation, reflection and subsequent reception of either radio or light waves.

- The various instruments that are used under the electronic methods are Geodimeter, Tellurometer, the Decca navigator and the Lambda Position Fixing System.

- The method of measurement in the case of Geodimeter is assessed on the propagation of modulated light waves.

- The other three instruments use radio waves for distance measurements.

- These instruments even display the distance measured.

- They are costly and delicate.

- For ordinary surveying, they are not used commonly.

## Optical method:-

- In this method, observations are taken through a telescope and distances are determined by calculation such as in tachometer or triangulation.

- The tachometer (stadia is the common term in the USA) is a surveying method utilized to quickly determine the horizontal distance to, and elevation of, a point.

- Stadia observations are accessed by sighting through a telescope equipped with two or more horizontal cross wires in a spacing that is known.

- The apparent intercepted length between the bottom and top wires is read onto a graduated rod held vertically in the desired stage.

- The space from the telescope to a rod is seen by proportional relationships in similar triangles.

*Self Typed

*Source- Internet, Books, Self-Analysis