Linear Methods of Surveying | Introduction to Surveying | By Ashutosh Nautiyal

Linear Methods of Surveying 

It can be classified into three types:- 

• Direct method

 

• Electronic method

• Optical method 

Linear Methods of Surveying

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