MEASUREMENT OF DISTANCE There are two main methods of determining distance

Direct Method distances are actually measured onground by means of a chain, tape or other instruments.

Computative Method distances are obtained bycalculations as in tacheometry, telemetry or triangulation.

DIRECT MEASUREMENT(METHODS)

Several methods are available, Pacing Passometer Pedometer Odometer Speedometer Perambulator Judging distance Time measurement Chaining

Contd PACING Where approximate result is required, distance may be determined by

pacing. This method is used for reconnaissance survey, for preparation of military

plans etc. Also used for approximate checking of distance. The method consists of walking over a line and

counting the number of paces and than therequired distance may be obtained by multiplyingthe number of paces by the average length ofpace.

The length of pace varies with the: Individual, age, height and physical condition The nature of the ground (uphill and

downhill) The slope of the country and The speed of pacing

PASSOMETER: Passometer is a pocket instrumentwhich count the number of paces. It automatically records the numberof paces. Its mechanism is being operated by themotion of the body. It should be held vertically in pocket.

PEDOMETER: The device which measured the distanceautomatically is known as pedometer. It is similar to Passometer but differenceis that Passometer count the number ofpaces whereas pedometer records thedistance. It is adjusted according to the length ofthe pace of the person carrying it.

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ODOMETER: It measures the distance approximately. It can be attached to the wheel of anyvehicle, such as carriage, cart bicycle, etc. It registers the number of revaluation of thewheel. Knowing the circumference of the wheel,the distance traversed may be obtained bymultiplying the number of revolutions by thecircumference of the wheel.

PERAMBULATOR: It can measure distance rapidly. It consist a single wheel provide with forksand a handle. It is wheeled along the line, the length ofwhich is desire. The distance traversed is automaticallyregistered on the dial or an odometerattached. The reading approximates an rough ground.

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SPEEDOMETER: The Speedometer of an automobilemay be used to measure distancesapproximately. It gives better results than pacing,provided the route is smooth.

JUDGING DISTANCE: This is very rough method ofdetermining distance. It is used reconnaissance survey.

TIME MEASUREMENT: Distance is roughly determined bytime intervals of travel. Knowing the average time per km fora person at walk or a horse, thedistance traversed may be easilyobtained.

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ELECTRONIC DISTANCE MEASURING TOOL

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CHAINING Measuring distance with chain or tape is themost accurate and common method.

For work of ordinary precision a chain is used. Where great accuracy is required, a steel tapeis used.

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LENGTH MEASURING TOOLSChain

Metric chainGunters ChainRevenue ChainEngineers chain

TapesCloth or linen Tape

Metric Woven Metallic TapeMetric steel Tape

Invar tape.Synthetic Tape.

OTHER ACCESSORIES Arrows (chain pins) Wooden Pegs Ranging Rods. Ranging Poles.

Offset Rod. Laths & Whites Plumb Bob Abneys Level

CHAIN The chain is composed of 100 or 150 pieces of galvanized mild

steel wire 4mm in diameter called links. The end of each link are bent into a loop and connected

together by means of three oval rings. The ends of the chain are provided with brass handles for

dragging the chain on the ground. The length of link is the distance between the centers of the

two consecutive middle rings. The end links includes the handles. Metallic tags or indicators are fixed at various distinctive of

the chain to facilitate quick reading.

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METRIC SURVEYING CHAINS: The chains are made in lengths of 20 and 30 meters. To enable reading a chain, tallies (tags) are fixed at every five meter

length and small brass rings are provided at every meter length. To facilitate holding of the arrows in position with the handle, a

groove is cut on the outside surface of the handle. The handle joints are flexible. The tallies used for marking the distances in a metric chain are

marked with letters Me and m.

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STEEL BAND The steel, band, also called the band chain, consists of a tape

of steel with a brass swivel handle at each end. It is 20m or 30 m long and 16 mm wide. It is wound on an open steel cross or on a metal reel in a

closed case. The graduations are marked in two ways :

The band is divided by brass studs at every 0.2 m and numbered atevery 1 m the first and the last link being subdivided into cm and mm.

The graduations are etched as meters, decimeters, centimeters on oneside and 0.2 m links on the other.

Brass tallies are fixed at every 5 m length of the band.

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Steal Band Chain

P R O S & C O N S(STEEL BAND VS CHAIN)

It is best adapted to general field work and rough usage. For accurate work the steel band is now preferred. It is lighter and easier to handle than the chain. It is practically unchangeable in length. However, if sufficient care is not taken it is easily broken. It cannot be repaired in the field, as it is repaired only by soldering,riveting or by clipping, while the chain can easily be repaired. It must be protected from rust by frequent cleaning and oiling. It cannot be read so easily as the chain. On the other hand, the chain is not only heavy and cumbersome, but alsoit has many wearing surfaces and, therefore, it is too much liable toincrease in length by stretching when in continued use. It also gets shortened due to bending of the links and mud adhering to thelinks. Being heavier, the chain sags considerably when suspended. But chains also known to be suitable for rough usage, and they could alsobe read easily.

Gunters Chain: It is 66 fit long and is divided into 100 links. Each link is 0.66 ft long. It is very convenient for measuring distance in miles andfurlongs. Also for measuring area when the units of area is an acre.

Revenue Chain: It is commonly used for measuring fields in cadastral survey. It is 33 ft long and divided into 16 links. Each link is 2.0625 ft long.

Engineers chain: It is 100 ft long and it is divided into 100 links. Each link is 1 ft in a length. Used in all Engineering surveys.

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