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SURVEYING & INSTRUMENT

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    Introduction

    One of the most fundamental surveying

    operations is the measurement of

    horizontal distance between two points on

    the surface of the earth

    !here are two basic methods used"

    Direct

    Indirect

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    Introduction

    Direct linear measurements are methods

    used for determining horizontal distances

    with a tape #or chain$ and%or with an

    electronic distance measuring instrument

    In indirect methods the transit and

    stadia or theodolite and stadia are used

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    'orizontal Distance

    (

    )

    '()

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    *ertical Distance

    (

    )

    *()

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    Slope Distance

    )

    S()(

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    +ubits

    Distance is one of the most basic

    engineering measurements

    ,arly measurements were made in terms

    of the dimensions of the body

    Cubits - the distance between the tip of

    your middle finger to the elbow

    !ypically to measure cords and te.tiles

    #another measure was /0 digits or 1 palms$

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    2athom

    Fathom - distance between the tips of

    your middle finger when your arms are

    outstretched

    !he name comes from the Danish faedn

    3outstretched arms3

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    2oot

    Foot distance from the tip of a man4s big

    toe to the heel

    Rod - the sum of the lengths of the left

    feet of 51 men #516 - /0 ft$

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    (pproaches

    (pproaches in measuring horizontaldistance 7acing

    Optical rangefinders Odometers

    !achometry

    !aping or +haining ,lectronic Distance Measurement #,DM$

    8lobal 7ositioning System #87S$

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    7acing

    ( person can determine their pace by

    counting the number of paces necessary

    to wal9 a distance that has been

    previously measured

    ( pace is defined as one step

    ( stride is consider two steps

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    +haining

    !he most common method used in

    determining or laying off linear

    measurements for construction surveys

    triangulation base lines and traversedistances is often referred to as chaining

    2or centuries engineers have measured

    distances with ropes lines or cords

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    +haining

    !he term chaining is a carry:over from

    the time when the 8unter chain was used

    #51;;4s-5

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    8unter +hain

    !he surveyor@s chain was called 8unter@s after its inventor

    the ,nglish mathematician and astronomer ,dmund 8unter

    #56>5-51/1$

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    !aping

    (ccuratesurveyors@tapes made of

    steel or a steelalloy with atypical lengthof 5;; feet or

    5;; meterswere used forsurveying

    distances

    5>=;4s surveyor4s steel tape

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    !aping

    2or very accurate measurements the

    temperature of the tape must be ta9en into

    account as well as the tension of the pull

    ,ach Steel !ape had its own temperature

    and tension coefficient which was used to

    correct each measurement

    Aon-metallic tapes are now common

    that are woven from synthetic yarns

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    (ccuracy

    Pacing; 5%6; to 5%/;;B Ceconnaissance

    Odometer; 5%/;;B Ceconnaissance

    Taping; 5%5;;; to 5%6;;;B and surveys EDM; E;;0 to 5%F;;;;;B (ll types of

    surveying

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    Duties of

    +haining%!aping Members

    !he smallest chaining group could consist

    of only two people one at each end of the

    tape

    !he person ahead holding the zero end

    is called the head chainman #bac9 man$

    !he other person is 9nown as the rear

    chainman #front man$

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    7lumb-bob and 7eg

    ( plumb-bob is used to locate the

    measurement point on the tape vertically

    above a fi.ed mar9er or to place taping

    pins to mar9 tape lengths

    ,ach end point of a measurement is

    mar9ed by placing the plumb-bob string

    over the tape

    7egs is set out to mar9 the positions

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    7eg

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    Site SetupStraight ine

    ( straight line isthe shortest

    distance between

    two points on a

    map or between

    two points on the

    field

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    Site Setup7lacing Canging 7ole

    !he correct way to hold a

    ranging pole is to 9eep it

    loosely between thumb

    and inde. finger about 5;

    cm above the soil

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    Site Setupong Distance Straight ine

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    Site Setupong Distance Straight ine

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    Site Setupong Distance Straight ine

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    Site SetupOver ( Cidge or ( 'ill

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    Site SetupOver ( Cidge or ( 'ill

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    Site SetupOver ( Cidge or ( 'ill

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    Site SetupOver ( Cidge or ( 'ill

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    Site SetupOver ( Cidge or ( 'ill

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    Measuring DistanceShort Distance

    Tip

    ,ach small division

    represents 5mm So if

    the nail is positioned two

    small divisions after=/>; mm it is mar9ing

    =/>/ mm

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    Measuring Distanceong Distance

    !he head chainman also acts as the

    recorder also reads and records the

    temperature of the tape

    !he rear chainman is responsible for

    9eeping the tape in alignment

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    Measuring Distanceong Distance

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    Stretcherman

    2or more precise taping a three-man

    party is essential

    In addition to the head and rear chainmen

    a stretchermanis added

    !he duties of the stretchermanare to

    apply and to maintain the correct tension

    on the tape while the chainmen do the

    measuring

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    Measuring Distancein ( !all 8rowing +rop

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    !aping over evel 8round

    If the taping is done over level ground

    where there is no underbrush the tape

    can rest on the ground

    if the distance being measured is greater

    than a tape length it is necessary to mar9

    the terminal point with a range pole

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    )rea9ing !ape

    !he term brea9ing tape is used to

    describe the procedure for measuring

    directly horizontal distance on sloping

    ground or through obstacles that do notpermit the use of a full tape length

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    Measuring Distancein Steep Sloping (reas

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    Measuring Distancein Steep Sloping (reas

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    !aping around Obstacles #5$

    Ghere an obstruction #eg boulder tree

    etc$ lies on the measurement line it will

    be necessary to brea9 the tape around the

    obstacle

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    !aping around Obstacles #/$

    'orizontal angles and are used totransform the resulting horizontal lengths

    to an eHuivalent horizontal length alongthe measurement line

    5 /

    F

    0 6

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    !aping around Obstacles #F$

    'orizontal angles are measured using a

    compass or are calculated using the

    cosine law

    (

    )+

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    Ceview )asic !rigonometry

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    Ma9ing !ape +orrections #5$

    Off all the measurement method taping is

    probably the least automated and most

    susceptible to personal and natural errors

    !he basic error arise due to

    defect in the tape

    natural error due to weather conditions

    human errors resulting in tape reading errors

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    Ma9ing !ape +orrections #/$

    ( tape supported only at the ends has a

    sag in it

    Ghen it indicates 5;;;; m actually the

    distance measured is less

    ( steel tape will be longer when it is

    warm than when it is cold

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    Ma9ing !ape +orrections #F$

    (ll tapes are graduated under controlled

    conditions of temperature and tension

    Ghen they are ta9en to the field these

    conditions change

    !he tape regardless of the material used

    to ma9e it will be either too short or too

    long

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    Ma9ing !ape +orrections #F$

    2or low accuracy surveys the amount oferror is too small to be considered

    (s accuracy reHuirements increase

    variations caused by the temperature andsag must be computed and used to correctthe measured distance

    !ape corrections are typically relativelysmall #ie 5J of the measured distance$but still significantK

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    Standardisation #5$

    !aping cannot be more accurate that the

    accuracy to which the tape is

    standardised

    !he tape should be standardised by

    appropriate authority

    !he tape will be return with certificate on

    true length and standard condition oftemperature and tension

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    Standardisation #/$

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    Incorrect !ape 8raduation #5$

    actual measurement distance may be

    shorter #ll4$ or longer #lLl4$ than measured

    due to errors in tape graduation

    !he correction is assumed proportional to

    the tape length and can be applied to the

    total measured length

    +orrection factor +

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    Incorrect !ape 8raduation #/$

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    !hermal ,.pansion #5$

    !apes have been standardised#calibrated$ to a specific temperature

    (ctual measurement distance may be

    shorter #!!o$ or longer #!L!o$ thanmeasured due to thermal e.pansion of thetape

    +orrection uses the air temperature duringtaping and may be applied to the totalmeasured length

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    !hermal ,.pansion #/$

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    7ull%!ension #5$

    !apes have been standardised to aspecific tension%pull

    (ctual measurement distance may be

    shorter #77o$ or longer #7L7o$ thanmeasured depending on the amount oftension applied to the tape

    +orrection uses the tension applied duringtaping and may be applied to the totalmeasured length

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    7ull%!ension #/$

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    Sag #5$

    !he actual measurement distance may be

    shorter than the measured length due to sagging

    of the tape because of its weight or the wind

    Sagging is a function of the pull%tension appliedto the tape and the support conditions

    !ypically the tape is supported at the ends only

    but may also be supported throughout or at

    midpoints

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    Sag #/$

    +orrection is applied to each individual

    unsupported length and the total sag

    correction #+S!$ is the sum of the sag

    corrections for each unsupported tapelength used to ma9e up the measurement

    line

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    Sag #F$

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    Specifications

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    Slope #5$

    Sloping tape with levelling actual

    measurement distance is shorter than the

    measured tape length

    ,levation change across the measurementlength is used to correct measured length

    to actual distance

    ,levation change is measured usinglevelling

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    Slope #/$

    +orrection factor +

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