SURVEYINGSURVEYINGPreamblePreamble

Surveying is involved in a project from conceptual Surveying is involved in a project from conceptual stage to construction and afterwards in stage to construction and afterwards in maintenance also. Depending on the stage at which maintenance also. Depending on the stage at which surveying is carried out it can be called.surveying is carried out it can be called.

i)i) Pre construction Pre construction surveysurvey

Feasibility survey (RECT, PECT)Feasibility survey (RECT, PECT)

ii)ii) Construction Construction surveysurvey

To maintain alignment and To maintain alignment and Geometry control during Geometry control during construction. (FLS and other )construction. (FLS and other )

iii)iii) Post Post constructionconstruction

Maintenance surveyMaintenance survey

Definition : Definition : Operation of making such Operation of making such measurements that the relative position of measurements that the relative position of various features, natural or Artificial on the various features, natural or Artificial on the surface of the earth can be exhibited in their surface of the earth can be exhibited in their correct Horizontal and vertical relationship.correct Horizontal and vertical relationship.

Normally determining position in Horizontal Normally determining position in Horizontal plane is called surveying.plane is called surveying.

Determining relative heights or depth is called Determining relative heights or depth is called levelling.levelling.

PurposePurpose : : The main object of surveying is the The main object of surveying is the preparation of maps or plans which are the basis in preparation of maps or plans which are the basis in planning and design of engineering project such as planning and design of engineering project such as route location of railway line, roads and water supply route location of railway line, roads and water supply scheme.scheme.

Basic Principles in SurveyingBasic Principles in Surveying : : Ruling Ruling principle of survey is :principle of survey is :i) “ to work from whole to part”. For surveying i) “ to work from whole to part”. For surveying Establish control points with high precision by use of Establish control points with high precision by use of Triangulation and precise levelling. Area is further Triangulation and precise levelling. Area is further divided into triangle, which are surveyed with less divided into triangle, which are surveyed with less accuracy.accuracy.ii) to fix the position of new stations by atleast two ii) to fix the position of new stations by atleast two independent processes – By linear and Angularindependent processes – By linear and Angular

Classification of SurveysClassification of Surveys : : Surveying is divided into Surveying is divided into two main categories-two main categories-i) Geodetic Surveyi) Geodetic Surveyii) Plane surveyii) Plane survey

i) Geodetic Survey :-i) Geodetic Survey :- When survey extends over a When survey extends over a large areas more than 200 sq. km. and degree of large areas more than 200 sq. km. and degree of accuracy is also great. The curvature of earth is also accuracy is also great. The curvature of earth is also taken into account. Geodetic survey is used to provide taken into account. Geodetic survey is used to provide control points to which small surveys can be connected.control points to which small surveys can be connected.

ii) Plane Survey :-ii) Plane Survey :- For small projects covering Area For small projects covering Area less than 200 sq.km. Earth curvature is not counted for less than 200 sq.km. Earth curvature is not counted for in distances. Earth surface is considered as plane. in distances. Earth surface is considered as plane. (Angular error of 1” in 200 sq. km. area by assuming (Angular error of 1” in 200 sq. km. area by assuming plane).plane).

A)A) Classification based upon equipment usedClassification based upon equipment used::

i) Chain surveyi) Chain surveyii) Compass surveyii) Compass surveyiii) Theodolite surveyiii) Theodolite surveyiv) Plane Table surveyiv) Plane Table surveyv) Tachometric surveyv) Tachometric surveyvi) Aerial Photographic Surveyvi) Aerial Photographic Surveyvi) Remote sensing.vi) Remote sensing.

B) Based upon Method Employed :B) Based upon Method Employed :i) Triangulation :i) Triangulation : Control points are established Control points are established through a net-work of triangles.through a net-work of triangles.

ii) Traversing:ii) Traversing: Scheme of control points Scheme of control points consisting of a series of connected lines.consisting of a series of connected lines.

iii) Trilateration:iii) Trilateration: Distances are measured for Distances are measured for exercising the control.exercising the control.

Levelling :Levelling :The art of determining relative altitudes The art of determining relative altitudes of points on the surface of the earth of of points on the surface of the earth of beneath the surface of earth is called beneath the surface of earth is called LEVELLING.LEVELLING.

For execution of Engineering Projects it is For execution of Engineering Projects it is very necessary to determine elevations of very necessary to determine elevations of different points along the alignment of different points along the alignment of proposed project.proposed project.

Other applications are :Other applications are :i) Taking rail levels existing before track renewals to i) Taking rail levels existing before track renewals to finalise final rail level profile including vertical curves.finalise final rail level profile including vertical curves.ii) Initial ground levels for earthwork calculations.ii) Initial ground levels for earthwork calculations.iii) Levels for measurement of earthwork.iii) Levels for measurement of earthwork.iv) Measurement of ballast etc.iv) Measurement of ballast etc.

Terms used in Levelling –Terms used in Levelling –a) DATUM – a) DATUM – or Datum plane is an arbitrarily assumed or Datum plane is an arbitrarily assumed level surface or line with reference to which level of level surface or line with reference to which level of other line or surface are calculated.other line or surface are calculated.

b) REDUCED LEVEL (RL) –b) REDUCED LEVEL (RL) – Height or depth of a Height or depth of a point above or below the assumed datum is called point above or below the assumed datum is called Reduced level.Reduced level.c) BENCH MARK –c) BENCH MARK – (BM) – (BM) – B.M. is a fixed reference B.M. is a fixed reference point of known elevation. It may be of the following point of known elevation. It may be of the following types.types.i) GTS Bench mark (i) GTS Bench mark (Geodetic Triangulation Survey) :Geodetic Triangulation Survey) :

These Bench marks are established by national These Bench marks are established by national agency like Survey of India. They are established agency like Survey of India. They are established with highest precision. Their position and elevation with highest precision. Their position and elevation above MSL is given in a special catalogue known as above MSL is given in a special catalogue known as GTS Maps ( 100 km. interval).GTS Maps ( 100 km. interval).

ii) ii) Permanent Bench Mark :Permanent Bench Mark : They are fixed They are fixed points of reference establish with reference to GTS points of reference establish with reference to GTS Bench mark (10 km. interval).Bench mark (10 km. interval).

iii) Arbitrary Bench mark :iii) Arbitrary Bench mark : These are These are reference points whose elevations are arbitrarily reference points whose elevations are arbitrarily assumed. In most of Engineering projects, the assumed. In most of Engineering projects, the difference in elevation is more important than their difference in elevation is more important than their reduced levels with reference to MSL as given in a reduced levels with reference to MSL as given in a special catalogue known as GTS Maps ( 100 Km. special catalogue known as GTS Maps ( 100 Km. interval).interval).

d)d)Mean Sea Level (M.S.L.) :Mean Sea Level (M.S.L.) : M.S.L. is obtained by M.S.L. is obtained by making hourly observations of the tides at any place making hourly observations of the tides at any place over a period of 19 years. MSL adopted by Survey of over a period of 19 years. MSL adopted by Survey of India is now Bombay which was Karachi earlier.India is now Bombay which was Karachi earlier.

e) Level Surface :e) Level Surface : The surface which is parallel to The surface which is parallel to the mean sphereoidal surface of the earth is known as the mean sphereoidal surface of the earth is known as level surface.level surface.

ff) Line of Collimation :) Line of Collimation : It is the line joining the It is the line joining the intersection of the cross hair and the optical center of intersection of the cross hair and the optical center of the objective and its extensions, it is also called line of the objective and its extensions, it is also called line of sight or collimation.sight or collimation.

g)g) Height of Instrument (HI) :Height of Instrument (HI) : The elevation of the line The elevation of the line of sight with respect to assumed datum is known as of sight with respect to assumed datum is known as HI.HI.

h) Back sight : (B.S.) -h) Back sight : (B.S.) - The first sight taken on a The first sight taken on a levelling staff held at a point of known elevation. B.S. levelling staff held at a point of known elevation. B.S. enables the surveyor to obtain HI +sight i.e. Height of enables the surveyor to obtain HI +sight i.e. Height of Instrument or line of sight.Instrument or line of sight.i) Fore Sight : (F.S.) –i) Fore Sight : (F.S.) – It is the last staff reading taken It is the last staff reading taken from a setting of the level. It is also termed as minus from a setting of the level. It is also termed as minus sight.sight.Fore sight is the sight taken on a levelling staff held at Fore sight is the sight taken on a levelling staff held at a point of unknown elevation to ascertain the amount a point of unknown elevation to ascertain the amount by which the point is above or below the line of sight. by which the point is above or below the line of sight. This is also called minus sight as the foresight reading This is also called minus sight as the foresight reading is always subtracted from height of Instrument.is always subtracted from height of Instrument.

k) Change Point (CP) :k) Change Point (CP) : The point on which The point on which both the foresight and back sight are taken both the foresight and back sight are taken during the operation of levelling is called during the operation of levelling is called change point.change point.

l) Intermediate Sight (IS) :l) Intermediate Sight (IS) :The foresight taken on a levelling staff held The foresight taken on a levelling staff held at a point between two turning points, to at a point between two turning points, to determine the elevation of that point, is determine the elevation of that point, is known as intermediate sight.known as intermediate sight.

It may be noted that for one setting of a level, there It may be noted that for one setting of a level, there will be only one back sight and one foresight but will be only one back sight and one foresight but there can be any number of intermediate sights.there can be any number of intermediate sights.

Type of Levelling Equipments:Type of Levelling Equipments:i) i) Dumpy levelDumpy levelii) Tilting levelii) Tilting leveliii) Automatic leveliii) Automatic leveliv) Digital Auto leveliv) Digital Auto level

Dumpy level :Dumpy level : It is simple compact and stable. The It is simple compact and stable. The telescope is rigidly fixed to its support therefore telescope is rigidly fixed to its support therefore cannot be rotated about its longitudinal axis. A long cannot be rotated about its longitudinal axis. A long bubble tube is attached to the top of telescope. bubble tube is attached to the top of telescope. Dumpy literally means short and thick.Dumpy literally means short and thick.

Tilting level :Tilting level : It consists of a telescope It consists of a telescope attached with a level tube which can be tilted attached with a level tube which can be tilted within few degrees in vertical plane by a tilting within few degrees in vertical plane by a tilting screw.screw.

The main peculiarity of this level is that the The main peculiarity of this level is that the vertical axis need not be truly vertical, since the vertical axis need not be truly vertical, since the line of collimation is not perpendicular to it. The line of collimation is not perpendicular to it. The line of collimation, is, however, made horizontal line of collimation, is, however, made horizontal for each pointing of telescope by means of tilting for each pointing of telescope by means of tilting screw. It is mainly designed for precise levelling screw. It is mainly designed for precise levelling work.work.

The Automatic level : The Automatic level : Also termed as self Also termed as self aligning level. The fundamental aligning level. The fundamental difference between automatic and the difference between automatic and the classic spirit level is that in the former classic spirit level is that in the former the line of sight is no longer levelled the line of sight is no longer levelled manually using a tubular spirit level, but manually using a tubular spirit level, but is levelled automatically within a certain is levelled automatically within a certain tilt range. This is achieved by tilt range. This is achieved by compensator in the telescope.compensator in the telescope.

Advantage of automatic levelAdvantage of automatic leveli)i) Much simpler to use Much simpler to useii) ii) High precisionHigh precision – Mean elevation error – Mean elevation error on staff graduated to 5mm division varies on staff graduated to 5mm division varies between +0.5 to 0.8 mm per km of forward between +0.5 to 0.8 mm per km of forward and backward levelling.and backward levelling.iii) iii) High speedHigh speed : For fly levelling the : For fly levelling the progress achieved by various level-wise progress achieved by various level-wise compared.compared.

Type of level D(m) 20m 40 60 80 100 120Type of level D(m) 20m 40 60 80 100 120Automatic level speed 1.2 2 2.4 2.5 2.6 2.7Automatic level speed 1.2 2 2.4 2.5 2.6 2.7 S(Km/hr) S(Km/hr)Tilting level speed 0.6 1.1 1.5 1.7 1.8 1.9Tilting level speed 0.6 1.1 1.5 1.7 1.8 1.9 S(Km/hr) S(Km/hr)

S = Speed of levelling in km/hr.S = Speed of levelling in km/hr.D = Sighting distance in meter.D = Sighting distance in meter.The speed of Dumpy level is about 25% lower than The speed of Dumpy level is about 25% lower than tilting level.tilting level.iv)iv) Freedom from errorsFreedom from errors – Accuracy is increased by – Accuracy is increased by an errect telescope image.an errect telescope image.v) Range of applicationv) Range of application – level can be used on – level can be used on medium and large sized projects and setting bench medium and large sized projects and setting bench marks.marks.

Basic components of level :Basic components of level :1. Telescope1. Telescope – to provide a line of sight – to provide a line of sight

2. Level Tube2. Level Tube – to make line of sight horizontal – to make line of sight horizontal

3. Levelling head3. Levelling head – to bring the bubble of tube level – to bring the bubble of tube level at the centre of its run.at the centre of its run.4. Tripod4. Tripod – to support the above three parts of the – to support the above three parts of the level.level.1. TELESCOPE1. TELESCOPE : : Telescope is an optical Telescope is an optical instrument used for magnifying and viewing the instrument used for magnifying and viewing the images of distant objects. It consists of two lenses. images of distant objects. It consists of two lenses. The lens fitted near the eye is called the eye piece and The lens fitted near the eye is called the eye piece and the other fitted at the end near to the object is called the other fitted at the end near to the object is called the objective lens.the objective lens.

The objective provides a real inverted image The objective provides a real inverted image infront of the eye piece at a distance lesser than infront of the eye piece at a distance lesser than its focal distance.its focal distance.Two essential conditions are involved. : Two essential conditions are involved. : i) The real image of the object, must be formed.i) The real image of the object, must be formed.Ii) the plane of image must coincide with that of Ii) the plane of image must coincide with that of cross hairs.cross hairs.Focusing of Telescope : Focusing of Telescope : The operation of The operation of obtaining a clear image of the object in the plane obtaining a clear image of the object in the plane of cross hairs is known as focusing.of cross hairs is known as focusing.

1. Diaphram :1. Diaphram : A frame carrying cross hairs usually A frame carrying cross hairs usually made of either silk thread or platinum wire and placed at made of either silk thread or platinum wire and placed at the plane at which vertical image of the object is formed the plane at which vertical image of the object is formed by the objective.by the objective. Vertical hair of the diaphram enables the surveyor to Vertical hair of the diaphram enables the surveyor to check the verticality of levelling staff whereas horizontal check the verticality of levelling staff whereas horizontal hairs are used to read the staff graduations.hairs are used to read the staff graduations.

2.Level Tube :2.Level Tube : Also known as Bubble Tube consists of Also known as Bubble Tube consists of a glass tube placed in a brass tube which is sealed with a glass tube placed in a brass tube which is sealed with plaster of paris. The whole of the interior surface or the plaster of paris. The whole of the interior surface or the upper half is accurately ground so that its longitudinal upper half is accurately ground so that its longitudinal section, is an arc of a circle. Level tube is filled with section, is an arc of a circle. Level tube is filled with either or alcohol, the remaining space is occupied by an either or alcohol, the remaining space is occupied by an air bubble. The centre of air bubble always rest at the air bubble. The centre of air bubble always rest at the highest point of the tube.highest point of the tube.

Outer surface of the bubble tube is graduated Outer surface of the bubble tube is graduated in both the directions from the centre.in both the directions from the centre.

The line tangential to the circular are at its The line tangential to the circular are at its highest point i.e. the middle of tube is called highest point i.e. the middle of tube is called the axis of bubble tube. When the bubble is the axis of bubble tube. When the bubble is central the axis of bubble becomes Horizontal.central the axis of bubble becomes Horizontal.

The level tube is attached on the top of The level tube is attached on the top of Telescope by means of capstan headed nuts.Telescope by means of capstan headed nuts.

3.3.Levelling head :Levelling head : Levelling head generally Levelling head generally consists of two parallel plates with 3 foot consists of two parallel plates with 3 foot screws. Upper plate is known as Tribrach and screws. Upper plate is known as Tribrach and lower plate is trivet which can be screwed on to lower plate is trivet which can be screwed on to the tripod. Levelling head has to perform 3 the tripod. Levelling head has to perform 3 distant functions :distant functions :

i) to support the telescopei) to support the telescopeii) to attach the level to the tripodii) to attach the level to the tripodiii) to provide a means for level (foot screws)iii) to provide a means for level (foot screws)

Adjustment of level :Adjustment of level :i) Temporarily Adjustments – i) Temporarily Adjustments – adjustments which adjustments which are made for every setting of a level.are made for every setting of a level.ii) Permanent adjustments- ii) Permanent adjustments- required if some error is required if some error is there in instrument. there in instrument. i) Temporary Adjustments : i) Temporary Adjustments : includesincludes

a) setting up the levela) setting up the levelb) levelling upb) levelling upc) elimination of parallaxc) elimination of parallax

a) Setting up the level :a) Setting up the level : This operation includes This operation includes fixing the instrument on the tripod and also fixing the instrument on the tripod and also approximate levelling by leg adjustment.approximate levelling by leg adjustment.

b) Levelling up :b) Levelling up : Accurate levelling is done with the Accurate levelling is done with the help of foot screws and by using plate levels. The object help of foot screws and by using plate levels. The object of levelling up the instrument is to make its vertical axis of levelling up the instrument is to make its vertical axis truly vertical.truly vertical.

c) Elimination of parallax :c) Elimination of parallax : If the image formed by If the image formed by the objective does not lie in the plane of the cross hairs, the objective does not lie in the plane of the cross hairs, there will be a shift in the image due to shift of the eye. there will be a shift in the image due to shift of the eye. Such displacement of image is termed as parallax. Such displacement of image is termed as parallax. Parallax is removed in two stages.Parallax is removed in two stages.1) 1) Focusing the eye for distinct vision of cross hairs.Focusing the eye for distinct vision of cross hairs.2) Focusing the objective so that image is formed in the 2) Focusing the objective so that image is formed in the plane of cross hairs.plane of cross hairs.

Principles of levelling :Principles of levelling :a) Simple levelling : a) Simple levelling : The operation of The operation of levelling for determining the difference in levelling for determining the difference in elevation, if not too great between two elevation, if not too great between two points visible from single position of the points visible from single position of the level is known as simple levelling.level is known as simple levelling.

PROCEDURE : PROCEDURE : Following steps are Following steps are involved.involved.

1.1.Level the instrument correctly.Level the instrument correctly.2. Direct the telescope towards the staff held2. Direct the telescope towards the staff held3. Take the reading of Central, horizontal hair of the 3. Take the reading of Central, horizontal hair of the diaphram, where it appears to cut the staff ensuring diaphram, where it appears to cut the staff ensuring that the bubble is central.that the bubble is central.4. Send the staff to next point4. Send the staff to next point5. Direct the telescope towards C and focus it again5. Direct the telescope towards C and focus it again6. Check up the bubble if central, if not bring it to the 6. Check up the bubble if central, if not bring it to the Central position by the foot screw nearest to the Central position by the foot screw nearest to the telescope.telescope.7. Take the reading of Central Horizontal cross hair.7. Take the reading of Central Horizontal cross hair.

b) Differential levelling or fly levelling :b) Differential levelling or fly levelling : This method is used in order to find the This method is used in order to find the difference in elevation between two points.difference in elevation between two points.i) If they are too far aparti) If they are too far apartii) if the difference in elevation between them is ii) if the difference in elevation between them is too great.too great.iii) If there are obstacles intervening. In such iii) If there are obstacles intervening. In such case it is necessary to set up the level in several case it is necessary to set up the level in several positions and to work in series of stages.positions and to work in series of stages.

The difference of level of the points A&B is equal The difference of level of the points A&B is equal to the algebraic sum of these difference between to the algebraic sum of these difference between the sum of back sights and sum of the fore sights the sum of back sights and sum of the fore sights i.e. i.e. ΣΣ BS - BS - ΣΣ FS FS

Booking and reduction of the levels may be done Booking and reduction of the levels may be done by following 2 methods.by following 2 methods.i) Rise and fall methodi) Rise and fall methodii) Height of collimation methodii) Height of collimation method

RISE AND FALL METHOD –RISE AND FALL METHOD –

In this method, the difference of level between two In this method, the difference of level between two consecutive points for each setting of the instrument is consecutive points for each setting of the instrument is obtained by comparing their staff readings.obtained by comparing their staff readings.

The difference between their staff readings The difference between their staff readings indicates a rise if back sight is more than foresight and a indicates a rise if back sight is more than foresight and a fall if it is less than foresight.fall if it is less than foresight.

The Rise and Fall worked out for all the points The Rise and Fall worked out for all the points given the vertical distances of each point relative to the given the vertical distances of each point relative to the proceeding one.proceeding one.

If the RL of the Back staff point is known, then RL If the RL of the Back staff point is known, then RL of the following staff point may be obtained by adding its of the following staff point may be obtained by adding its rise or substracting fall from the RL of preceding point.rise or substracting fall from the RL of preceding point.

Height of Collimation Method:Height of Collimation Method:In this method Height of Instrument In this method Height of Instrument

(H.I.) is calculated for each setting of the (H.I.) is calculated for each setting of the instrument by adding the back sight (B.S.) to instrument by adding the back sight (B.S.) to the elevation of B.M.the elevation of B.M.

Height of instrument (H.I.) = R.L. of the Height of instrument (H.I.) = R.L. of the plane of collimation plane of collimation

= R.L. of B.M.+B.S. = R.L. of B.M.+B.S.

RL of a point = H.I. – FSRL of a point = H.I. – FSOr = H.I. – IS Or = H.I. – IS

- After every back sight, there may be many - After every back sight, there may be many intermediate sights but there must be only one intermediate sights but there must be only one foresight.foresight.- The B.S. & F.S. forms the two ends of one - The B.S. & F.S. forms the two ends of one stage in levelling.stage in levelling.- Levelling should always commence from a - Levelling should always commence from a permanent B.M. and end on a permanent B.M.permanent B.M. and end on a permanent B.M.

THEODOLITETHEODOLITE

THEODOLITE - THEODOLITE - An instrument used for measuring An instrument used for measuring horizontal and vertical angles accurately is known horizontal and vertical angles accurately is known as theodolite.as theodolite.Uses of TheodoliteUses of Theodolitei) Measurement of Horizontal and vertical angles.i) Measurement of Horizontal and vertical angles.Ii) Setting out lines and anglesIi) Setting out lines and anglesiii) Optical distance measurementiii) Optical distance measurementiv) Plumbing tall buildingiv) Plumbing tall buildingv) Setting out of Railway curvesv) Setting out of Railway curvesvi) Locating the position of piers for Bridge etc.vi) Locating the position of piers for Bridge etc.vii) Geographical position fixing from observation vii) Geographical position fixing from observation of sun and stars.of sun and stars.viii) Alignment control in tunnel construction.viii) Alignment control in tunnel construction.

Types of Theodolite : Types of Theodolite : Transit theodolites are Transit theodolites are categorised into 3 types :categorised into 3 types :1. Vernier theodolite1. Vernier theodolite2. Optical Reading Theodolite2. Optical Reading Theodolite3. Digital Theodolite/Electronic Theodolite3. Digital Theodolite/Electronic Theodolite

Basically Transit Theodolite are those in Basically Transit Theodolite are those in which the telescope can revolve through a which the telescope can revolve through a complete revolution about its Horizontal axis complete revolution about its Horizontal axis in vertical plane.in vertical plane.

Components of Transit theodolite –Components of Transit theodolite –Transit theodolite consists of the following Transit theodolite consists of the following

parts :parts :1.1. Levelling HeadLevelling Head2.2. Lower Plate or Scale PlateLower Plate or Scale Plate3.3. Upper Plate or Vernier PlateUpper Plate or Vernier Plate4.4. The standard or A FrameThe standard or A Frame5.5. T-Frame or Index Bar.T-Frame or Index Bar.6.6. Plate LevelsPlate Levels7.7. TelescopeTelescope

1.1.Levelling Head -Levelling Head - Levelling Head consists Levelling Head consists of upper tribrach and lower Tribrach. Upper of upper tribrach and lower Tribrach. Upper tribrach has three arms, each arm carries a tribrach has three arms, each arm carries a levelling screw for levelling the equipment. levelling screw for levelling the equipment. Lower tribrach has got a circular hole Lower tribrach has got a circular hole through which a plumb bob may be suspended through which a plumb bob may be suspended for centering.for centering.Three distinct functions of levelling head are:Three distinct functions of levelling head are: i) to support the main part of the instrumenti) to support the main part of the instrumentii) to attach the Theodolite to the Tripodii) to attach the Theodolite to the Tripodiii) to provide a means for levelling the iii) to provide a means for levelling the theodolitetheodolite

2.2. Lower PlateLower Plate (Scale Plate) : (Scale Plate) : Lower Plate Lower Plate which is attached to outer spindle, carries a which is attached to outer spindle, carries a horizonta graduated circle, it is graduated horizonta graduated circle, it is graduated from 0-360. Each degree is further divided from 0-360. Each degree is further divided into 10 minutes or 20 minutes. Scale plate can into 10 minutes or 20 minutes. Scale plate can be clamped to any position by a clamping be clamped to any position by a clamping screw and a corresponding slow motion screw.screw and a corresponding slow motion screw.When the lower plate is tightened, the lower When the lower plate is tightened, the lower plate is fixed to the upper tribrach of the plate is fixed to the upper tribrach of the levelling head. The size of the Theodolite is levelling head. The size of the Theodolite is determined by the size of the diameter of this determined by the size of the diameter of this lower plate.lower plate.

3.3.Upper plate or Vernier Plate :Upper plate or Vernier Plate : Upper Upper plate is attached to Inner spindle axis. Two verniers plate is attached to Inner spindle axis. Two verniers are screwed to the upper plats. It carries an upper are screwed to the upper plats. It carries an upper clamp screw and tangent screw. On clamping the clamp screw and tangent screw. On clamping the upper clamp and unclamping the lower clamp, the upper clamp and unclamping the lower clamp, the instrument may be rotated on its outer spindle instrument may be rotated on its outer spindle without any relative motion between the two plates.without any relative motion between the two plates.

On the other hand if lower clamp screw is On the other hand if lower clamp screw is tightened and upper clamp screw is unclamped, the tightened and upper clamp screw is unclamped, the instrument may be rotated about its inner spindle instrument may be rotated about its inner spindle with a relative motion between the vernier and with a relative motion between the vernier and graduated scale of the lower plate. This property is graduated scale of the lower plate. This property is utilised for measuring angles.utilised for measuring angles.

44. Plate Levels -. Plate Levels - Upper plates carries two plateUpper plates carries two plate levels placed at right angles to each other. One of the levels placed at right angles to each other. One of the plate bubble is kept parallel to the trunion axis. Plate plate bubble is kept parallel to the trunion axis. Plate levels can be centred with the help of foot screws.levels can be centred with the help of foot screws.

5. Telescope –5. Telescope – Telescope is supported on the pivots Telescope is supported on the pivots of the trunion axis which affords its movement in the of the trunion axis which affords its movement in the vertical plane.vertical plane.

IMPORTANT DEFINITIONS –IMPORTANT DEFINITIONS –I) Line of CollimationI) Line of Collimation - the line which passes - the line which passes through the Intersection of the cross hairs of the eye through the Intersection of the cross hairs of the eye piece and optical centre of the objective and its piece and optical centre of the objective and its continuation is called as line of collimation. This is also continuation is called as line of collimation. This is also known as line of sight.known as line of sight.

ii)ii)Transiting -Transiting - The process of turning the The process of turning the telescope in vertical plane through 180 deg. telescope in vertical plane through 180 deg. about its horizontal axis is known as about its horizontal axis is known as transiting.transiting.

iii) Swing -iii) Swing - A continuous motion of telescope A continuous motion of telescope about the vertical axis in horizontal plane is about the vertical axis in horizontal plane is called swing. The swing may be in either called swing. The swing may be in either direction i.e. Right swing or left swing.direction i.e. Right swing or left swing.

iv) Face left observation –iv) Face left observation – When vertical circle is on When vertical circle is on the left of the telescope at the time of observation, the the left of the telescope at the time of observation, the observations are called face left observation.observations are called face left observation.

v) Face right observation –v) Face right observation – When vertical circle is on When vertical circle is on the right of the telescope at the time of observation.the right of the telescope at the time of observation.

TEMPORARY ADJUSTMENT OF TEMPORARY ADJUSTMENT OF THEODOLITETHEODOLITE1) Setting up the Theodolite over the station1) Setting up the Theodolite over the station2) Levelling up the theodolite2) Levelling up the theodolite3) Elimination of the parallax3) Elimination of the parallax

1.1.Setting up :Setting up : Operation of setting up a theodolite Operation of setting up a theodolite includes:includes:a) a) centering the theodolite over the ground markcentering the theodolite over the ground markb) approximate levelling with the help of tripod legs.b) approximate levelling with the help of tripod legs.

2. Levelling up of theodolite2. Levelling up of theodolite The operation of making the vertical axis truly The operation of making the vertical axis truly vertical is known as levelling of Theodolite.vertical is known as levelling of Theodolite.

i) Turn the horizontal plate until the i) Turn the horizontal plate until the longitudinal axis of the plate level is longitudinal axis of the plate level is approximately parallel to a line joining any two approximately parallel to a line joining any two levelling screwslevelling screws..

ii) ii) Bring the bubble to the centre of its run by turning Bring the bubble to the centre of its run by turning both foot screws simultaneously in opposite directions both foot screws simultaneously in opposite directions either inwards or outwards. The movement of the left either inwards or outwards. The movement of the left thumb indicates the direction of movement of bubble.thumb indicates the direction of movement of bubble.

iii) Turn the instrument through 180iii) Turn the instrument through 18000 in azimuth. in azimuth.

iv) Note the position of the bubble. If it occupies a iv) Note the position of the bubble. If it occupies a different position, move it by means of the same two foot different position, move it by means of the same two foot screws to the approx. mean of the two positions.v) Turn screws to the approx. mean of the two positions.v) Turn the theodolite through 90 in azimuth so that the plate the theodolite through 90 in azimuth so that the plate level becomes perpendicular to the previous position.level becomes perpendicular to the previous position.

vi) With the help of third floor screw, move the bubble to vi) With the help of third floor screw, move the bubble to the approx. mean position already indicated.the approx. mean position already indicated.

vii) Repeat the process until the bubble, retains vii) Repeat the process until the bubble, retains the same position for every setting of the the same position for every setting of the instrument.instrument.3. Elimination of Parallax :3. Elimination of Parallax : Elimination of parallax Elimination of parallax may be done by focusing the eye piece for distinct vision may be done by focusing the eye piece for distinct vision of cross hairs and focusing the objective to bring the of cross hairs and focusing the objective to bring the image of the object in the plane of cross hairs.image of the object in the plane of cross hairs.

Measurement of Horizontal AngleMeasurement of Horizontal Angle

Procedure : to measure a Horizontal Angle Procedure : to measure a Horizontal Angle ABC between BA & BC the following ABC between BA & BC the following

procedure is followed.procedure is followed.

1.1.Set up, Centre and level the theodolite over Set up, Centre and level the theodolite over the ground point B.the ground point B.

2. Loosen the upper plate, set the vernier to 2. Loosen the upper plate, set the vernier to read zero and clamp the upper clamp.read zero and clamp the upper clamp.

3. Loosen the lower plate and swing the 3. Loosen the lower plate and swing the telescope until the left point A is sighted. telescope until the left point A is sighted. Tighten the lower clamp. Accurate bisection Tighten the lower clamp. Accurate bisection of the arrow held on the Point A is done by of the arrow held on the Point A is done by using the lower tangent screw. Read both the using the lower tangent screw. Read both the vernier and take the mean of the reading.vernier and take the mean of the reading.

4. 4. Unclamp the upper plate and swing the Unclamp the upper plate and swing the telescope in clockwise direction until point C is telescope in clockwise direction until point C is brought in the field of view. Tighten the upper brought in the field of view. Tighten the upper clamp and bisect the mark of C accurately, clamp and bisect the mark of C accurately, using the upper clamp tangent screw.using the upper clamp tangent screw.

5. Read both the verniers and take the mean 5. Read both the verniers and take the mean of readings. The difference of the means of the of readings. The difference of the means of the reading to C to A is the required angle ABC.reading to C to A is the required angle ABC.

6. 6. Change the face of the instrument Change the face of the instrument and repeat the show procedure, the and repeat the show procedure, the measure of the angle is again obtained measure of the angle is again obtained by taking the difference of the means of by taking the difference of the means of the readings to C&A on face right.the readings to C&A on face right.

7. The mean of the two measures of the 7. The mean of the two measures of the angle ABC on two faces is the required angle ABC on two faces is the required value of the angle ABC.value of the angle ABC.

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