1.0 INTRODUCTION

Tachymetry is a system of rapid surveying, by which the positions, both horizontal

and vertical, of points on the earth surface relatively to one another are determined

without using a chain or tape or a separate levelling instrument.

These difficulties led to the introduction of tachymetry, in which, instead of the

prism pole formerly employed to mark a point. This is marked with heights from

the foot, and is graduated according to the form of tachymetry in use.

The azimuth angle is determined as formerly. Thus all the measurements requisite

to locate a point both vertically and horizontally with reference to the point where

the tachymetry is centred are determined by an observer at the instrument without

any assistance beyond that of a man to hold the prism pole.

There are several different types of tachymetry system, including the stadia,

subtense bar, and optical wedge systems. The total station/EDM survey system

method is the most commonly used and incorporates a total station/EDM controlled

by one operator and a pole with prism, measured markings on it held by another

surveyor at a distance. A standard transit is basically a telescope with cross-hairs for

sighting a target [Figure 1.1] the telescope is attached to scales for measuring the

angle of rotation of the telescope (normally relative to north as 0 degrees) and the

angle of inclination of the telescope (relative to the horizontal as 0 degrees). After

rotating the telescope to aim at a target, one may read the angle of rotation and

the angle of inclination from a scale.There are 3 steps to complete the work :-

a) Traverseb) Levelling processc) Detailing

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Figure1.1 : The view in Telescope

1.1 TRAVERSE

Traversing is that type of survey in which a number of conncted survey

lines form the frameworks and the directions and lengths of the survey

lines are measured with the help of an angle measuring instrument and a

tape or chain respectively. There are two types of traverse surveying

[Figure 1.1.1]. Closed traverse when the lines from a circuit which

ends at the starting point, it is known as closed traverse. Open

traverse when the lines from a circuit ends elsewhere except starting

point, it is said to be an open traverse. Suitability are the closed

traverse is suitable for locating the boundaries of lakes, woods, etc

and for survey of large areas.

The open traverse is suitable of surveying a long narrow strip of land

as required for a road of canal or the coast line. Difference between

chain and traverse surveying. Traverse survey differs from chain

surveying in the arrangement of the survey survey lines is not limited

to any particular geometric figure as in chain surveying, where a

system of connected triangles forms the fundamental basis of the

skeleton. Also, check line etc. are not necessary in traverse as the

traverse line may be arranged near the details, the detail etc. are

directly located with respect to the survey lines either by offsetting

or by any other method.

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Figure 1.1.1: Closed

traverse & Open traverse

1.2 LEVELLING

Levelling is the general term applied to any of the various processes

by which elevations of points or differences in elevation are

determined [Figure 1.2.1]. Leveling result are used to design highways,

railroads, canals, sewers, water supply systems, having grade lines

that best conform the existing topography, to lay out construction

projects according to planned elevations, to calculate volume of

earthworks and other materials and to investigate drainage

characteristics of an area. Levelling is a branch of surveying, the

object of which is to find the elevation of a given point with respect

to the given or assumed datum. Levelling is the measurement of geodetic

height using an optical leveling instrument and a level staff or rod

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with a numbered scale. Common levelling instruments include the spirit

level, the dumpy level, and the laser level.

Leveling is more accurate since elevation differences are measured not

calculated. Two readings are taken at each position of the automatic

level: a backsight towards a station located before the level on the

traverse and a foresight to the next station on the traverse. Thus the

stadia rod occupies two stations, before and after the level on the

survey.  The difference in elevation between successive stations if the

difference between the backsight and the foresight read from the stadia

rod.  For each position of the level, the lengths of the foresights and

backsights should be approximately the same since accuracy is a

function of the distance of a sighting.  The level operator should

anticipate the distance to the next station and set up the level midway

along this distance (note: the distance that can be sighted decreases

with increase in slope, since the stadia rod will disappear above or

below the level line of sight).  The lengths of backsight and foresight

can be paced by the rod person or measured by the interval between the

upper and lower cross hairs (tachymetry).

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Figure

1.2.1 : Differential levelling

1.3 DETAILING

The actual depiction of the features to be shown on the map can be

performed either on the ground or, since the invention of photography,

aviation, and rocketry, by interpretation of aerial photographs and

satellite images. On the ground the framework is dissected into even

smaller areas as the surveyor moves from one point to another, fixing

further points on the features from each position by combinations of

angle and distance measurement and finally sketching the features.

Detail can generally be subdivided into either:

· Natural or man made features whose extent and shape can be shown onthe plan to scale;

· Natural or man made features whose extent cannot be shown on the plan

to scale, but which are sufficiently prominent to be of importance.

Detail of this type is normally depicted by a standardised symbol.

This detail can be further classified as either:

· Definite Detail : Normally man made features such as buildings,roads,

walls and fences whose position can easily be defined and checked both

on the ground and on the plan.

· Indefinite Detail : Typically, natural features such as areas of vegetation

or water, which are incapable of exact definition or are liable to

change.

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· Overhead Detail : Detail which constitutes no obstruction at ground

level. (e.g.overhead gantries, power lines etc.)

· Underground Detail: Detail located below ground surface level.(E.g.water

pipes, sewer pipes etc.)

· Interior Detail : Internal features of a building which may or may not

determine property boundaries. Normally internal features shown on

Ordnance Survey maps are restricted to the divisions between buildings,

where they can be seen to extend through the whole building, and to

roof level. Surveyors may occasionally be called upon to survey

internal floor layouts for land registration cases, particularly when

there are overlapping extents at different levels – typically in

veryold properties.

1.4 SETTING OUT

A definition of setting out, often used, is that it is the reverse of

surveying. Whereas surveying is a process for forming maps and plans of

a particular site or area, setting out begins with plans and ends with

the various elements of a particular plan correctly positioned on site.

However most techniques and equipment used in surveying are also used

in setting out i.e. while surveying may be the opposite of setting out,

the processes and instruments are almost identical.

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The International Organisation for Standardisation (ISO) define setting

out as: Setting out is the establishment of the marks and lines to

define the position and level of the elements for the construction work

so that works may proceed with reference to them. This process may be

contrasted with the purpose of surveying which is to determine by

measurement the position of existing features.

-Setting out is one application of surveying.

-Most of the techniques and equipment used in surveying are also used

in setting out.

-Mistakes in setting out can be costly.

-For setting out to be undertaken successfully good work practices

should be employed.

-There are three parties involved in the construction procedures: the

employer, the engineer and the contractor.

-Although the engineer checks the work, the setting out is the

responsibility of the contractor.

-The cost of correcting any errors in the setting out has to be paid

for by the Contractor, provided the engineer has supplies reliable

information in writing.

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2.0 EQUIPMENT

2.1 TOTAL STATION

A total station [Figure 2.1.1] is a combination electronic transit and

electronic distance measuring device (EDM). With this device, as with a

transit and tape, one may determine angles and distances from the

instrument to points to be surveyed. With the aid of trigonometry, the

angles and distances may be used to calculate the actual positions (x,

y, and z or northing, easting and elevation) of surveyed points in

absolute terms. This can be done for both vertical and horizontal

angles.

Vertical angles are required for the calculation of elevation of

points for example the reduction of slope distance to the horizontal.

Horizontal angles are required to obtain the relative direction to a

survey control station or points of detail.

The instrument can be made to read to the nearest whole 1” which is

considered accurate enough for most engineering purposes.

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Figure 2.1.1 :

Total station

2.2 LEVEL INSTRUMENT

Level  instrument is an optical instrument used to establish or check

points in the same horizontal plane [Figure 2.2.1]. It used

in surveying to measure the height of distant points in relation to

a bench mark. It consists of a telescope fitted with a spirit level

and, generally, mounted on a tripod. It is used in conjunction with a

graduated rod placed at the point to be measured and sighted through

the telescope.

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Figure 2.2.1 : Level instrument

2.3 TRIPOD

Tripod is used to setup digital Total Station and level instrument

[Figure 2.3.1]

Figure 2.3.1 : Tripod

2.4 PRISM

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The reflecting prism is a cylindrical device about the diameter of a

soft-drink can and about 10 cm [figure 2.4.1]. In height; at one end is

a glass covering plate and at the other is a truncated cone with a

threaded extension. It is normally screwed into a target/bracket on the

top of a pole; the pointed tip of the pole is placed on the points to

be surveyed.

Figure 2.4.1 : Prism

2.5.1 UMBRELLA ROOFING NAIL (Piket)

Umbrella roofing nail is used to mark station of the traverse [Figure

2.5.1].

\

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Figure 2.5.1 :

Umbrella roofing nail

2.6.1 POLE

Pole is an object where Total Station want to target for reading

[Figure 2.6.1].The prism is mounted on a pole of known height; the

mounting bracket includes aids for aiming the instrument. Although the

tip of the pole is placed on the point to be surveyed, the instrument

must be aimed at the prism. Since the

prism is directly above the

tip, the height of the pole may be

subtracted to determine the

location of the point.

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Figure

2.6.1 : Pole

2.7.1 MEASURING TAPE

Measuring tape is used to measure the height of theodolit [Figure

2.7.1].

Figure 2.7.1 :

Measuring tape

3.0 PROCEDURE OF WORK

3.1 TRAVERSE

A) CENTERING THE TOTAL STATION

The instrument must be vertically above the survey station to ensure

that horizontal angle observations are correct. The steps are

as follows:

i. Start with a prism to get it approximately right above the survey

station.

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ii. Using the foot screws, move the optical plummet cross hairs on to

the survey station.

iii. Roughly level the instrument using the legs of the tripod – the

total station should stay almost on target.

iv. Level with foot screws. Move instrument above target; repeat level

and move until done.

B) LEVELLING THE TOTAL STATION

i. Turn bubble parallel to two foot screws, to bring the horizontal

bubble to the centre of its run by moving the foot screws in

opposite directions (the bubble moves in the direction of your left

humb).

ii. Turn the instrument through 90º and bring the bubble to the centre

of its run by adjusting the third foot screw only.

iii. Turn the instrument through a further 90º to check the adjustment

of the plate bubble.

iv. If the bubble remains in centre, then it is adjusted.

v. If not, move it back one-half of the movement from the centre and

re-adjust for a further 90º turn.

vi. Repeat the whole procedure; assuming this is the correct, the

bubble will stay in a stationary position.

vii. The bubble must remain in the same place in the tube during a

360ºrotation of the instrument.

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viii. If the stationary position of the bubble is still off the centre,

then a permanent adjustment should be made.

C) TRAVERSE FIELD WORK

Traversing is carried out with three(3) tripod, one(1)tripod is for

the instrument and the other two(2) are for the back and front

stations. A minimum of three people is required in a traversing team.

The leader of the team, setting up and reads the instrument, while

the 2nd person has the important job of recording the readings on the

booking sheet. The 3rd person has the task of moving and setting up

the prism as the traverse progresses. There are several steps which

should be followed that will lead to a smooth traverse.

i. Four picket(station) were established at the proposed site.(peg 1, peg 2, peg 3 & peg 4).

ii. The total station was plumbed over peg 2 and accurately leveled.

Prism were plumbed over peg 1&3.

iii. Set the total station to read zero and target peg 1.

iv. Distance was measured by pointed the staff at peg 1, and vertical

and horizontal angles are displayed in relation to markings on the

staff, which determines distance and elevation. The reading was

taken and entered in the field book. Distance between peg 2 and 3

also done with the same technique.

v. Record face left horizontal reading to back station(peg 1).

vi. Turn instrument and sight front station.

vii. Record face left horizontal reading to front station(peg 3).Polisas Page 15

viii. Transit the instrument to change to the face right setting.

ix. Record face right horizontal reading to front station(peg 3).

x. Turn instrument to face back station.

xi. Record face right horizontal reading to back station(peg 1).

xii. The total station was moved to peg 3. Prism were plumbed over peg

2 and 4. Peg2 was sighted on face left with total station set to

the reading taken from step 9.

xiii. Peg 4 was sighted and the horizontal angle was taken. The

instrument was set to face right and peg 4 was sighted again. Then

peg 2 was sighted and the reading was taken.

xiv. Step 2-11 was repeated on peg 4 & peg1.All readings were observed and recorded

3.2 LEVELLING

a) Survey the site for putting the picket signs.

b) Level instrument must be properly fitted and used the water coil

to determine the position of level equipment.The level is set up

at some convenient position and BS of 0.325m is taken to TBM

1(44.984m).

c) The position of the change point is at Station 3, the staff is

moved to this and a FS of 4.101m is taken.

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d) While the staff remains at station 3, the instrument is moved to

another position. A change point must be used in order to reach

station 1 & 2.

e) The staff is then moved to station 2 and intermediate sights of

1.426m are taken.

f) A BS of 1.204m is taken from the new level position to the staff

at station 1.

g) While the staff remains at station 1, the instrument is moved to

another position. The position of the change point is at Station

4, the staff is moved to this and a FS of 1.260m is taken.

h) The instrument is moved to another position and after that the

staff is moved to CP1 and readings of 0.855m (FS) are taken where

CP1 is another change point.

i) The last step is move to a position and a BS of 4.260m taken to

CP1 and a FS of 1.445m is taken to TBM 1. The final staff position

is at a TBM 1, this is most important as all levelling field work

must start at and end at a bench mark – otherwise it would be

difficult to detect errors when levelling.

j) Calculating reduced levels using the height of collimation method

and also calculating the correction and misclosure.

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3.3 DETAILING

a) Setting up the total station by putting it on the tripod stand

at station 1.

b)Focus on the surveying point using optical plummet eyepiece.

Center the surveying point by adjusting the leg of the tripod.

c)Center the bubble in the circular level and plate level by using

foot screw and tripod legs.

d)Do the temporary adjustment.

e)Record the instrument height (H.I.).

f)Set the back bearing from station 1 to station 4.

g)Loosen horizontal and vertical clamp; swing the telescope

direction roughly to the prism which the prism is being placed

vertically at each corner of the building, trees, spot height and

all the details around the station.

h)Using the slow motion screw horizontal and vertical, place to the

reflection point on the prism.

i)The telescope is pointed at the prism, and vertical and horizontal

angles are displayed in relation to markings on the prism, which

determines distance and elevation. Recorded the reading in the

form tachymetry.

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j) Record the vertical and horizontal distance in the form

tachymetry.

k) After that,remove the equipment level at any other point and

repeat step 2 to step 10.

l) The same was done at others the station( 2, 3, & 4).

3.4 SETTING OUT (Pipeline)

This operation falls into the first category of setting out. General

considerations that sewers normally follow the natural fall in the land

and are laid at gradients which induce self-cleansing velocity.

a) Horizontal control: the working drawings will show the directions

of the sewer pipes and the positions of the manholes. The line of

the sewer is normally pegged at 60m intervals using coordinate

methods of positioning from reference points or in relation to

existing detail. The direction of the line can be sighted using a

levelling instrument and pegs.

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b) Vertical control: involves the erection of sight rails some

convenient height above the invert level of the pipe.

c) Erection and use of sight rails: the sight rail uprights are

hammered firmly into the ground, usually offset from the line

rather than straddling it. Using the TBM2 (R.L 45.216) and

levelling equipment, the reduced levels of the tops of the

uprights.

d) Where the natural slope of the ground is not approximately

parallel to the proposed pipe gradient, sight rails can be used to

control the dept of excavation.

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4.0 PRACTICAL DATA

4.1 TRAVERSE

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4.2 LEVELLING

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4.3 DETAILING

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4.4 SETTING OUT

(Pipeline)

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4.5 DRAWING

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5.0 DISCUSSION

A standard transit is basically a total station with cross-hairs for sighting a target;

the total station is attached to scales for measuring the angle of rotation of the

telescope (normally relative to north as 0 degrees) and the angle of inclination of

the telescope (relative to the horizontal as 0 degrees). After rotating the telescope to

aim at a target, one may read the angle of rotation and the angle of inclination

from a scale. The electronic transit provides a digital read-out of those angles

instead of a scale; it is both more accurate and less prone to errors arising from

interpolating between marks on the scale or from mis-recording. The readout is also

continuous; so angles can be checked at any time.

The various elements of the scheme must be correct in all three

dimensions both relatively and absolutely, that is each must be its

correct size, in its correct plan position and correct reduced level

In this session we learnt to:

a) Understand the basic concepts of Optical Distance Measurement.

b) Calculate the reduce level of point by using the tachymetry

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system.

c) Understand the procedure to implement the field work.

d) Show the steps to process the observation data and determines

the errors.

e) Describe the application of tachymetry in land surveying.

f) Describe various tacheometric methods.

g) Carry out tachymetry surveying.

h) Understand the roles of the various different types of personnel

who are involved in the setting out process.

i) Understand the aims of setting out.

j) Refer to the different types of plans that may be used in the

setting out process.

k) Appreciate the good working practices that should be undertaken

in order that the aims of setting out can be achieved.

l) Understand the procedures required to ensure that the horizontal

and vertical control requirements of setting out operations can

be met.

m) Set out design points on site by a number of methods.

n) Apply horizontal and vertical control techniques to second-stage

setting out operations.

o) Appreciate the application of laser instruments in surveying and

setting out.

6.0 CONCLUSION

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During the traverse, the horizontal angles, vertical angle and

distances are measured. Horizontal angles are used in determining

azimuths and vertical angles are used in determining the deferent in

height between stations. The distance is used in conjunction with the

horizontal and vertical angles to determine coordinates and height. For

traverse surveying of low relative accuracy, where only horizontal

angles and distances are required, the stadia method is a useful rapid

method. Tachymetry is used for :

a) Preparation of topographic map where both horizontal and vertical

distances are required to be measured;

b) Survey work in difficult terrain where direct methods of

measurements are inconvenient;

c) Reconnaissance survey for highways and railways etc;

d) Establishment of secondary control points.

There are two main aims when undertaking setting out operations:

a) The various elements of the scheme must be correct in all three

dimensions both relatively and absolutely, that is each must be

its correct size, in its correct plan position and correct reduced

level

b) Once setting out begins it must proceed quickly with little or no

delay in order that the works can proceed smoothly and the cost

can be minimised. It must always be remembered that the

contractors main commercial purpose is to make a profit –

therefore setting out needs to be done efficiently.

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7.0 REFERENCE

a)Panel Buku nota POLISAS CC201b)Arthur Bannister et al “Surveying” 7th Ed Longman 1998, chapter 11.

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