Week 9 Tacheometry Survey2

8/10/2019 Week 9 Tacheometry Survey2

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With Wisdom, We Explore

TACHEOMETRIC SURVEY

Mohd Effendi Daud (Dr. Sc)B.Surv (UTM, Malaysia) Msc (UTM, Malaysia), Dr. Sc (Nagoya Univ., Japan)

(Geomatic Division)

Faculty of Civil & Environmental Engineering,

Universiti Tun Hussein Onn Malaysia, 86400 Batu Pahat, Johor, MALAYSIA.

Phone : +6074537363; +60197853740; Fax : +6074537060

E-mail : [email protected]

Web: http://www.fkass.uthm.edu.my/
mailto:[email protected]://www.fkass.uthm.edu.my/http://www.fkass.uthm.edu.my/mailto:[email protected]


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INTRODUCTION

This method of survey consists of using either a level,

theodolite, total station, or specially constructed

tacheometer to make cross hair intercept reading ona leveling staff. As the angle subtended by the

crosshairs is known, the distance can be calculated.


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DEFINITION

o Tacheometry is an optical solution to the

measurement of distance and elevation

(vertical distance).

o The word is derived from the Greek Tacns,

meaning swift, and metrot, meaning a

measure.


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METHODS OF

TACHEOMETRY

Present day methods of tacheometry can be

classified in one of the following three groups.

The last two groups will not be cover in theselectures.

Stadia System,

Electronic Tacheometry,

Subtense Bar System, and

Optical Wedge System.


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STADIA SYSTEM

In stadia method, a theodolite is set up at one

station and staff is held at another station.

The staff intercept (S)which is the difference

between the upper stadia and the lower

stadia hair is measured.

The vertical angle ()is also measured.


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STADIA SYSTEM

The horizontal distance (D)between the

Center of Instrument and staff stations is

computed using staff intercept (S)and thevertical angle ()


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There are two types of stadia method

Fixed Hair Method

In fixed hair method, the vertical spacing between

upper and lower stadia hairs, called stadia interval I, is

fixed, while the staff intercept (S) varies depending

upon horizontal distance between the instrument

station and the staff station.

Movable Hair Method

STADIA SYSTEM


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The fixed hair method is the most commonly

employed method for tacheometric measurements.

Figure 1.0 shows the types of diaphragms used in a

fixed hair stadia tacheometer (theodolite).

STADIA SYSTEM

Fig. 1.0: Types of diaphragms


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In stadia method, the staff is held vertical, the

line of sight may be horizontal or inclined

either in upward direction or downwarddirection.

There can be three cases as given below:

Line of sight horizontal, Line of sight inclined upward, and

Line of sight inclined downward.

STADIA SYSTEM


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Line of Sight Horizontal

Let us assume that the line of sight is horizontal. Figure 2.0

shows the outline of telescope with its axis horizontal. The

staff is held vertically.

STADIA SYSTEM

A, B & X: positions of lower, upper, and

middle hair the staff.

a, b & x: positions of lower, upper, and

middle hairs

ab: i (stadia interval)c: distance from object lens to the center

of the instrument

AB: S (staff intercept)

D: distance between the instrument &

staff


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STADIA SYSTEM

Line of Sight Horizontalab

AB

V

U

ox

OX

From the diagram, triangles AOB, aOb are similar

From the lens equation:

fVU

111

Multiply both sides by Uf:

ffV

UU

From the equation 1.0 and 2.0:

ffab

ABU ff

i

SU fS

i

fU

The horizontal distance:

)( cfSi

fD

cUD

If multiplicative constant, C=f/i, and additive constant, K =f + c,

The tacheometric distance formula may be stated as:KCSD


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Line of Sight Inclined Upward

Distance and Elevation Formula

The theory discussed so far, in The Stadia System, all

applies to the situation where the staff is held

vertically and the line of sight of the telescope is

horizontal. It is very seldom, however, that this situation occurs

in practice

STADIA SYSTEM


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Generally a theodolite is sighted to a level staff held

vertically (by use of a bubble), which gives rise to the

situation below.

STADIA SYSTEM


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STADIA SYSTEM

,1 KCsD cos1 ss

coscos

cos

2 kCs

DS

Let the actual distance between upper and lower

stadia be Sand the required projection of it at

right angles to IQ be s1

sin2

2sin

sinsincos

sin

kSc

kCs

DV

2sin50

cos100 2

sV

sS

but

Now

Also

In practice,


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STADIA SYSTEM

CLVHIH

The difference in height between

The two points is given by:

And the Relative Level (R.L) of

The points is given by

CLVHIRLRL A


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ELECTRONIC

TACHEOMETRIC

Used a Total Station, able to read distance byreflecting off a prism.

The stadia procedure is used less and less often

these days, more commonly geomatic engineers orcivil engineers use a Total Station

This instrumentation has facilitated the developmentof this method of detail and contour surveying into avery slick operation.

It is now possible to produce plans of large areasthat previously would have taken weeks, in a matterof days.


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ELECTRONIC

TACHEOMETRIC

HTVHIRLRL

DS

A

cos


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DETAILING & BOOKING

Tacheometric surveys are generally conducted for

contouring, and plotting the details of the area on

undulating ground.

There are two main steps in tacheometric surveys:

Running a traversing around the area to be surveyed,

Locating details and elevations of the features in the area

with reference to the traverse stations


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DETAILING & BOOKING

Figure above shows a part of the traverse with three stations A, B and C and

Some features in the area. The following observation procedure is adopted

For detailing.


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Procedure

Set up the instrument at a station (say station B), centre

and level it accurately.

Measure the height of instrument (HI) from the top of the

peg at the station to the centre of the trunion of the

instrument.

Orientate the instrument correctly with respect to a

reference line (traverse line, BA) whose bearing from the

station is already known by traversing.

DETAILING & BOOKING


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Procedure cont.,

Take the pole reading held vertical on the nearest

available temporary benchmark (TBM) to determine the

reduced level of the instrument station.

Located the detail points around the traverse station (B) as

given below:

Observe the horizontal angle between the reference line and the

line from the instrument station towards the point of interest.

Observe the vertical angle and the pole readings.

Repeat the steps above for all the points of interest.

DETAILING & BOOKING


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WORK EXAMPLE 1

Determine the difference in elevation and the horizontal distance

between the points A and B from the following observations.

The instrument was set up at O at 1.500 mheight, and the RL of

Station O was 12.635 m.

Calculate the following:

(i) Horizontal distances OA and OB

(ii) RLs of station A and B

(iii) Difference in elevation between A and B


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The following observations obtained from tacheometry survey.

WORK EXAMPLE 2

The RL of P is 58.775 m. Determine the distances PQ and QR and the

Reduced levels of Q and R.


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ACCURACY AND TYPES OF

ERRORS

Besides all the errors discussed in the topic on

total station, there are four (4) specific

sources of errors needed to be mentioned intacheometric observations

Staff readings

Tilt of the pole or staff Vertical angle, and

Horizontal angle


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PLOTTING OF

TACHEOMETRIC DATA

The process of tying the topographic details to

the control stations fixed by traversing is

called detailing.

A map is the final

product of a

tacheometric survey.


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Type of Maps

Maps produced or normally used by engineers may

fall into one of the following three categories:

Topographic maps 1:50,000 to 125,000 which shows

natural and cultural features of an area.

Plans 1:10,000 or larger, which shows boundaries and

main features like roads, bridges and main buildings.

Detail survey plans (construction plans) at 1:1,0001:250

PLOTTING OF

TACHEOMETRIC DATA


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Plotting Methods

Can be carried out manually, or by employing

computer aided design (CAD) systems.

The procedure consists fundamentally of plotting

individual points, regardless of which method is

used.

Lines are drawn from point to point to show the features. Points can be plotted in different ways using distances and

directions, and lines can be scaled and plotted directly.

PLOTTING OF

TACHEOMETRIC DATA


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Plotting Methods

There are two main methods of plotting details as

discussed below: Plotting by Coordinates

Plotting by Angle/bearing and Distances.

PLOTTING OF

TACHEOMETRIC DATA


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Map Layout

The surveyed area should be plotted to fit neatly in

the centre of a map sheet at the largest possible

scale.

North Direction

Every map must display a north line for orientation purpose.

Topographic Symbols (Legends) Standard symbols should be used to portray topographic features.

Title of Map

Place title of the map where it is balanced on the sheet.

PLOTTING OF

TACHEOMETRIC DATA


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Map

Layout

PLOTTING OF

TACHEOMETRIC DATA


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CONTOURING AND CROSS-

SECTIONSMohd Effendi Daud (Dr. Sc)

B.Surv (UTM, Malaysia) Msc (UTM, Malaysia), Dr. Sc (Nagoya Univ., Japan)

(Geomatic Division)

Faculty of Civil & Environmental Engineering,

Universiti Tun Hussein Onn Malaysia, 86400 Batu Pahat, Johor, MALAYSIA.Phone : +6074537363; +60197853740; Fax : +6074537060

E-mail : [email protected]

Web: http://www.fkass.uthm.edu.my/
mailto:[email protected]://www.fkass.uthm.edu.my/http://www.fkass.uthm.edu.my/mailto:[email protected]


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CONTOURING

For planning and development of an

engineering project, the engineer requires the

topographic of the natural ground. An understanding of contours is therefore

essential in the interpretation of surface

topography. Some basic understanding of contours is as

follow:


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CONTOURING


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A contour is an imaginary line connecting allpoints of the same elevation above or below adatum.

Contours of different elevation cannot cross eachother except in the case of overhanging cliff or acave.

The height between successive contours is called

the contour interval Its value depends on the variation in height of the area

being contoured.

The contour interval is kept constant for a plan or map

CONTOURING


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The plan spacing between contour line indicates

the steepness of slopes.

Closely spaced lines indicated a steep slope

Widely spaced lines indicate a gentle slope.

CONTOURING


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CONTOURING


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Production of contours

There are TWO types of contouring method:

Direct Methods, and Indirect Method:

from random spot heights

from a grid of spot heights

CONTOURING


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CONTOUR INTERPOLATION &

PLOTTING

There are THREE methods of interpolating

contours:

Mathematical calculation, Graphical method, and

Estimation method.


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PROFILE AND CROSS-

SECTIONS

Profiles (longitudinal sections) is generally carriedout along the center line of a proposed alignmentse.g. highways, railways, pipelines or canals.

The profile is usually plotted with the vertical scalemuch larger than the horizontal scale.

The term cross-sectioning refers to a relatively shortprofile view of the ground, which is drawn

perpendicular to the route center line of a highwaysor other linear type projects.


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Cross-section drawing are particularly important for

estimating the earthwork volumes needed to

construct a roadway, canal, railroad, etc.

They show the existing ground elevations, the

proposed cut or fill side slopes, and the grade

elevation for the road base.

For one route profile, there are many cross-sections;a km-long route, for example, will have more than

100 cross-sections every 50 m.

PROFILE AND CROSS-

SECTIONS


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Pheewww! End of Part V

Week 9 Tacheometry Survey2

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