tachimetry.docx

8/10/2019 Tachimetry.docx

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FIELD WORK 1 : TACHIMETRY

1.0 INTRODUCTION

a. Horizontal Sight

Based on principledistance-elevation

stadia formulae derived for the horizontalsights.

Figure 1 : Measurement of horizontal sight method (based on stadia principle)

b. Inclined SightThis method is frequently required to reduce the inclined observations into horizontal

distance and difference in elevation.

PURPOSE :

Know the following field work :

a. Tachymentry by vertical staff fixed stadia method .

1.2.1 Follow standard procedure

1.2.2 Conduct the task according to the requirement

1.2.3 Accomplish the task within a given time frame.

1.2.4 Document the task and produce the report.

c. Tangential System

In this method , the stadia hairs are not used, the readings being taken against the

horizontal cross-hair. To measure the staff intercept, two pointings of the instruments

are, therefore , necessary .


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2.0 OBJECTIVE

a. Horizontal Sight

To understand the common principle of tachymetry horizontal sight method.

b. Inclined Sight

i. Revise the basic princples of traversing and experience of the field works

procedure, so that students are able to establish the control points by surveying

approach with minimize errors and practicable.

ii. To develop skill in using EDM thus could be explored more function that

assist on the instrument .


To know the following field work

b. Tachymetry by tangential

1.2.1 Follow the standard procedure

1.2.2 Conduct the task according to the requirement

1.2.3 Accomplish the task within a given time frame

1.2.4 Document the task and procedure the report.


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3.0 INSTRUMENT

Figure 2 :Theodelite

A Theodelite is a precision instrument for measuring angles in the horizontal and vertical

planes.

Figure 3 :Staff Level

Staff Level is a graduated rod used by surveyors to measure differences in level.

Figure 4 :Tripod

Tripod is used to setting up the theodelite and also approximate adjust the bubble by leg

adjustment.


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Figure 5 : Compass

Prismatic Compass is one of the two main kinds of magnetic compasses included in the

collection for the purpose of measuring magnetic bearings.

Figure 6 : Wooden Peg

Wooden Peg is usually used to mark or set in a certain point.

Figure 7 : Hammer

Hammer is used to hammered the wooden peg into the ground.


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4.0 FIELD WORK PROCEDURE

a. Horizontal Sight

Figure 8 : Traverse Tachimetry

1. A relatively flat area is selected and placed with three point of station.

2. Known the distance to be measured which are 1-2, 2-3 and 3-1.

3. The instrument at point 2 is set up and levelled . Point 1 is the reference object and

point 3 of the line to be measured. The theodolite vertical angle is set as 900000 4. The levelling staf is placed over the other end (point 1) of the line.

5. The bearing 2 to 1 in the theodolite is set and point 1 is observed.

6. Stadia hair readings is measured.(upper, middle and lower)

7. Then , levelling staff is placed over point 3 and the bearing and stadia readings is

observed. (upper, middle and lower)

8. The distance between point 2 to 1 and point 2 to 3 is compute.

Horizontal Sights

Hd = Ks + C

Where :Hd = horizontal distance

K = stadia interval factor =100

s = stadia intercept (upper rdg. lower rdg.)

c = stadia additive = 0 (for internal focusing telescope)


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b. Inclined Sight

(I) TRAVERSE CONTROL

Traverse are a series of established stations tied together by angle and distance. A

traverse is a form of control survey that is used in a wide variety of engineeringand property surveys. A closed traverse is beginning and ends at known points .

PROCEDURE :

1. Positions for stations ischoosed as close as possible to the objects to be located.

2. The stations is marked by peg/picket with the ground and should be visible each

other.

3. The chosen distance between point >30m and 100m .

4. The prismatic compass is used to assume the baseline.

5. Observations of angle and distance could be clockwise from baseline.

6. A total station/theodeliteis set up on the face left at station 2, centre it over the

ground station mark and is level accurately with levelling screws.

7. Sight the telescope towards station 1, clamp the upper and lower plates and sight

the signal at 1 accurately. Set up the angle and target distance 2-1.

8. Then the upper plate is unclamp , swing the TS/theodolite clockwise and sight the

signal at 3. Accurate bisection of the signal is made by using upper tangent screw

only. Read the angle and distance 2-3

9. Step 7-8 is repeated to get the face right at station 2-1 and 2-3

10. Both of the angle is read and find the average reading.

11. The TS/theodolite is shifted to the next traverse stations in turn and the step 6-10

is repeated at every traverse station in the same sequential order.

12. The areas , accuracy ratio is calculated and correction of traversing is applied .


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(II) DETAILING MEASUREMENT

Detailing measurement is a important method to preparation of topographic maps which

require both elevations and horizontal distances.

THEORY :

As height differences between staff positions and instrument increase, it will become

impossible to use the horizontal line of sight which so far has only been considered.

Figure 9 : Traverse Tachimetry

1. On one end of the designated line, set up and level the instrument at point 2.

2. Direct the STAFman to hold vertically a levelling STAF at the other end of the line

(point 1) and take a BACKSIGHT on the staf. Set the bearing 2 to 1 based oncompass bearing.

3. Observe through the telescope the apparent location of the stadia hairs on the staf and

record the upper, middle and lower stadia hair readings.

4. Read the vertical angle and record this quality. Indicate its corresponding sign. An

angle of elevation is a plus (+) angle and an angle of depression is a minus (-) angle.

5. Using the stadia staf, measure the actual height of the instrument above the occupied

point and record this as the Hi.


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6. Then, place the staf at point 3, observe bearing (H), vertical angle (V) and stadia

readings.

7. Move the instrument at point 3 and repeat step 2 to 6 (but bearing to setting is refer to

bearing 2 to 3). Follow this step until instrument move at point 1.

Figure 10 : Incline sight vertical staff method diagram

Inclined Sights Formulae

HD = Ks (cos )

VD = Ks sin2

Where : HD = Horizontal distance

VD = Vertical distance

K = Stadia interval factor

s = Stadia intercept (upper rdg lower rdg)

c = Distance from center of instrument up to principal focus = 0 ( for internal focusing

telescope )


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Figure11 : Line of traverse

1. The instrument is set up at station 2. Assume station 1 as a Reference station.

2. Compass at station 1 is set up and the reference bearing is obtained.

3. Then the theodolite is set up at the same point (stn 2)

4. The reference bearing from compass is setting at the theodolite. (from 2 to 1)

5. The rod staff is placed at point 1. The vertical angles is measured twice for one single

observation.

6. State the first reading of vertical angle as and taken cross-hair stadia

readings(middle).

7. Then the stadia intercept is measured by opening the second verticle angle .

8. The verticle angle can indicate the maximum intercept. The staff and verticle anglevalue reading is taken.

9. The staf is transfered at point 3. The bearing is opened from point 2 to 3.

10. The procedure 6-8 is repeated.

Figure 12 : Tangential method diagram


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5.0 DATA

a. Horizontal Sight

b.

Inclined Sight


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Stnocc Stnobs Horizontal

Circle

Vertical

Circle

Stadia

Readings HD VD2 1 2834920 a=854520

=740100

a=4.945

b=2.340

3 2044800 a=882920

b=724440

a=4.865

b=1.725

3 2 244800 a=934740

b=715000

a=4.935

b=0.620

1 3303920 a=904940

b=764300

a=4.940

b=1.180

1 3 1503920 a=893840

b=763440

a=4.955

b=1.505

2 1034920 a=911000

b=733640

a=4.960

b=1.115


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6.0 DATA ANALYSIS

a. Horizontal Sight

b.

Inclined Sight


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Stnocc Stnobs Horizontal

Circle

Vertical

Circle

Stadia

Readings HD VD2 1 2834920 a=854520

=740100

a=4.945

b=2.340

12.275 3.516

3 2044800 a=882920

b=724440

a=4.865

b=1.725

11.047 3.431

3 2 244800 a=934740

b=715000

a=4.935

b=0.620

16.481 5.408

1 3303920 a=904940

b=764300

a=4.940

b=1.180

16.965 4.007

1 3 1503920 a=893840

b=763440

a=4.955

b=1.505

14.843 3.542

2 1034920 a=911000

b=733640

a=4.960

b=1.115

14.046 4.131

7.0 CONCLUSION

Our field work was carried out successfully . We work in a group when doing this field work.

Based on the result that we have collected, we know to measure of horizontal of sight (based

on stadia principle), tachymetry by vertical staff fixed stadia (inclined sights), and tachymetry

by tangential (tangential system) by using vertical staff formulae, normal/incline staff

formulae and tangent formulae. From the result that we have gained from the fieldwork ,we

managed to corrected the bearing. But we really enjoyed when doing this fieldwork.

tachimetry.docx

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