Tacheometry Report

Introduction: Tacheometric survey (Tacheometry) is a branch of surveying in which horizontal and vertical distance of points are obtained by optical measurement avoiding ordinary and slower process of measurement tape. Tacheometric surveys are usually performed to produce contour and details plans for further work, or to produce coordinates for area and volume calculations. Observation are usually performed from known survey stations, often established by traversing.

Objective: Produce the topographic and detail plan of the proposed area using surveying software.

Theory: Used a Total Station, able to read distance by reflecting off a prism. • The stadia procedure is used less and less often these days, more commonly geomatic engineers or civil engineers use a Total Station • This instrumentation has facilitated the development of this method of detail and contour surveying into a very slick operation. • It is now possible to produce plans of large areas that previously would have taken weeks, in a matter of days.

Where: D = Distance RL = Reduced Level HI = Height of Instrument HT = Height of Pole V = Vertical Elevation

Practice Equipments: No 1 2 3 4 5

Items Total Station Mini Prism Tape Pole Tripod

Quantity 1 2 1 2 1

Fieldwork Procedures:

Tachemetry or detail survey is a continuation of traversing and leveling wherein all the detail are observe from the traverse point with (x, y, h). •

All the traverse point had the reduced level from the leveling.

•

The leveling data of traverse point is referred.

1. All the details including topography and man-made features have observed.

2. The instrument was setup over the traverse (i.e. stn 4). The pole with mini prism was put at

the back sight (stn 1) and foresight (stn 3). 3. The temporary adjustment (leveling, centering) over the point was performed. 4. The height of instrument (IH) was measured and recorded. 5. The bearing for line 4-1 was set as datum. The distance of stn4-stn1 was measured and recorded. Used a final bearing from traverse sheet. 6. A pole was used as a target over the point. The pole height (HT) is measured and the reading

was recorded. 7. The horizontal bearing (HR), horizontal distance (HD) and vertical distance@height

difference (VD) for each observation was recorded. 8. All the features surrounding the stn4 were observed. We make sure the HT was measured and recorded for each observation.

9. The instrument was moved to the next station (i.e. stn2). The bearing for line 2-3 was set as a datum. The process was repeated and all the features from stn2 were observed. The IH at each station setup was measured. 10. Additional control point must be setup when it found missing or disturbed; or obstruction of the features from observed station.

Procedure: 1) leveling

BS

FS

2) set datum Pris

Used a final bearing from traverse sheet.

1

4 TS

3) record HR, HD and VD for each observation

4 Building

Data Analysis: Levelling ∑BS - ∑FS = 14.022 – 14.013 = 0.009 ∑RISE - ∑FALL= 2.152 – 2.143= 0.009 RL (LAST BM) - RL (START BM) = 4.917 – 4.908 = 0.009 ∑BS - ∑FS = ∑RISE - ∑FALL = RL (LAST BM) - RL (START BM)

Allowable closure = ± (20√0.284) mm = 10.66mm Correction = 0.009/10 = 0.0009mm

Tacheometry RL = RLA + HI ± V – HT RL = 3.712 + 1.54 – 0.604 – 1.525 = 3.398

Discussion 1.

Tachometry also has the same errors like we’ve done in traversing. There are four specific sources of errors needed to be emphasized in tachometry observations. They are staff readings and tilt of the pole or staff. Observer tends to make wrong observation when observing the staff reading, they might misread the staff marking scales and this brought to the crucial error along the booking process. Besides, the tilting of the staff rod can influence the accuracy of the height readings taken from the staff. When the staff is not truly vertical (90 ) or almost to it, the reading taken is incorrect and lead to the failure of tachometry process.

2.

Besides, the errors encountered during tachometry also can be derived from instrumental errors. They are those caused by the adjustment of the instruments used or faults in them. Any errors in these measurements have serious implications in the heights and distances measured with the instruments. To avoid such errors, the following points should be taken care of:

3.

a)

The tachometer should be in perfect adjustment for taking observation.

b)

The altitude bubble should be at the centre of its run while reading the vertical circle for angles. Any index error should be detected and eliminated or accounted for.

c)

The multiplying and additive constants of the instrument should be periodically checked to see that they indeed have the values that are being used.

e)

The stadia rod (staff) should be accurately divided into parts. The graduations should be uniform and free of errors. They should be marked bold for greater visibility from a large distance.

Others errors due to manipulation and sighting are inaccurate leveling of the instrument, inaccurate reading of horizontal line and vertical angles, poor focusing errors, inaccurate bisection of the target, inaccurate reading of the staff intercept and lastly due to errors in holding the staff.

4.

Errors in conducting tachometry survey also caused by natural causes. These include errors due to high winds. During high winds, it is difficult to keep the staff vertical and read it accurately. Works should be undertaken during hot mid-day period. In very hot conditions, the instrument should be protected with an umbrella to avoid errors due to the unequal expansion of different parts of instruments. Work may also be hampered by bad visibility due to strong sunlight and glare.

Recommendation 1. We can take more reading and calculate the average value so that we can get rid of the errors and get more accurate results. 2. The area of the traverse point should not be too big so that we need not set up new station and keep changing the points. 3. We can postpone our fieldwork if the weather is not suitable. Bad weather might affect our results.

Conclusion We have achieved the contour and topographic details around family chalet no 2. Thus, we can conclude that our fieldwork is success.

References: 1. Masiri Kaamin dan Abd. Sukor Sarif (2006). Kejuruteraan Geomatik 1. Monograf; Batu Pahat: Fakulti Kejuruteraan Awam dan Alam Sekitar, KUiTTHO. 2. note from Dr.Sc Mohd Efendi Daud