V3 - Traverse Survey Report

KNS 1461 Civil Engineering Laboratory 2 Faculty of Engineering Universiti Malaysia Sarawak

_____________________________________________________________________ TITLE : V3 – Traverse Survey

INTRODUCTION: A traverse survey is one in which the framework consists of a series of connected lines, the lengths and direction of which are measured with the help of tape or chain and an angle measuring instrument. In other words, traverse survey consists of an interconnected series of lines, running between a series of points on the ground called traverse stations. A traverse survey is performed to measure both the distances between the stations and the angle between the lines. Traverses have been used for local horizontal control over relatively small area or for precise control over relatively large area.

When the lines from a circuit which ends at the starting point, the survey is termed a closed traverse, if the circuit does not close, the traverse os known as open one.The closed traverse is suitable for wide areas and for locating the boundaries of the lakes,wood etc. ,where an open traverse is carried out in the of long strips of country as in the case of canal, road , railway etc. In total station traversing, total station is used for measurement of angles or tape or chain, preferable, steel tape is used for linear measurement .This method is applied for accurate and precise survey but for this fieldwork, we have to estimate our own distance by using pegs.

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_____________________________________________________________________ THEORY: METHOD OF TRAVERSING The method of measuring the angle and bearing of a traverse may be divided into classes: a) Those in which the angle at different stations are measured directly and the bearing subsequently calculated from the measured angles and the given bearing of an initial line b) By direct observation of bearing of different survey lines by a total station.

A) Total Station Traversing by Direct Observation of Angle:- In this method, horizontal angles measured at different stations may be either, i. Included Angle, or ii. Defection Angle 1) Traversing by the method of included angles:In a closed traverse included angles can be measured by running a traverse in clockwise or counterclockwise direction. The common practice is to run a closed traverse in counterclockwise direction, but it is well to adhere to a regular of routine of measuring angles. Generally interior angles are obtained it the traverse is run anticlockwise and exterior ones when it is run clockwise as shown in the figure 3.1.

Figure 3.1

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_____________________________________________________________________ The angle may be measured by the repetition method and the observation should be taken with both the faces and also by reading both the verniers. Then averaging the value of each angle should be calculated. It will ensure desired degree of accuracy and removal of most of the instrumental errors.

2) Traversing by the method of deflection angle:This method of traversing is more suitable in surveys for railway, roads, pipeline etc. in which a series of traverse lines may make small deflection angles with each other. In measuring deflection angles having observed the bearing at the starting station ‘L’ Set the theodolite at each of station such as M,N,O,Q. Bisect the back stations using lower clamp and its tangent screw. The vernier may be set to zero or the initial reading may be taken. The theodolite is transited and the forward station is bisected with upper clamp screw and the tangent screw. The verniers are again read, the difference between the first set of reading and the second gives the angle of defection. The measurement is either right or left handed and this direction must be most carefully noted in the field book. Chaining is done in the usual manner.

Figure 3.2 Deflection Angle Method

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_____________________________________________________________________ INTRODUCTION TO THE EQUIPMENT Total station combines an EDM instrument, an electronic digital theodolite and a computer in one unit. These devices automatically measure horizontal and vertical angels, as well as distances and transmit the results in real time to a built-in computer. The data can all be stored within the instrument or in an automatic data collector, thereby eliminating manual recording. If the instrument is oriented in direction and the coordinates of the occupied station are input to the system, the coordinates of any point sighted can be immediately obtained. Total station instruments can accomplish all surveying tasks including topographic, hydrographic, construction surveys and cadastral mush more efficiently than transits and theodolites. In addition the can also measure distances accurately and quickly. These devices can automatically measure horizontal and vertical angles, as well as slope distance from a single setup. From the data they can instantaneously compute horizontal and vertical distance compoenents, elevations and coordinates of points sighted and display the results on a liquid crystal display (LCD). All total stations have the same common feature, which are as follows: 

Horizontal tangent screw o The clamp ensures that when engaged the horizontal circle is fixed.



Horizontal motion clamp o The slow motion screw allow for the movement of the instrument around the horizontal axis.



Optical plummet telescope o The optical plummet allows the instrument to be precisely centered over the station. The line of sight through the optical plummet is exactly the same as the vertical axis of the total station

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_____________________________________________________________________ METHOD OF EXECUTING THE FIELDWORK: Temporary adjustment of total station should be made at every instrument setting and preparatory observation with instrument. The temporary adjustments include: i.

Setting up of the instrument Assuming that the total station is to be erected over a ground mark which is a peg driven into the ground. A nail driven into the top of the peg defines the exact position for centering, which may referred to as station X. The equipment must be centred all the time over the station mark X by using a plum bob by adjusting legs. It is also important to adjust the small circular bubble so that it is centred by using eye judgement.

ii.

Levelling up After having centred and approximately levelled the instrument, accurate leveling is done by adjusting the foot screws to move the optical plummet cross-hair with the reference to the plate level. It is important in order to make the vertical axis exactly vertical.

iii.

Eliminating Parallax Parallax is a condition happen when the image formed by the objective is not in the plane of the cross-hairs. Parallax should be eliminated in order to have accurate sighting. There are two ways to overcome or eliminate the parallax. There are by accurately focusing the cross-hairs against a light background and focusing the instrument on a distant target or by focusing the eye-piece for distinct vision of the cross hairs.

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_____________________________________________________________________ OBJECTIVE : To make a traverse survey, reduce the field data and plot the results graphically

APPARATUS / EQUIPMENT: 

Total station



Tripods



Prism



Nail



Hammer



Wooden Peg

Tripods Total Station

Prism

Hammer

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_____________________________________________________________________ PROCEDURE :

1. Surrounding of Siar Beach Resort, Lundu was chosen as a scope of study or proposed site. 2. Three control points (CP) were established at the proposed site. (peg A, peg B and peg C). 3. The total station was plumbed over peg 2 and accurately leveled. Prisms were plumbed over peg 1 and 3. 4. Peg 1 were sighted on face left with theodolite set to the required horizontal angle. The reading was entered in the field book. 5. Peg 3 were sighted and the horizontal angle was taken. 6. The instrument was set to face right (by transiting the telescope) and peg 1 was sighted again. 7.

Peg 3 was sighted and the reading was taken.

8. Distance was measured by collimating the center of prism at peg 1. The reading was taken and entered in the field book. Distance between peg 2 and 3 also done with the same technique. 9. The total station was moved to peg 3. Prisms were plumbed over peg 2 and 4. Peg 2 was sighted on face left with theodolite set to the reading taken from step 7 above. 10. Peg 2 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. 11. Distance was measured the same way for both peg by repeating step 8. 12. Step 9-11 was repeated on peg 3 until the total station back to peg 1. All readings were observed and recorded.

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_____________________________________________________________________ RESULT: *Please refer to form B and form C attached to this report

SAMPLE OF CALCULATION: Misclosure = Last of Mean – Datum = 124°29’45” – 304°30’00” – 180°30’00” = – 0°0’15” Since the last mean is smaller than the bearing of datum, thus the correction is 0°0’15”. Correction: Station 1 = (1 x 0°0’15”) /10 = 1.5” Station 2 = (2 x 0°0’15”)/10 = 3.0” Station 3 = (3 x 0°0’15”)/10 = 4.5” Station 4 = (4 x 0°0’15”) /10 = 6.0” Station 5 = (5 x 0°0’15”)/10 = 7.5” Station 6 = (6 x 0°0’15”)/10 = 9.0” Station 7 = (7 x 0°0’15”) /10 = 10.5” Station 8 = (8 x 0°0’15”)/10 = 12.0” Station 9 = (9 x 0°0’15”)/10 = 13.5” Station 10 = (10 x 0°0’15”) /10 = 15.0”

Reduce HCR = Mean – Correction 190°30’10” + 1.5” = 190°30’12”

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_____________________________________________________________________ DIAGRAM: *Please refer to A3 paper attached to this report

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_____________________________________________________________________ Included Angles: Line

Reduce HCR

Calculation

Interior Angle

2-1

304°30’00”

304°30’00” – 190°30’12”

113°59’48”

2-3

190°30’12”

3-2

10°30’12”

360° + 10°30’12” –

179°40’22”

3-4

190°49’50”

190°49’50”

4-3

10°49’50”

360° + 10°49’50” –

4-5

292°13’50”

292°13’50”

5-4

112°13’50”

360° + 112°13’50” –

5-6

296°59’20”

296°59’20”

6-5

116°59’20”

116°59’20” – 65°14’50”

51°44’30”

6-7

65°14’50”

7-6

245°14’50”

245°14’50” – 55°51’03”

189°23’47”

7-8

55°51’03”

8-7

235°51’03”

235°51’03” – 87°24’43”

148°26’20”

8-9

87°24’43”

9-8

267°24’43”

267°24’43” – 116°2’44”

151°21’59”

9-10

116°2’44”

10-9

296°2’44”

296°2’44” – 20°59’56”

275°02’48”

10-1

20°59’56”

1-10

200°59’56”

200°59’56” – 124°30’00”

76°29’56”

1-2

124°30’00” Total (2n – 4) x 90°

1440°00’00”

78°36’00”

175°14’30”

Total included angle obtained = Total included angel in a triangle (proven)

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_____________________________________________________________________

Where

and

Where

Where

*Please refer to the appendix for the sample of calculation on this part*

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_____________________________________________________________________ DISCUSSION : From the data table on previous page, the last mean obtained is not the same as the bearing of the face right, which are 124°29’15” and 304°30’00” respectively. Since the bearing of the face left is normally taken as datum, the bearing of the face right is corrected as 124°30’00”. The misclosure of the traverse can be obtained from the following formula: Misclosure = Last of mean – Datum In this fieldwork, we have calculated and found out that the misclosure for this traverse is 0°0’15”. Since the last mean obtained is smaller than the bearing of the datum, the misclosure is now become positive. This shows that the last mean has to be added by certain degree of correction in order to get the same bearing as datum. In order to obtain the correction for each station, it can be obtained by multiplying the setup number with the value of misclosure and divided by the total number of station. This can be proven by following formula :

Errors are said to be unavoidable. Hence, correction is needed to corrected any error that commonly caused by the instruments. Furthermore, the correction has to be done due to misclosure of the traverse. If we refer to the recorded mean and the datum, it does not meet at the same bearing After all the bearings have been corrected, those bearing will be used to draw or sketch the area and diagram of the traverse. From this diagram, the included angles are calculated based on the bearings of the lines of the traverse and also be referring to the drawn diagram. From the diagram have been drawn, the shape of the traverse is triangle. The total included angle of any polygon is calculated based on the formula: Total included angle = (2n – 4)90°

where n is the number of side, which is refers to number of station for this case

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_____________________________________________________________________ For this polygon, the total included angle is 1440°00’00”, obtained from the above formula. By adding all the include angle of our traverse based on the bearings of the lines of traverse and the diagram, both of them resulting a value of 1440°00’00”. This shows that our included angle are valid and this prove that our traverse has been corrected correctly. Then, we are executing the linear measurement and partial coordinates. This can be done by summing the positive and negative partial coordinates for both northing and easting (latitude N and departure E). The algebraic sum should be zero in both cases as the traverse finished at the same point at which it started. For this fieldwork, we are using Compass (Bowditch’s) Method as it is one of the easiest method in order to determine the partial coordinates. We calculated both latitude and departure based on the following formula:

Where

and

Where

we obtained 0.111 and 0.037 for our latitude and departure. This misclosure can be obtained by summing up all the positive and negative partial coordinates for both northing and easting (latitude N and departure E).The accuracy of the usual traverse with a 1-minute transit is about 1:30000(at 1st survey order) Therefore this value is still acceptable. The correction was made for both latitude and departure by using a given formula (Compass rule) :

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_____________________________________________________________________

Where

By using this formula, we are able to adjust the latitudes and departures to ensure that the sums of latitudes and departures equal to zero. For this fieldwork, our latitude is set at 1°44’54.450” N while our departure is 109°52’35.868” E. After doing all the calculation, we found out that the latitude and departure back to 1°44’54.450” N and 109°52’35.868” E respectively. Hence, this shows that our calculation that we made is correct.

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_____________________________________________________________________ Question 1 Prepare the survey plan for your control traverse.

In order to prepare our survey plan, we are using a method called Radiation Method:- In this method the rays are drawn from the instrument station to the point to be located, then the distances are measured from the instruments station to the point and the position of the each point is plotted on the sheet using a suitable scale. The method is most suited for surveying small areas which can be controlled by single setting. It can also be used in combination with other method. This method can be applied for locating distant points if the distances are obtained tacheometrically with the help of the telescope alidade.

To contruct the survey plan, we use an A3 paper, a standard scale ruler and a compass. For this fieldwork, we are using a scale of 1:500. This is because we found out that this scale is the most suitable scale for the size of our traverse to the A3 paper. If we are to choose either 1:200 or 1:1000, it may be too big or too small for our A3 paper. If it is too big, we may no able to write any information on the A3 paper (for example, the Reduce level, bearing, etc) or even worst, the drawing is not fit on the A3 paper. If it is too small, it may be hard to draw the traverse accurately (the distance between two points) as the scale is too small.

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_____________________________________________________________________ Question 2 Discuss the sources of error that may arise when measuring traverse angles.

Error is said as unavoidable while doing total station fieldwork. This error can be calculated as follow: Misclosure = Last of mean – Datum At the first attempt of this fieldwork, we failed to get the accuracy of 2nd class order. This is because we obtained a misclosure of 0°07’35” which is more than the limit misclosure of 2nd class order which is 0°02’30”. This is due to unavoidable circumstance as the total station that we used is broken (there’s a problem arise when we’re trying to calibrate the optical plummet telescope). Hence due to this, we have to re-do this fieldwork all over again. On the second attempt, we changed the total station and after executed this fieldwork, we calculated and found out that the misclosure for this traverse is 0°0’15”. After that, correction is made, which have been shown in sample of calculation section. There are several factors contributing to this error that may arise during measuring traverse angle, which are: 

Inaccurate centering of the total station or signal



Non-verticality of the signal



Parallax not eliminated or improper focusing of telescope



Lateral refraction, wind and atmospheric effects



Inaccurate bisection of the signal



Total station not level and not in adjustment



Incorrect use of the total station



Mistakes in reading and booking

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_____________________________________________________________________ During executing this fieldwork, we identified that the following factors are mainly contributing to this error, which are: 

Inaccurate centering of the total station or signal o The centering may not inaccurate, but we did our best to get it as accurate as possible.



Total station may not level and not in adjustment o During the experiment, we have to level and centering the total station at the same time. Since the centering may not inaccurate, there’s a possibility that total station may not level but as far as our concerned it is leveled and centered.



Parallax not eliminated or improper focusing of telescope o There may be parallax error exist while focusing the telescope to the prism.



During our experiment was commenced, the weather is rainy. This may affect our result as the soil is damp and the peg may move a little bit to right or left.



Some of the pegs are missing as it may get hit by the car and we have to estimate the last point where the pegs are located.



Prism may not level and not in adjustment o During the experiment, we have to level and centering the prism at the same time. Since the centering may not accurate, there’s a possibility that prism may not level though as far as our concerned it is leveled and centered.

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_____________________________________________________________________ CONCLUSION: From the fieldwork executed, we have come up with the results obtained from the fieldwork executed using the method of traversing for a closed traverse. Although there’s misclosure, the correction had been made to this data. It is shown that these values calculated are valid since they converge with the theoretical value given. For example, the total included angle in a polygon and the total included angle of our polygon is 1440°00’00”. This shows that our included angle are valid and this prove that our traverse has been corrected correctly. For our booking on linear measurement and partial coordinates, we obtained a misclosure of 0.111 for our latitude and 0.037 for our departure. Since the accuracy of the usual traverse with a 1minute transit is about 1:30000(at 1st survey order), therefore this value is still acceptable. Errors are commonly found in traverse survey. By taking several precautions (make sure that total station leveled and adjusted, accurately centering of the total station or signal, no parallax error by using proper focusing of telescope) should be taken in order to reduce the error.

RECOMMENDATIONS The execution of the fieldwork should be done carefully. The errors that we get from conducting this experiment are caused by local attraction, instrumental and human errors. Since the surrounding area has metal materials and also magnetic field due to sub-station near to scope of study, these things may cause errors in our readings by mean of local attraction. The setting up of instrument could also contribute errors in our readings. Local attraction cannot be minimized as it is exists as it is in any environment. However, instrumental errors can be eliminated or minimized by carefully manipulation of instrument and by limiting the length of sight. This can be done by: 

Make sure that there’s no error or broken on the instruments used



Make sure that total station leveled and adjusted



Accurately centering of the total station or signal



No parallax error by using proper focusing of telescope

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_____________________________________________________________________ Human errors can be minimized by doing the fieldwork carefully and with intention to get the most accurate results possible.

REFERENCES: Books 

2009, Hasbullah M.A., Openg I., Simplified Land Surveying, Arah Publichations



2005, Dr. Punmia B.C., Jain A.K., Jain A.K, Surveying Vol. 1, Laxmi Publications (P) Ltd

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_____________________________________________________________________

APPENDICES

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V3 - Traverse Survey Report

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