FW5-4E2 Report - TOPIC: COMPASS SURVEY - LOCAL ATTRACTION PDF

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TOPIC: COMPASS SURVEY - LOCAL ATTRACTION...

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FACULTY OF PROG./COURSE CODE : AGR242 COURSE : GENERAL FIELD MAINTENANCE TOPIC: COMPASS SURVEY - LOCAL ATTRACTION FIELDWORK NO. G. LEADER NAME MATRIC NO. GROUP (COURSE) NO. 1. 2. 3. 4. 5.

NAME

MATRIC NO.

CHECK LIST FOR REPORT SUBMISION & CONTENT 1. REPORT COVER – fill in all the blanks, print and submit 2. Introduction (summarise) 3. Objectives (summarise) 4. Learning outcomes (summarise) 5. Procedures 6. Propose Sketch Traverse & Bearings (during fieldwork) 7. Bookings of Survey Data using Local Attraction Method (during fieldwork) 8. Calculation of Local Attraction, Misclosure & Final Bearing 9. Plotting of Compass Traverse (actual final bearing with scale on A3) 10. Conclusions 11. Discussion and Recommendations 12. Appendixes: Others - Photographs, Tables & Sketches with captions

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INTRODUCTION A local attraction is a phenomenon in which the magnetic needle is consistently stopped from pointing towards the magnetic north at a location. The reason for this is that other magnetic objects in the vicinity, such as wires carrying electric current, railroads, and so on, affect these magnetic compasses. Due to local attraction, a large degree of error in compass surveying observations can occur, and these errors will be consistent across all bearings.

OBJECTIVES To give exposure to the students about the process of determining the position of an object both by angular and linear measurements by using a compass.

LEARNING OUTCOMES By the end of this FW session students should be able to: 1. Setup compass survey stations 2. Setup compass equipment on the survey station correctly 3. Take back bearing and fore bearing of the compass traverse 4. Carry out appropriate booking 5. Perform angle corrections using local attraction method 6. Perform distance corrections 7. Plot the compass traverse with a suitable scale

PROCEDURES 1. Choose an appropriate location for establishing compass stations (A, B, C, D and E). Each distance must be a minimum of 10 metres and a maximum of 25 metres.

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2. Draw the Local Attraction Method traverse. 3. Place the range poles at stations B and E and set up the compass at station A. 4. Check that the compass bubbles are centred. 5. Centered the compass on survey station A with the plum bob 6. Look at the ranging pole until the cross hairs line up with the station B ranging pole. 7. Take the bearing and record it as a forward bearing on the field sheet. 8. Look at the range pole and take the bearing as the rear bearing at station E. 9. Calculate the lengths between lines AB and AE. 10. Set up the compass at station B by moving it there. 11. Position the ranging pole between stations A and C. 12. Take the bearings of station A and station C by looking at the range pole. 13. Continue with the rest of the stations in the same procedure. 14. Using the Local Attraction Method, calculate the final bearing. 15. Plot a traverse plan.

PROPOSE SKETCH TRAVERSE & BEARINGS (DURING FIELDWORK)

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BOOKINGS OF SURVEY DATA USING LOCAL ATTRACTION METHOD (DURING FIELDWORK)

A. Bookings of Survey Data (Local AttractionMethod)

Stn. Line

A B

AB BA BC

C

CB CD

D

DC DE

E

ED EA

A

AE

Distanc e (m) 24

Bearing

24

339°

24

172°

24

352°

23

270°

23

90°

23

5°

23

185°

20

72°

20

252°

149°

Difference

190°

180°

180°

180°

180°

Local Attractio n 10

Corrected Bearing 159°

0

339°

0

172°

0

352°

0

270°

0

90°

0

5°

0

185°

0

72°

0

252°

New Differenc e 190

180°

180°

180°

180°

Misclosur e

Final Bearing

Remarks & distance

-10

149°

AB

0

339°

BA

0

172°

BC

0

352°

CB

0

270°

CD

0

90°

DC

0

5°

DE

0

185°

ED

0

72°

EA

252°

AE

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CONCLUSIONS The incidence of nearby enchantment may be detected via way of means of gazing the distinction among the fore and lower back bearings. If there may be no impact of nearby enchantment and different error, this distinction may be 180. So we are able to then finish that each stations are unfastened from nearby enchantment. For the special casethis method is implemented while there may be no such observations which has a distinction of 180˚ in fore and lower back bearings of a line. Then the bearings of least discrepancy is chosen in this type of manner that the distinction of them is closest to 180˚. The imply cost is acquired via way of means of including half of the correction to fore bearing cost and half to lower back bearing. Hence a cost which differs via way of means of 180˚ may be acquired. So from this corrected bearing cost different values may be measured.Compass surveying isn't always encouraged for regions wherein nearby attraction is suspected because of nearby attraction like metal structures, magnetic

DISCUSSION i.

How can local attractions be corrected? •

The determined bearings are corrected through applying correction to the stations tormented by the local attraction. For this, blunders at every of the station is observed after which beginning from an unaffected bearing, the bearings of the successive lines are adjusted through applying corrections to them.

ii.

What is the Principle of Compass Survey? •

The Principle of Compass Survey is Traversing which is includes a chain of related lines the magnetic bearing of the lines are measured through prismatic compass and the distance (lengths) of the are measured through chain. Such survey does now no longer require the formula of a community of triangle.

iii.

Which method is more accurate in plotting a compass survey?

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•

If the length and bearing of a line are known, its projection at the y-axis and x-axis can be calculated after which plotted. This approach is the maximum correct of all of the techniques of plotting due to the fact the usage of protractor is absolutely accomplished away and every factor is plotted unbiased of the others.

iv.

v.

How many types of a compass are used in surveying? •

Prismatic Compass

•

Surveyor’s Compass.

•

Level Compass

How many errors in compass survey? •

Instrumental errors

•

Personal errors

•

Natural errors

RECOMMENDATIONS There are the subsequent techniques of correcting the discovered bearings of the lines taken withinside the location stricken by the local attraction: (i) The mistakess because of local appeal being equal for every of the bear-ings discovered at an affected station, the included angle calculated from the bearings taken on the identical station could be correct, even though, the station is affected by the local attraction. Starting from the unaffected line and the usage of those included angles, the suitable bearings of the successive lines are calculated as already explained. ii)The discovered bearings are corrected through applying correction to the stations stricken by the local attraction. For this, mistakes at every of the station is located after which beginning from an unaffected bearing, the bearings of the successive lines are adjusted through applying corrections to them. For the compass surveying the chain surveying may be used whilst the place to be surveyed is comparatively small and fairness flat. But whilst the place is large, 8

undulated and crowded with many details, triangulationthat is the precept of chain survey is not possible. In such the place, the technique of traversing is use. Lastly, to keep away from nearby attraction, not anything manufactured from iron or metal which includes bunch of keys, iron-buttons etc. have to be carried with the aid of using the surveyor. The device have to not, as a long way as possible, be installation close to telegraph poles, rails, different metal systems and currents wearing wires etc.

REFERENCE 1. Reference from lecture given by Sir Redzuandi Abdul Rahim 2. Compass Surveying, Retrieved from http://www.gangainstitute.com/wpcontent/uploads/2019/10/SURVEYING-1-btech-3rd-sem.pdf

APPENDIXES

MEASURING TAPE

PEG

HAMMER

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RANGING POLE

TRIPOD AND PLUMBOB COMPASS

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