Compass survey Topics covered Compass Surveying Meridian Bearing
Compass survey
Topics covered – Compass Surveying Meridian & Bearing Ø - true, magnetic and arbitrary Traverse - closed, open. System of bearing - whole circle bearing, Reduced bearing, fore bearing, and back bearing, conversion from one system to another. Angles from the bearing and vice versa. Prismatic, Surveyor, Silva and Bronton (introduction) compass Local attraction with numerical problems. Plotting of compass survey (Parallel meridian method in detail). 2
Definition Limitation of chain surveying Angle or direction measurement must Azimuth, Bearing, interior angle, exterior angle, deflection angle α ß B B θ A θ 1800 + θ-ß A B α γ θ ß E Φ C B D D Φ E ß C A γ C 250 R C 220 L A 3
Compass surveying Compass used for measurement of direction of lines Precision obtained from compass is very limited Used for preliminary surveys, rough surveying 4
5. 1 Meridian, Bearing & Azimuths Meridian: some reference direction based on which direction of line is measured True meridian ( Constant) Magnetic meridian ( Changing) Arbitrary meridian Ø Ø Ø Bearing: Horizontal angle between the meridian and one of the extremities of line Ø Ø Ø True bearing Magnetic bearing Arbitrary bearing Source: www. cyberphysics. pwp. blueyonder. co. uk 5
Contd… 5. 1 Meridian, Bearing & Azimuths True meridian Ø Ø Line passing through geographic north and south pole and observer’s position Position is fixed Established by astronomical Observer’s position observations Used for large extent and accurate survey (land boundary) Geographic north pole 6
Contd… 5. 1 Meridian, Bearing & Azimuths Magnetic meridian Ø Ø Ø Line passing through the direction shown by freely suspended magnetic needle Affected by many things i. e. magnetic substances Position varies with time (why? not found yet) Assumed meridian Ø Ø Ø Line passing through the direction towards some permanent point of reference Used for survey of limited extent Disadvantage v Meridian can’t be re-established if points lost. 7
Reduced bearing N Either from north or south either clockwise or anticlockwise as per convenience Value doesn’t exceed 900 Denoted as N ΦE or S Φ W The system of measuring this bearing is known as Reduced Bearing System (RB System) W B NΦE E A S N W B E A SΦW S 8
Whole circle bearing (Azimuth) Always clockwise either from north or south end Mostly from north end Value varies from 00 – 3600 The system of measuring this bearing is known as Whole Circle Bearing System (WCB System) N B 450 W E A S N B 3000 W A E S 9
5. 2 Conversion from one system to other N Conversion of W. C. B. into R. B. D W θ A Φ E o ß α C B S Line W. C. B. between Rule for R. B. Quadrants OA OB OC OD 00 and 900 and 1800 and 2700 and 3600 R. B. = W. C. B. = θ R. B. = 1800 – W. C. B. = 1800 – Φ R. B. = W. C. B. – 1800 = α – 1800 R. B. = 3600 - W. C. B. = 3600 - ß. NθE SΦE SαE SßE Unit 5: Compass traversing & Traverse computation 10
Contd… 5. 2 Conversion from one system to other N D ß W θ A E o Φ Conversion of R. B. into W. C. B. α B C S Line R. B. Rule for W. C. B. between OA OB OC OD NθE SΦE SαE SßE W. C. B. = R. B. W. C. B. = 1800 – R. B. W. C. B. = 1800 + R. B. W. C. B. = 3600 - R. B. 00 and 900 and 1800 and 2700 and 3600 11
5. 2 Fore & back bearing Each survey line has F. B. & B. B. In case of line AB, Ø Ø F. B. is the bearing from A to B B. B. is the bearing from B to A Relationship between F. B. & B. B. in W. C. B. B. B. = F. B. ± 1800 Use + sign if F. B. < 1800 + θ B & θ use – sign if F. B. >1 1800 A Unit 5: Compass traversing & Traverse computation C ß - 1800 D 12 ß
Contd… 5. 2 Fore & back bearing Relationship between F. B. & B. B. in R. B. system B. B. =F. B. Magnitude is same just the sign changes i. e. cardinal points changes to opposite. B NΦE SΦW A D SßE NßW C 13
5. 2 Calculation of angles from bearing and vice versa In W. C. B. system ( Angle from bearing) Ø Ø Ø Easy & no mistake when diagram is drawn Use of relationship between F. B. & B. B. Knowledge of basic geometry B ß B Θ-1800 -ß ß θ A 1800 + θ-ß θ C A Unit 5: Compass traversing & Traverse computation C 14
5. 2 Calculation of angles from bearing Contd… and vice versa In R. B. system (Angle from Bearing) Ø Ø Easy & no mistake when diagram is drawn Knowledge of basic geometry B B NθE SθW SßE 1800 -(θ+ß) A A SßE Θ+ß C C 15
5. 2 Calculation of bearing from angle Normally in traverse, included angles are measured if that has to be plotted by co-ordinate methods, we need to know the bearing of line Ø Ø Ø Bearing of one line must be measured Play with the basic geometry Diagram is your good friend always ? ? Unit 5: Compass traversing & Traverse computation Ø ? ? 16
Contd… 5. 2 Calculation of bearing from angle =? Bearing of line AB = θ 1 Back Bearing of line AB = 1800 + θ 1 = 3600 – BB of line AB = 3600 -(1800 + θ 1) is also = alternate angle of (1800 – θ 1) = (1800 – θ 1) Fore Bearing of line BC =θ 2 = α – = α -[3600 –(1800 + θ 1) ] = α+ θ 1 - 1800 17
Contd… 5. 2 Calculation of bearing from angle =? Bearing of line BC = θ 2 Back Bearing of line BC = 1800 + θ 2 = 3600 – BB of line BC = 3600 -(1800 + θ 2) Fore Bearing of line CD = θ 3 = ß – = ß -[3600 –(1800 + θ 2) ] = ß+ θ 2 - 1800 Unit 5: Compass traversing & Traverse computation 18
Contd… 5. 2 Calculation of bearing from angle Ø ? Bearing of line CD= θ 3 ? = 1800 + θ 3 Back Bearing of line CD = 3600 – BB of line CD = 3600 -(1800 + θ 3) Fore Bearing of line DE = θ 4 = γ – = γ -[3600 –(1800 + θ 3) ] = γ+ θ 3 - 1800 19
Contd… 5. 2 Calculation of bearing from angle Ø =? Bearing of line DE= θ 4 Back Bearing of line DE = 1800 + θ 4 Fore Bearing of line EF = θ 5 = BB of line DE + Ø = 1800 + θ 4 + Ø Unit 5: Compass traversing & Traverse computation 20
5. 2 Numerical on angle & bearing What would be the bearing of line FG if the following angles and bearing of line AB were observed as follows: (Angles were observed in clockwise direction in traverse) ABC = 1240 15’ BCD = 1560 30’ CDE = 1020 00’ DEF = 950 15’ EFG = 2150 45’ Bearing of line AB = 2410 30’ 21
5. 2 Numerical on angle & bearing ABC = 1240 15’ BCD = 1560 30’ CDE = 1020 00’ DEF = 950 15’ EFG = 2150 45’ Bearing of line AB = 2410 30’ G A 2410 30’ A 2150 1240 15’ G ? 45’ 1240 15’ B F 2150 45’ 950 15’ B E F 1560 30’ C 1560 C 30’ 1020 950 15’ 00’ 1020 00’ E D D Unit 5: Compass traversing & Traverse computation 22
5. 2 Numerical on angle & bearing A 2410 30’ FB of line BC = (2410 30’- 1800) + 1240 15’ = 1850 45’ 1240 15’ B 1850 45’ B C 1560 30’ C D FB of line CD = (1850 45’- 1800) + 1560 30’ = 1620 15’ 23
5. 2 Numerical on angle & bearing 1620 15’ FB of line DE =1020 00’ - (1800 - 1620 15’) = 840 15’ C F 1020 00’ 950 15’ E 840 15’ D E D FB of line EF = (840 15’+1800) + 950 15’ = 3590 30’ Unit 5: Compass traversing & Traverse computation 24
5. 2 Numerical on angle & bearing FB of line FG =2150 45’ - {1800+(BB of line EF)} FB of line FG =2150 45’ - {(1800 +(00 30’)} = 350 15’ 2410 30’ A G 1240 15’ G B 2150 45’ F 1560 30’ F C 950 15’ 1020 00’ 3590 E 30’ E D 25
Contd… 5. 2 Numerical on angle & bearing From the given data, compute the missing bearings of lines in closed traverse ABCD. B Bearing of line AB = ? Bearing of line BC = ? Bearing of line CD = N 270 50’E Bearing of line AB = ? A = 810 16’ B= 360 42’ D = 2260 31’ A D C Unit 5: Compass traversing & Traverse computation 26
Contd… 5. 2 Numerical on angle & bearing For the figure shown, compute the following. Ø Ø Ø The deflection angle at B The bearing of CD The north azimuth of DE The interior angle at F B 0 N 41 A S 5 50 E 7’ 26 ’E 0 C 790 16’ N 120 58’W D S 120 47’E F S 860 48’W E 27
Contd… 5. 2 Numerical on angle & bearing Deflection Angle at B = 1800 - (410 07’+550 26’) = 830 27’ R B 0 N 41 A 0 S 5 50 E 7’ Bearing of line CD = 1800 - (790 16’+550 26’) 26 ’E C = S 450 18’ W 790 16’ = 167 0 13’ D Interior Angle E = 1800 – (120 47’ + 860 48’) S 1 N 120 58’W North Azimuth of line DE = 1800 - 120 47’ 0 2 = 80 0 25’ ’E 47 F S 860 48’W E Interior Angle F = (120 58’ + 860 48’) = 99 0 46’ Unit 5: Compass traversing & Traverse computation 28
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