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### E4004 Survey Computations A

Bowditch Adjustment

Traverse Adjustment

- Bowditch Rule
- based on the assumption that angles (bearings) are observed to the same degree of precision that distances can be measured

Bowditch Rule from E0007

- Adjust the angular misclose
- calculate the misclose in position
- adjust according to the formula

length of the current line

= latitude of the current line

= departure of the current line

= sum of the traverse line lengths

Bowditch - New Method

- Adjust the angular misclose
- calculate the misclose in position
- consider the diagram
- AB’C’D’ is a traverse from A to D

C’

D’

B’

A

D

Bowditch - New Method

- But the traverse coordinates of D’ are not the same as D
- the misclose at D is D’D

C’

D’

B’

A

D

Bowditch - New Method

- Let the traverse line lengths be 1, 2 and 3 as shown

- The total length of traverse is 1+2+3=6

C’

3

D’

2

B’

1

A

D

Bowditch - New Method

- In order to adjust the traverse such that D’ and D are coincident D’ would have to be corrected by a Brg and Dist equal to D’D

C’

3

D’

2

B’

1

A

D

Bowditch - New Method

- according to Bowditch the correction at each intermediate point is proportional to the length of each separate traverse line over the total traverse length times the misclose

C’

3

D’

2

B’

1

A

D

Bowditch - New Method

- In this example the correction at D’ must be

of the total misclose

- Divide D’D into 6 parts

C’

3

D’

2

B’

1

A

D

Bowditch - New Method

- The correction at B’ must be in the same direction but for a length proportional to 1/6 of the total correction

C’

3

D’

2

B’

1

A

BAdj

D

Bowditch - New Method

- The correction at C’ must be in the same direction but for a length proportional to (1+2)/6 of the total correction

C’

3

D’

2

B’

1

CAdj

A

BAdj

D

Bowditch - New Method

- The adjusted bearings and distances would form the lines as shown

C’

3

D’

2

B’

1

CAdj

A

BAdj

D

Bowditch - New Method

- A close program can be used to calculate the adjusted bearings and distances and the adjusted coordinates

C’

3

D’

2

B’

1

CAdj

A

BAdj

D

Bowditch - New Method

- Consider the triangle AB’B

- Once the correction (D’D) is known both lines AB’ and B’B are known

- The line AB can be calculated by closure

C’

3

D’

2

B’

1

CAdj

A

BAdj

D

Bowditch - New Method

- From Badj draw a line parallel to B’C’

- The bearing and distance BAdjC” are the same as for B’C’

- The line C”Cadj is the correction relevant to this line i.e. 2/6 Corr

C’

3

D’

2

C”

B’

1

CAdj

A

BAdj

D

Bowditch - New Method

- Close the triangle BAdjC”Cadj and the adjusted bearing and distance BAdjCAdj is found

C’

3

D’

2

B’

1

CAdj

A

BAdj

D

Bowditch - New Method

- Similarly, draw a line parallel to C’D’ from CAdj

- The line D”Dadj is the correction relevant to this line i.e. 3/6 Corr

C’

3

D’

2

C”

B’

1

CAdj

A

BAdj

D”

D

Bowditch - New Method

- Close the triangle CAdjD”Dadj and the adjusted bearing and distance CAdjDAdj is found

C’

3

D’

2

B’

1

CAdj

A

BAdj

D

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