Adjustment of a close traverse

Adjustment of a Closed Traverse

In traverse surveying, a closed traverse forms a closed polygon where the survey starts and ends at the same point or at known control points. Due to errors in measurement, the traverse may not close perfectly. Therefore, adjustment is required to correct these errors. In ITI Draughtsman Civil, understanding the adjustment of a closed traverse is essential for accurate mapping and engineering work.

1. Definition

Adjustment of a closed traverse is the process of distributing the errors in measured angles and distances so that the traverse forms a perfect closed figure.

2. Types of Errors in Traverse

• Angular Error: Error in measurement of angles.
• Linear Error: Error in measurement of distances.

3. Angular Adjustment

The sum of interior angles of a closed traverse should satisfy:

• Sum of interior angles = (2n – 4) × 90°

Where n is the number of sides.

Procedure

1. Calculate the theoretical sum of angles.
2. Find the difference between measured and theoretical sum.
3. Distribute the error equally among all angles.

4. Linear Adjustment (Closing Error)

After angular adjustment, the closing error in linear measurements is calculated.

Closing Error

• It is the difference between the starting and ending point.

Relative Precision

• Ratio of total traverse length to closing error.

5. Methods of Adjustment

(a) Bowditch’s Method (Compass Rule)

• Assumes errors are proportional to lengths of lines.
• Correction is distributed based on line lengths.
• Suitable when angles and distances are of equal accuracy.

(b) Transit Rule

• Corrections are proportional to latitudes and departures.
• Used when angular measurements are more accurate.

6. Steps in Traverse Adjustment

1. Check and adjust angular measurements.
2. Calculate bearings of all lines.
3. Compute latitudes and departures.
4. Determine closing error.
5. Apply corrections using suitable method.
6. Obtain corrected coordinates.

7. Importance of Adjustment

• Ensures accuracy in survey results.
• Helps in correct plotting of traverse.
• Reduces errors in construction layout.

Precautions

• Take accurate field measurements.
• Check calculations carefully.
• Use appropriate method for adjustment.

Role of Draughtsman Civil

A Draughtsman Civil uses adjusted traverse data to prepare accurate maps and layouts. Proper adjustment ensures correct representation of the survey area.

Conclusion

Adjustment of a closed traverse is essential to correct errors and ensure accurate survey results. Methods like Bowditch’s rule and transit rule are commonly used.

For ITI Draughtsman Civil students, understanding this process is important for reliable surveying and successful engineering projects.