Methods of Adjusting the Traverse
Traverse adjustment is an important surveying process used to distribute closing errors among traverse lines in order to achieve accurate coordinates and balanced survey computations.
Arbitrary Method
Corrections are applied based on surveyor judgment for small and less precise surveys.
Bowditch’s Rule
Corrections are distributed proportional to the length of traverse lines.
Graphical Method
Traverse error is adjusted graphically using scaled plotting techniques.
Transit Rule
Corrections are proportional to latitude and departure values of lines.
Axis Method
Corrections are distributed with respect to a selected reference axis.
Introduction
During traverse surveying, measurement errors are unavoidable due to instrumental, observational, and environmental factors. As a result, the plotted traverse may not close perfectly. Traverse adjustment methods are therefore used to distribute these errors systematically and obtain corrected coordinates.
Important Note: Traverse adjustment ensures that the sum of corrected latitudes and departures becomes zero for a closed traverse.
Arbitrary Method
The Arbitrary Method is the simplest method of traverse adjustment. In this method, corrections are distributed according to the surveyor’s judgment without following any fixed mathematical rule.
This method is generally adopted for small surveys where high precision is not required. Since corrections are applied manually, the accuracy of the adjusted traverse depends largely upon the experience of the surveyor.
- Simple and quick adjustment technique
- Suitable for rough and preliminary surveys
- No fixed mathematical relationship is used
- Not suitable for precise engineering projects
Important Note: The Arbitrary Method is rarely used in modern engineering surveys because more accurate analytical methods are available.
Bowditch’s Rule
Bowditch’s Rule, also known as the Compass Rule, assumes that both linear and angular measurements are of nearly equal precision. The total correction is distributed proportional to the length of each traverse side.
It is one of the most widely used traverse adjustment methods in engineering surveying.
- Suitable for ordinary engineering surveys
- Commonly used in compass traverses
- Corrections proportional to line lengths
- Easy and reliable adjustment method
Graphical Method
In the Graphical Method, the traverse is plotted to scale on drawing paper, and the closing error is adjusted graphically by shifting the traverse lines proportionally.
The error of closure is represented graphically and corrections are distributed visually among the traverse sides. This method is easy to understand but less accurate than analytical methods.
- Used mainly for approximate graphical adjustments
- Simple plotting-based approach
- Suitable for small surveys
- Less accurate compared to Bowditch and Transit Rules
Important Note: Plotting accuracy directly affects the final adjusted traverse in the Graphical Method.
Transit Rule
Transit Rule assumes that angular measurements are more accurate than linear measurements. Therefore, corrections are distributed proportional to the latitudes and departures of traverse lines.
- Suitable for transit surveys
- Used when angular observations are highly precise
- Corrections based on latitude and departure values
- More suitable for precise angular measurements
Axis Method
In the Axis Method, corrections are distributed with reference to a selected axis. The traverse is adjusted by balancing errors along chosen coordinate axes.
This method is generally used in special engineering surveys where alignment with a specific reference axis is important.
- Used for special adjustment requirements
- Corrections applied with respect to a selected axis
- Useful in route and alignment surveys
- Requires careful computation and plotting
Important Note: The Axis Method is less commonly used compared to Bowditch’s Rule and Transit Rule.
Comparison Between Bowditch Rule and Transit Rule
| Bowditch Rule | Transit Rule |
|---|---|
| Corrections proportional to line lengths | Corrections proportional to latitudes/departures |
| Assumes equal precision in angles and distances | Assumes angular measurements are more precise |
| Suitable for compass traverses | Suitable for transit surveys |
| Most commonly used method | Used in precise angular surveys |
Conclusion
Traverse adjustment methods are essential in surveying for eliminating closing errors and improving computational accuracy. Among the various methods available, Bowditch’s Rule and Transit Rule are the most widely adopted in practical engineering surveys.
The selection of the appropriate method depends upon the relative precision of angular and linear measurements and the nature of the engineering survey.
References
- Surveying Vol. I by B.C. Punmia
- Surveying and Levelling by T.P. Kanetkar
- Higher Surveying by S.K. Duggal
- Engineering Surveying Notes and Manuals
- IRC Surveying Standards and Engineering References
Author
Prepared By: Mohan Dangi (Gold Medalist)
This article has been prepared for students, surveyors, civil engineers, and competitive examination aspirants to understand the methods of traverse adjustment in surveying.
Disclaimer
This content is intended for educational purposes only. Always refer to standard surveying textbooks and professional field manuals before applying these methods in actual engineering practice.
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