Short Answer:

The transit rule in traverse adjustment is a method used to correct errors in a closed traverse by distributing the total error based on the latitude or departure of each traverse line. Unlike the Bowditch rule, which considers line length, the transit rule is applied when the angular measurements are more accurate than the linear measurements.

This rule is useful in situations where distances might not be measured with high accuracy but angles are reliable. It helps balance the errors and ensures the adjusted traverse closes properly, allowing for precise plotting and calculation of coordinates.

Detailed Explanation:

Transit rule in traverse adjustment

The transit rule is one of the methods used to adjust a closed traverse by correcting the closing error in measured latitudes and departures. It is mainly applied when the angles measured using a theodolite are considered highly accurate, while distance measurements may have small errors due to chain or tape stretching, slope, or other field difficulties.

When a closed traverse is completed, ideally, the total sum of latitudes (north-south values) and departures (east-west values) should be zero. But in actual surveys, small differences or errors remain due to imperfections in measurement. The transit rule is used to correct these errors and distribute them proportionally based on the size of each latitude or departure, not the length of the line.

When to use the transit rule

• When the angular measurements are more precise than the distance measurements.
• In surveys where theodolites or total stations are used for accurate angle readings.
• When the lengths of lines are doubtful due to slope, sag, or poor chaining.

Steps to apply the transit rule:

1. Measure all interior angles and line distances during the fieldwork.
2. Calculate bearings for each line from the angles.
3. Compute latitude and departure of each line using:
   • Latitude = Length × cos(Bearing)
   • Departure = Length × sin(Bearing)
4. Add all latitudes and departures to find the total misclosure (error).
5. Apply the transit correction formulas:
   • Correction to Latitude of a line = (Latitude of the line / Total sum of latitudes) × Total error in latitude
   • Correction to Departure of a line = (Departure of the line / Total sum of departures) × Total error in departure
6. Adjust each line’s latitude and departure by adding or subtracting the calculated correction.
7. Recalculate the coordinates of all stations using the corrected values.
8. Plot the traverse with the new coordinates to ensure proper closure.

Key differences from Bowditch rule:

• Transit rule uses the magnitude of latitudes and departures for error distribution.
• Bowditch rule uses the length of each line for distributing the error.
• Transit rule is more accurate when distance measurements are less reliable.

Advantages of transit rule:

• Suitable for long traverses where chaining may introduce greater error.
• Helps in reducing the influence of poor distance measurements.
• Ensures proper closure of the traverse even when distances are not exact.
• Can be used in various civil engineering tasks like boundary layout, land development, and site planning.

Conclusion

The transit rule in traverse adjustment distributes the total error based on the size of the latitude and departure of each line. It is best used when angles are accurate, but distances may have small errors. This method helps achieve a balanced and corrected traverse for accurate plotting in civil engineering works.