Theodoloite Traversing | Traverse Computation Example | Surveying

GALE’S TRAVERSE TABLE: 

Traverse computations are usually done in a tabular form, a more common form being Gale’s traverse table. The following computations are made in the Gale’s traverse table.

1.  The sum of all the interior angles should be (2N – 4) x 90°, where N = Number of sides of a traverse. If the sum of all the interior angles is not equal to (2N – 4) x 90°, the error is distributed equally among the angles and the angles are corrected.
2.  Calculate whole circle bearings of other lines using the measured bearing of the first line and corrected interior angles.
3. Compute reduced bearings (R. B.) from the W. C. B.
4. Using measured length of each line and computed R. B., calculate latitude and departure of each line (i.e., calculate consecutive coordinates of each line). Latitude = L = l cosθ, Departure D = l sinθ 
5. For consecutive coordinates of point B, length of line AB and R.B. of line AB are used and for consecutive coordinates of point C, length of line BC and R.B. of line BC are used.
6.  Calculate difference between Northing and Southing and Easting and Westing. These differences give the closing error.
7.  This error can be removed by applying necessary corrections to latitudes and departures. Corrections to latitudes and departures are applied using Bowditch’s rule or transit rule.
8. Find corrected latitudes and departures. The sum of Northing must be equal to the sum of Southing. The sum of Easting must be equal to the sum of Westing.
9. Compute independent co-ordinates from the corrected consecutive co-ordinates. The co-ordinates of first point are assumed. The co-ordinates of first point are assumed in such a way that the independent coordinates of all the points are positive and the whole of the traverse lie in the first quadrant.
10. Calculate: Closing Error, Direction of Closing Error and Relative Error of Closure

Gale’s Traverse Table

Closing Error, Direction of Closing Error and Relative Error of Closure:

Calculations