About adjusting a traverse
Often when generating a traverse, the coordinates of an ending destination are known. ArcMap provides a method to specify this endpoint and determines the difference between the traverse endpoint and the desired endpoint. This difference is known as the misclosure.
ArcMap also provides three different techniques for adjusting the traverse to eliminate misclosure. Each of these adjusting techniques varies in the amount of adjustment of the direction and distance of the individual courses of the traverse. These techniques include:
- Compass correction
- Transit correction
- Crandall correction
The compass correction technique specifies that the misclosure, or difference in x and y between the resulting endpoint and the desired endpoint, are equally distributed among the individual two-point arcs and curves that make up the traverse. This is done by adjusting the location and distance of each arc proportional to the difference in closure. The compass correction technique is the technique most often used to resolve errors in misclosure. It assumes that the errors are related to both errors in the direction measurements as well as the distance measurements. Thus, the corrections are reflected in each distance and direction value. This technique is also known as the Bowditch rule.
Much like the compass correction technique, the transit correction method specifies that the misclosure is equally distributed among the individual two-point arcs and curves that make up the traverse. However, this technique favors the direction measurements over the distance measurements. In determining the location change required of each arc, the proportion assigned to each arc is proportional to the total x or y values of all the arcs. This results in changes that will affect both the direction and the distance of each arc but will alter the distance to a greater extent.
The Crandall correction technique is used when the direction values are assumed to be precise and accurate, and any misclosure is due solely to errors in distance measurements. This adjustment will preserve all the direction measurements and will alter only the distance measurements to eliminate the closure error. Since directions are fixed, the Crandall adjustment can result in unexpected results, such as flipped directions, very long distance adjustments, or no adjustment at all. Use an alternative method in these cases.
With this array of correction techniques, you will be able to not only correct the errors in the traverse but also place greater or lesser value on specific characteristics of the traverse data.