Traverse Adjustments: Comparing Methods

This topic compares the adjustment computation methods used by Trimble Access (TA) and Trimble Business Center (TBC) so that you can better understand the advantages of performing the adjustment in TBC. It includes the following sections:

• First vs. last MTAs (mean turned angles)
• Equal weighting on MTAs
• Curvature correction
• Weighting of angle adjustment
• Managing bad observation data in TA

First vs. last MTAs

TA and TBC both attempt to use a single mean turned angle (MTA) to compute the angles and distance to a backsight or foresight. However, when there is more than one MTA to the same point, a difference can exist. In this case, TBC uses the last recorded MTAs for computing the traverse, which matches the way it adds coordinates and makes other changes to the project. The last value to be typed in and the last coordinate added to a point is the one that is kept. TA, on the other hand, uses the first MTA it encounters.

Equal weighting on MTAs

TA and TBC both use measurements in both directions (reciprocal observations) to compute the horizontal and vertical distance changes between stations. However, these measurements are often MTAs, which can have a variable number of actual total station observations inside. For example, the foresight MTA from station A to B may consist of 10 total station observations, whereas the backsight from B back to A may consist of five total station observations. TA averages both of these MTAs; that is, it treats the 10-observation MTA with the same weight as the 5-observation MTA. The proper behavior is to weight the 10-observation MTA twice as much as the 5-observation MTA. TBC includes project settings for this that currently default to the weighted mean.

Curvature correction

For curvature corrections, TA and TBC both use the radius of curvature in the direction of each observation reduction.

Weighting of angle adjustment

For weighting of angle adjustments, TA and TBC both use the same weighting for angle adjustments.

Managing bad observation data in TA

TA uses the MTA record for its calculations whereas TBC uses the original F1 and F2 observations. MTA records in TA are not updated if F1 or F2 observations are later edited, and you cannot delete MTA records from Review job in TA. You can delete the F1 and F2 observations from Review job in TA, and this will give you the correct answers when the data is processed in TBC. But the better solution to get the correct answers in TA and TBC is to take action when TA detects there are observations out of tolerance. When the Observation: Out of tolerance screen is displayed, set the Action in TA to Overwrite those observations. This will delete the previous F1 and F2 observations as well as the MTA record to that point.