Running a Traverse Adjustment

The first stage in computing a traverse is to select the data source which contains the traverse observations. For this example, we will be using the CPD2 log file which can be found in the n4ce Training folder. 

To start the traverse calculation, simply right-click the CPD2 job folder and select Traverse.

Note that we could select Reduction from this menu if all the stations along the traverse route already existed under the Stations folder.  This would bypass the whole Traverse procedure as the coordinates of the stations it's about to calculate are already known and hence can be reduced. For any stations that cannot be computed, you will be expected to enter their coordinates manually.

If the initial coordinates of the control stations are known, they can be entered first under the Stations folder.  This saves having to type them in during the Traverse procedure.  For the example station A has been pre-configured with cords 1000E 2000N and 100Z

After selecting the Traverse option, the following screen will appear.

Each setup is listed on the left, together with their respective control observations.  The first control reading on a setup is assumed to be the backsight and the last is the foresight to the next station in the adjustment. If the order needs to change for whatever reason, then an observation can be re-tasked by selecting it and using the BS, FS and IS (intermediate sight) buttons.  If some need changing, it's perhaps simpler to drag and drop the observations around in the spreadsheet view first (as seen below).

If the order of the observations is changed in the left-hand Setup listing, the changes can be saved by checking "Remember Changes".

Everything is in the correct order for this data already, so the Auto button can be used to extract the route for us. When a sufficient number of setups have been moved over to the right either manually or automatically, the text at its base will change to describe the type of traverse which has been determined.  If this still says unknown after moving the setups over, then the last setup does not foresight onto a fixed point of any kind.

In the example above the Traverse has been identified as a Closed loop traverse as it starts and finishes at the same station. Station I2 has been left behind though as it is a side shot from A and hence not part of the overall adjustment. Press Next to continue.

Once at this stage, the initial misclosures are displayed in the top left-hand corner, together with the coordinates of the start and end stations if applicable.  Below that is the raw traverse before any adjustment is applied.  In a case where the calculated end coordinates are different to those known to be good, then a positional misclosure will result. Likewise, if the bearings or sum of internal angles do not agree with what is known, then there is angular misclosure too.  

The LF Error is a value which tries to measure the overall suitability of the results.  It's derived by taking the sum of the squares of the positional misclosures (in plan) and dividing it by the total length of the traverse. Values of 1 over 15000 are generally assumed to be ok however much higher values may be required by the main contractor in order to ensure new control is properly established and checked.

The Bearing field will be auto-populated with the hz angle of the backsight reading from the first setup to the last. This is used to orientate the traverse and stop it from spinning infinitely about the first station. If this bearing is known, then it can be entered to properly orientate the traverse.  The format for entering the whole circle bearing is DD.MMSS.

Assuming the misclosures are within acceptable tolerances, then the type of report should be set to Full before using the Next button to advance to the adjustment stage.

If the errors are unsuitably large, then the process should be cancelled. Large errors probably point to an issue somewhere with the data and should not just be disregarded. The adjustment will share the error out proportional to the length of each leg. So a large random error will be spread out over the other setups to try and get the traverse to work.

The Adjusted Traverse dialog shows the misclosures after the angular error is first distributed and the current method by which the traverse is calculated. The two choices are Bowditch or Transit. Assuming everything is still within tolerance the Finish button can be pressed which will immediately start up the Reduction stage. When the reduction is complete the reduction report will be added to the bottom of the traverse report so everything regarding adjustments and corrections is in one place.