Survey Reduction

After a successful traverse adjustment or where the station coordinates are already known for each setup, the next stage in processing the survey can continue.  This is called Reduction as is the name given to turning HaVaSd observations into XYZ coordinates.

To start this process right click the job folder for the survey and select Reduction.

The reduction dialog will then be displayed.  Each setup is listed and beside each a status symbol of some sort.  Moving across the status of the setup is listed, then the Station it backsights and in turn its status.

A setup can only have its observations properly reduced if both it and its reference station have a status other than Unknown. A Derivable setup is one that relies on another.  In the case above, I2 depends on A. It can't be seen in this view but I2 is a side shot from A and as such will be calculated automatically when A is reduced. Sometimes the reduction process needs to be run multiple times when setups generate new stations, which are then resected off of later in the job. In that case the resection/free station calculation needs to happen manually (so the results can be checked), after which the reduction can be run again to properly reduce the remaining free station setups.

A setup can have the following symbols indicating their readiness:

•  The setup can not be reduced because either its station or the reference station are unknown.
•  The setup can be reduced, but one or more tolerance checks has failed.  The number of failed checks is written next to it.
•  The setup can be reduced with all tolerance checks passed.

Where a setup whos occupied station coordinates are some type of known, and the backsight station is too, then an RO Review can be calculated.  This compares the known distances between the stations with that derived from the backsight observations.  Any differences are presented below when the setup is selected from the list.

The tolerance settings then define the degree to which a user is alerted when an ro review for a particular setup falls outside of acceptable limits.  So for monitoring jobs where highly accurate 1" instruments are being used these tolerances would be lowered to 1mm for instance.  But for typical earthworks jobs this can be raised to 5mm as absolute accuracy is not so important or generally achieved.

When the Ok button is pressed, n4ce will further warn the user if any tolerance checks are still failing.  So at no time can errors be missed by clicking to fast though the reduction process. 

Configurable options for this process are:

• Generate Report: Displays the text report which backups up the ro review checks.  If a traverse has just been performed prior to the reduction, then the reduction report will be appended to the end of the traverse report.
• Reduce Derived: If a station is Unknown, but is observed later by a setup that can be reduced, then n4ce will go back and reduce the setups if they later become derivable as a result. 
• Average Backsights: Where more than one observation is taken to the backsight object, the observations will be averaged and the resultant reading used for the ro review and setup orientation.