A Control file is a binary file which is used to store control point co-ordinates and control observations. A control observation is any bearing (direction), distance or height difference observation which is to be used in an adjustment to determine adjusted co-ordinates of control points. A control observation is always therefore an observation to an instrument set up point, or to an existing control point of known co-ordinates, or one of multiple observations to the same unknown point.
A Control file may be processed to determine adjusted co-ordinates of the previously unknown control points. It also may be edited to correct data recording or data entry errors.
Essentially, you will use control files to provide adjusted control when converting data from field observations into objects in the data base. Control files always have an .ADJ extension (CTL in previous versions).
Creating Control Files
You may create a control file and add data to it using the Control File Editor. This editor is run by selecting the Field Transfer/ Resolve/Least Squares Adjustment command.
Control observations may be entered manually in the control file editor. Alternatively control observations may be automatically extracted from a Field File into the control file using the File/Extract command in the control file editor.
Editing Control Files.
Once the data is in a control file, it may be viewed or edited to correct data recording and data entry errors using the Control File Editor.
Adjusting Control Files.
This is the process of performing an adjustment on the contents of a control file. Use the Control File Editor Horizontal menu and Elevation menu to select the adjustment required. The options are:
Horizontal Least Squares
Vertical Least Squares
Transferring Adjusted Co-ordinates to the Data Base.
After an adjustment is successfully carried out, the adjusted values may be transferred to the control file and the Update commands used to transfer the adjusted co-ordinates or elevations to the currently open data base.
When a Field File is reduced using the Resolve/Reduce Field File command, co-ordinates of points which exist in the data base will be used in preference to co-ordinates of the same point identifier located in the Field file.
Therefore, extracting the control from a field file, adjusting the resulting control file, and transferring the results to the data base prior to reducing that field file will ensure that the reduced data from the field file is correctly adjusted.