The backsight dialog has “Setup” and “Results” tabs showing the results of a measurement to the backsight.

• Set Angle Option List: There are 4 backsight options for setting the reference angle.  They are found in the option list in the upper left of the Take BS screen:

Set to Zero: This is the most common usage.  A message is sent to the instrument to set it to zero, then the backsight is taken at a zero reference angle, and angles then are typically turned to the right from zero.

Set to Backsight Azimuth: In this scenario, the backsight direction in the gun is set to the azimuth of the backsight.  If the backsight azimuth was 180 degree, then an angle to the right of 10 degrees would read 190 degrees from the instrument.  This is useful in underground mine surveying because it keeps the readings displayed by the total station always referring to true azimuth.  Some surveyors are “azimuth” surveyors and others prefer “set zero”.

Set to: User-Entered Azimuth: This option allows the user to “force” a particular backsight azimuth into the total station as a reference direction.  Sometimes non-zero backsight angles are deliberately entered in set collection, to use different quadrants of the 360 circle.

Use Current (Do Not Set Angle): Uses whatever direction reading is already in the instrument.

• Set Angle and Read: This button will set the horizontal angle and read the distance to the backsight. The program defaults to the “Set Angle and Read” option (the large, lower button), on the assumption that most often, you will be taking a distance measurement to the backsight.
• Set Angle: This button will only set the horizontal angle. If you are just backsighting an object or plumb bob without a measurement, choose “Set Angle”.  You can tap Set Angle on the screen or using the keyboard, enter Alt S.  (The underlined letter can access the button in question by entering Alt and the letter.  Alt A would go to “Check Angle”.)
• Check: This enables the surveyor to determine whether the instrument has "drifted off" the point. Based on what is presented here, the surveyor may decide to reset the BS angle, or to actually re-level and re-shoot the BS point.   More commonly, you would do a Check Backsight after taking a lot of foresights.  You may want to be sure you haven’t bumped the instrument or experienced settlement in the tripod legs.
• Check Angle: This button will simply read the angle currently in the instruemnt and compare it to the reference angle. Choose Check Angle to re-sight on the backsight and obtain an angular error report (no distance comparisons are made).
• Turn to BS: With robotic total stations, you have the option to “Auto Turn to Backsight”. This button will turn the instrument to the known backsight angle previously set so that a Check or Set can be performed. Once you OK back to the foresight screen, the instrument will automatically prompt if you want to return to the previous foresight position.

Whether in a conventional or Manual Total Station configuration, pressing Set Angle and  Read or pressing Enter initiates a Take BS shot.  In Manual Total Station configuration, it will lead to a dialog where you input the angle and distance measurements.

When you press Enter, or tap OK, this leads to the foresight screen, where shots are taken, readings are presented and points are plotted graphically.

Types of Total Station Backsights - Handling Missing Information

The SurvCE backsight procedure will allow “last minute” entry of the backsight coordinate values if none are found, or will calculate the backsight coordinates using the azimuth and distance of the measurement.  If both the Station and Backsight have coordinates (non-zero northings, eastings and elevations), the backsight azimuth is computed, and the coordinate values are not altered.

Known Station and Backsight Azimuth to Backsight Point of Unknown Coordinates

A Backsight Point will be calculated.  Note that when a zero-coordinate backsight point is encountered, the program will ask the user to Enter Coordinates or Use Azimuth.  This prompt appears only when the Use Azimuth option has been selected.  If you choose only to Set Angle, the backsight point will not be calculated, obviously, but is still a viable entry in the raw file.  Some raw file processing programs like Caice make use of this backsight point with zero coordinates but used as a backsight azimuth reference.  It is recommended that you use distinct, new point ID’s for all foresight points.  Don’t re-use a backsight point ID that served as a “dummy” point to initiate the “set zero” backsight, unless you plan to re-use it for the same backsight again.