The backsight dialog has SETUP and RESULTS tabs showing the results of a measurement to the backsight.
Set to Zero: This is the most commonly used option. A message is sent to the instrument to set it to zero, then the backsight is taken at a zero reference angle. Angles are then 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. For example, if the backsight azimuth is 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 ensures that the readings displayed by the total station always refer to true azimuth. Some surveyors are “azimuth” surveyors and others prefer “set zero”.
Use Current (Do Not Set Angle): Uses whatever direction reading is already in the instrument.
Whether in a conventional or Manual Total Station configuration, pressing Set Angle and Read or pressing Enter will cause a backsight to be taken. In Manual Total Station configuration, a dialog will appear for you to manually input the angle and distance measurements.
Pressing Enter or OK complete the backsight setup and lead 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
In the case that the coordinates of the station are known and you shoot a backsight point of unknown coordinates, a backsight point will be calculated. Note that when a zero-coordinate backsight point is encountered, the program will prompt 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, but is still a viable entry in the raw file. Some raw file processing programs make use of this backsight point with zero coordinates as a backsight azimuth reference. It is recommended that you use distinct new point IDs 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.