Spectra Precision FAST Survey Reference Manual - Manual (Page 125)

p123
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.
 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 in most cases, 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. (Note: On most buttons, the underlined letter in the name is the hotkey which, in combination with the
ALT key, will access the function of the button. On this menu, for instance, 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 large set of foresights. You may want to be sure
that 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 instrument 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 automatically turn to the backsight. This button will
turn the instrument to the previously set backsight angle so that a Check Angle or Set Angle can be performed.
Once you press OK to go 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 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 completes the backsight setup and 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 FAST Survey 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.
Orientation (Remote Benchmark)
This is a command for total station applications only, in which the elevation of one or more remote, but known, points is
used to compute the elevation of the occupied Station. The Remote BM tab is the 2nd to the right in the Backsight
screen. The main screen is shown below.