In order to hold level during an alignment an instrument must first be straightened so that its level measurement frame is aligned with the working gravity frame. This is accomplished by using the Straighten commands.
Align Instrument Z Axis with Working Frame. This command is only used with Total Stations or other instruments with an active compensator or stations that have had a level compensation performed outside of SA. In this scenario the base frame, or origin of the tracker model is already aligned with the gravity measurements from this instrument and all that is needed is to straighten the instrument model within the job file. Once complete its possible to verify the Straighten operation by checking the instrument's transform directly (through the instrument properties). The Rx and Ry tilt with regard to the working frame should read exactly zero when complete.
Align Level Frame Z-axis with Working Frame. This second option is used for instruments that measure level within SA and record a level measurement frame. This command offers the opportunity to select the level measurement in order to alignment the instrument. It will orient the instrument in the job file such that the selected level frame is aligned with the working frame, rather than the instruments base frame. This is the typical option for laser trackers.
A graphical indicator of the current status of a stations orientation to a gravity reference can be enabled through the station right-click menu:
This monitor compares the relative Rx and Ry rotations between the two selected frames:
Reference Frame. Which represents the base coordinate within the job file that indicates the direction of gravity. By default this will be the WORLD frame.
Level Frame. Which represents the instruments level measurement reference. For compensated instruments this will be the instrument base, but a level measurement should be selected for non-compensated instruments. The selection for the frame references are available directly in the station's right-click menu:
Any time the instrument station Reference frame and Level frame are aligned within the specified Reference Frame Alignment Tolerance the instruments status indicator will be displayed in green, while the status indicator will display in red if the instrument model is tilted relative to the reference frame in the job file: