Gravity Measurements in SA
The ability to measured the orientation of gravity is an important part of metrology for a number of reasons. The first step in gravity measurement is prepare the instrument and then take a measurement. These controls are covered within the instrument guides. For laser trackers that would Here.
Measuring Level
When a gravity measurement is take within SA, this measurement is made relative to the instrument’s standing axis and is recorded as a Frame.
The Z-axis of this frame points upward along the gravity vector, and the XY plane of this frame defines the gravity plane. This frame measurement is saved directly on the instrument’s head such that the origin of the level frame is at the center of the instruments base frame and at the center of rotation for all angular point measurements.
Gravity Measurement Frames
You can measure level at any time and you can also measure level multiple times from the same station. Like any measurement there will be some minor variation between these level measurements. Level measurement frames are automatically associated to the instrument station. That association means that if you were to move an instrument or locate it, the measured level frame automatically moves with the instrument, as an additional measurement, and will maintain its orientation with respect to the instrument’s base frame.
If the level frame is moved for some reason or gets disconnected from the instrument this connection can be re-established using the option Reset Associated Object Transforms. This works with any cloud or 6D measurement as well.
If you wish to average multiple level measurements you can use the frame construction command (Construction> New Frames> From Objects> Frame as Average of Object Frames). However, this average frame will not be automatically associated with the instrument. To link it to the instrument station use: Instrument> Object Association>Associate Objects with Instrument. This will link the new frame to the instrument station as a measurement.
How to use level Measurement?
It is important to understand that taking a level measurement does not change your measurements or compensate the instrument, it simply records the current orientation of gravity with respect to the instrument’s position. An additional step is required in order to perform a level compensation.There are two very distinct and separate paths you can use for level measurement:
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External Compensations such as Leica's Orient to Gravity (OTG) or API's Virtual Level (VL). These involve a compensation process preformed outside of SA.
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Straighten within SA allows you to directly measure and correct for gravity using the measurements within the application.