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Part No. 96000001
7.5 Measuring IMU Offsets
Figure 158: IMU Reference indicators
Identify the COG of the vessel that point becomes the reference point of the INS offsets. The
POS/MV uses a right-hand Cartesian coordinate system. Therefore, the lever arm offsets should be
measured as
+X = To Bow
+Y = To Starboard
+Z = Down
When using DGPS, offsets should be measured to 5cm accuracy. When using RTK, offsets should be
measured to 5mm accuracy.
Measure the offset from the reference point to the primary GPS antenna and record it in POSView in
the “ref. to Primary GPS Lever Arm” fields. There is no need to measure the offset of the second
antenna; the Applanix GAMS calibration will determine this X offset.
Measurement of the IMU COG is critical. The IMU has two reference points. On top of the IMU is
the horizontal reference for the X and Y measurement. The vertical Z reference is measured to the
reference point on the rear part of the IMU. After measuring the reference to IMU offsets, input the
values in the “Ref. to IMU Target” fields in POSView Be sure to check the box by “Enable Bare
IMU”, as seen below. NOTE: Some older versions of POSView will not have this option. If not, please
install the version preloaded on the R2Sonic CD that shipped with the Sonar.
Reference
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