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In the two examples, the measured offsets are:
•
Example 1: X = 0.9, Y = 1.8.
•
Example 2: X = -0.5, Y = -1.5
The Z / height value to the mounting plate measurement datum point has been assumed to be 1.0 m, but this must
also be measured from the IMU/CoG.
Sign conventions may differ between different navigation packages.
The lever arm may be measured with a tape measure or with professional survey equipment. Either way, the
suggested tolerance for measuring these distances is <5 mm. A measurement outside of this tolerance may result
in a lower quality calibration.
To establish the most accurate values it is recommended to carry out this measurement while the vessel is in a dry
dock. If this is not practical, then the measurements can be taken from the nearest known point. For example, the
XYZ lever arm of a nearby GNSS antenna may be known. The mounting plate measurement datum point can
therefore be offset from this point if it is easier than measuring all the way back from the IMU/CoG. However, the
final lever arm values must always relate back to the IMU/CoG.
Forward / Y positive
Starboard / X positive
Example 1
Merlin measurement
datum point is:
X = 0.9 m
Y= 1.8 m
Z = 1.0 m (assumed)
Example 2
Merlin measurement
datum point is:
X = -0.5 m
Y= -1.5 m
Z = 1.0 m (assumed)
Vessel IMU/CoG
X = 0.0 m
Y = 0.0 m
Z = 0.0 m
Figure 19 Examples of offsets to the mounting plate measurement datum point
