P a g e |
22
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 Merlin LT 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.
4.3.2 Determining the vertical laser offset adjustment
The vertical laser offset adjustment is the adjustment of the lever arm from the measurement datum point on the
base plate to the laser origin point inside the Merlin LT.
The vertical laser offset adjustment is dependent on the vertical angle that the Merlin LT has been positioned at,
and on the direction – fore or aft – that the Merlin LT is pointing on the vessel.
In the table below, select the relevant row according to the vertical angle at which the Merlin LT is secured. Then
read off the XYZ values from the vertical columns, depending on whether the Merlin LT is facing fore or aft.
Measurements are in metres and are taken from the measurement datum point on the top of the base plate. To
measure a vertical laser offset adjustment from the bottom of the base plate, add 0.01 m to the relevant Z value.
Merlin LT
vertical angle
Merlin LT pointing aft
Merlin LT pointing fore
X
Y
Z
X
Y
Z
0
0
0
0.354
0
0
0.354
45
0
-0.082
0.302
0
0.082
0.302
90
0
-0.116
0.220
0
0.116
0.220
Table 1 Vertical laser offset adjustment
Measurement datum
point in the centre of
the base plate
Laser origin point
inside the centre of the
rotating scanning head
Vertical laser offset
adjustment: ‘Y’
Vertical laser offset
adjustment: ‘Z’
Figure 18 Vertical laser offset adjustment
