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4.3.3 Apply the vertical laser offset adjustment to the measured XYZ lever arm
The vertical laser offset adjustment can now be applied to the initial physical XYZ lever arm measurement.
From the examples in section 4.3.1:
Example 1 – assuming the Merlin LT is set at 90° vertical angle:
•
Measured offsets: X = 0.9, Y = 1.8, Z = 1.0
•
Vertical laser offset adjustment (Merlin LT pointing fore; 90° vertical angle): X = 0.0, Y = 0.116, Z = 0.220
•
Final lever arm offset: X = 0.9 m, Y = 1.916 m, Z = 1.220 m
Example 2 – assuming the Merlin LT is set at 45° vertical angle:
•
Measured offsets: X = -0.5, Y= -1.5, Z = 1.0
•
Vertical laser offset adjustment (Merlin LT pointing aft; 45° vertical angle): X = 0.0, Y = -0.082, Z = 0.302
•
Final lever arm offset: X = -0.5 m, Y = -1.582 m, Z = 1.302 m
Take care to apply the negative / positive adjustments correctly.
4.4 Lever arm offset measurement when using the mounting plate
If you are
not
using the mounting plate, please skip this section.
The purpose of this section is to outline the process necessary to calculate the lever arm when using the optional
Merlin LT mounting plate. The lever arm is the position of the Merlin LT laser origin point in relation to the vessel’s
IMU/CoG. The laser origin point is inside the Merlin LT, at the centre point of the laser’s horizontal rotation.
The lever arm is expressed as an XYZ coordinate on the vessel reference frame. This coordinate is entered into
the navigation software and ensures that data from the Merlin LT is correctly positioned in relation to data received
from other onboard sensors and survey equipment.
Note that a calibration must also be carried out prior to the start of survey operations in order to fine tune the
heading, pitch and roll angles of the Merlin LT data with respect to the IMU. See the accompanying Merlin manuals
for QINSy, HYPACK and PDS for further details on this process.
The workflow for carrying out the lever arm offset measurement is as follows:
•
Secure the Merlin LT mounting plate in position.
•
Establish the physical XYZ lever arm to the measurement datum point on the mounting plate.
•
Bolt the Merlin LT on the mounting plate at the desired horizontal angle.
•
Position the Merlin LT at the desired vertical angle.
•
Determine the vertical laser offset adjustment from Table 2 or Table 3.
•
Apply the vertical laser offset adjustment to the measured XYZ lever arm.
•
Enter the final lever arm into your navigation software.
The final lever arm values are dependent on the horizontal and vertical angles at which Merlin LT is positioned.
These values will therefore change as Merlin LT is reoriented. Each time the unit is moved from its fixed position,
