POS MV V4 User Guide
Installation
Copyright © Applanix Corporation, 2009
2-46
The vessel centre of rotation is a point of the vessel that experiences only
rotations with changes in attitude. Any heave measured at this point arises
entirely from vertical movements that affect the whole vessel equally.
The multi-beam transducer will be some distance from the vessel centre of
rotation. The transducer will therefore experience a small component of heave
as the vessel moves vertically in the water and a much larger component of
apparent heave with changes in vessel attitude.
To separate these effects, POS MV translates the IMU measurements to the
vessel centre of rotation. Having done so, it applies filtering to the
measurements of pure heave as explained in the
Theory of Operation on
page
B-1 and then translates the filtered measurements back to the positions
of sensors 1 and 2.
This method for measuring heave avoids the errors that can occur if you filter
direct heave measurements made from a point remote from the vessel centre
of rotation.
Measure and record the distance from your reference point to the vessel
centre of rotation. Make these measurements to an accuracy of ±0.05 m
(~±2 in):
• A positive value for the X lever arm means the vessel centre of
rotation is forward of your reference point
• A positive value for the Y lever arm means the vessel centre of
rotation is to starboard of your reference point
• A positive value for the Z lever arm means the vessel centre of
rotation is below your reference point
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