Kongsberg Simrad ST90, Reference Manual

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Vessel coordinate system
The vessel coordinate system is established to define the relative physical locations of
system units and sensors.
When you have several different sensors and transducers on your vessel, and you wish each
of them to provide accurate data, you need to know their relative physical positions. The
antenna of a position sensor is typically mounted high above the superstructure, while a
motion sensor is located close to the vessel’s centre of gravity. Both of these are physically
positioned far away from the transducer, which may be located closer to the bow. Very often,
the information from one sensor depends on data from an other. It is then important that the
relevant measurements are compensated for these relative distances.
Example
If you wish to measure the actual water depth, you will need to know the vertical
distance from the echo sounder transducer to the water line. Since the vessel’s
displacement changes with the amount of cargo, fuel etc, the physical location of
the water line on the hull must either be measured at a regular basis, or measured
with a second sensor.
In order to establish a system
to measure the relative distance
between sensors, a virtual
coordinate system is established.
This coordinate system uses three
vectors; X, Y and Z.
A
The X-axis is the longitudinal
direction of the vessel, and
in parallel with the deck. A
positive value for X means
that a sensor or a reference
point is located ahead of the reference point (origin).
B
The Y-axis is the transverse direction of the vessel, and in parallel with the deck. A
positive value for Y means that a sensor or a reference point is located on the starboard
side of the reference point (origin).
C The Z-axis is vertical, and in parallel with the mast. A positive value for Z means that a
sensor or a new reference point is located under the reference point (origin).
D
Reference point (Ship Origin)
Coordinate system origin
The origin is the common reference point where all three axis in the vessel coordinate
system meet. All physical locations of the vessel’s sensors (radar and positioning system
Concept descriptions