Kongsberg Simrad EK80 Installation Manual page 64

Simrad EK80 Installation Manual
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 on a depth sensor, 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.
The X-axis is the
A
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).
The Y-axis is the transverse direction of the vessel, and in parallel with the deck.
B
A positive value for Y means that a sensor or a reference point is located on the
starboard side of the reference point (origin).
The Z-axis is vertical, and in parallel with the mast. A positive value for Z means
C
that a sensor or a new reference point is located under the reference point (origin).
Reference point (Ship Origin)
D
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 antennas, echo sounder and sonar transducers, motion reference units, etc.) are
referenced to the origin. In most cases, the location of the vessel's "official" origin
has been defined by the designer or shipyard. This origin is normally identified with a
physical marking, and also shown on the vessel drawings.
Frequently used locations are:
• Aft immediately over the rudder (frame 0)
• Vessel's centre of gravity
• The physical location of the motion reference unit (MRU)
62
394149/D