The vessel coordinate system

A main function of the parameters required for system installation is to inform the system of the relative positions between the various sensors and the angular orientation of the sensors with respect to the vessel. A reference point somewhere on the vessel has to be selected, and a Cartesian right-handed coordinate system - as shown in the figure below - must be defined with its origin in the reference point. The location of this reference point has no physical significance - it may be anywhere on the vessel. The placement of the various instruments must be identified with forward, starboard and downward coordinates in this coordinate system.

The forward axis (X) must be parallel to the vessel keel, and the downward axis (Z) must be vertical when the vessel is trimmed normally. The plane defined by the forward and starboard axes will then be horizontal, and the attitude sensor should then, if properly installed and calibrated, measure zero roll and pitch with a normally trimmed vessel lying still.

Forward position (X)

Forward position is defined on the X-axis (refer to the illustration below). Locations further forward than the reference point are positive.

Downward position (Z)

Downward position is defined on the Z-axis (refer to the illustration above). Locations below the reference point are positive.

Starboard position (Y)

If a sensor location is on the starboard side of the reference point, the value will be positive.