SeaTrac Serial Command Interface Reference
Page 138
9.3.
USBL Local Relative Position Coordinates
On X150 beacons, having resolved the range and incoming USBL signal angle (as an
azimuth and elevation), the position of the remote beacon in the beacon’s local frame
of reference is computed (in metres) and defined in the coordinate frame shown
below…
Coordinates are relative to the beacon’s position, with the origin being the defined as
the centre of the upper beacon housing bulkhead.
Please note that to comply to the earlier ‘attitude’ definition, positive Z axis directions
are defined as “down” (towards the seabed) when the beacon is mounted in the
upright position shown above.
9.4.
USBL World Relative Position Coordinates
On X150 beacons, once a local frame-of-reference position is computed, it is
transformed into the world frame-of-reference using the attitude from the AHRS (or
user specified setting).
World coordinates are provided in a Cartesian Northing, Easting and Depth (NED)
triplet, with values stated in metres. Positive values of depth represent a translation
towards the seabed, while negative values represent a translation towards the surface.
