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SeaTrac Serial Command Interface Reference
Page 123
8.4. NAV Protocol Messages
The Navigation protocol builds on the basic range and positioning information produced by the
acoustic transceiver, to provide a set of commands useful for incorporating into tracking and
navigation systems.
As standard, the NAV protocol uses enhanced USBL fixes where the remote beacons depth is
transmitted in the response message. From this, USBL beacons can improve the computed
vertical position solution.
8.4.1. CID_NAV_QUERY_SEND
The CID_NAV_QUERY_SEND command is issued to request the specified remote beacon
respond with the requested information.
Regardless of which information if requested, the response contains an enhanced USBL
message, where the remote depth sensor reading is encoded to a resolution of 1m, and this is
used to compute the vertical Z-axis depth from surface of the position fix. The only exception
to this is when remote Depth information is requested, then this value (to 0.1m resolution) is
used for the Z-axis depth fix.
If successful, the CID_NAV_QUERY_SEND command will start an acoustic message
transmission, and at some time later an acoustic response will be heard.
The NAV protocol handler will generate subsequent serial message to signal when
these event occur.
Additionally acoustic transceiver diagnostic messages are available to monitor activity
and obtain further information on the received signal levels – see section 7.6 on page
92 for further details.
By default the NAV protocol uses an enhanced USBL fix that returns the remote
beacons depth to a resolution of 1m, and this is used to augment the position fix.
However, if the QRY_DEPTH bit is specified in the QUERY_FLAGS field, the remote
beacon will return the depth to an resolution of 0.1m and use this value instead in the
position fix as well as returning it in response message REMOTE_DEPTH field and FIX
structure.
Command Message Parameters
Parameter Type Description
MSG_ID CID_E Command identification code
(CID_NAV_QUERY_SEND)