ROV Locator Startup

The ROV Locator has a complicated start-up sequence. Most of the start-up order tolerance is built into this device. Except as noted below, the start-up is the same for the ROVL Mk II and Mk III systems.

1. The ROVL Mk II transmitter and Mk III transponder power up quickly and do not require interaction with the other Omnitrack subsystems to begin working. As usual, the Mk II transmitter requires exposure to GPS signals to begin cycling.

2. The ROVL Mk II receiver and Mk III transceiver power up quickly. As usual, the Mk II receiver requires exposure to GPS signals to synchronize its timebase.

3. The GNSS compass antennae used in the Omnitrack system require time to acquire a satellite fix upon power up. In order to do so, they need an unobstructed view of the satellite constellation. A position fix is usually available before a heading output is available. A position fix typically takes 15 to 30 seconds given an unobstructed sky view. A heading fix may take a minute or more.

4. As the receiver/transceiver is starting up, it is simultaneously doing the following:

   • Initializing its IMU to provide roll and pitch, and to provide magnetic heading whenever the GNSS compass is not providing a heading. This happens within a few seconds, but you may observe the system heading changing during this time.

   • Waiting for the GNSS compass to provide a position fix.

   • Waiting for the GNSS compass to provide a heading fix.

   • Looking for the ROV's MAVLink server to come on line.

   • Cycling to locate the ROV via the ROVL transmitter/transponder.

5. The receiver/transceiver independently cycles to locate the ROV, and independently can output the NMEA-like messages $USRTH and $USTLC without any of the other subsystems being ready. These NMEA-like messages are not used in the Omnitrack function and can be safely turned off to reduce network traffic. Note that the Cerulean SonarView application makes use of the $USTLC message to facilitate situation visualization.

6. Once the MAVLink server in the ROV is detected, a communication channel to it is opened. The step below cannot happen until this is complete.

7. When a GNSS position fix is available, the receiver/transmitter attempts to send a global origin to the ROV. If the ROV is detected to already have a global origin set by other agents, the receiver/transmitter opts to use the existing global origin. Once a global origin is set, the ROV should be able to do position hold based on either Tracker 650 inputs or on ROVL position fixes if a Tracker-650 is not installed.

8. Once the ROV is detected by the ROVL system, and a position fix is available, and a heading fix is available if configured to require this (otherwise a magnetic heading could be used), a position estimate referenced to the global origin is sent to the ROV. Once accepted by the ROV, the ROV will be able to report its geo-referenced position to other software such as QGroundControl, and it will be able to do higher-level functions such as waypoint navigation.

9. The receiver/transceiver will continue to send position estimates to the ROV to maintain a correct geolocation.

10. If the ROV MAVLink connection is lost, the receiver/transceiver will restart at step 6.