Scenario: GPS Emulation

The focus of many ROV users is on underwater exploration, not on the nuts and bolts of integrating new electronics with an already-complex set of hardware and software. The Cerulean DVL can emulate a standard GPS (it comes from the factory already set to do so). This is accomplished by setting the DVL to send only the NMEA-format $GPRMC message. All other data output, information messages, and warning messages are suppressed. The emulation works on both serial and Ethernet interfaces.

Note that the DVL can’t magically geo-locate all by itself. At power-up, it therefore begins life thinking it is at latitude/longitude (0N,0E), which is somewhere off the coast of Gabon, Africa. You can continue to operate using relative changes from (0,0), or you can operate in true latitude/longitude by setting a new initial position using a known starting location [the optional GPS can automatically provide an initial position].

What this requires in addition to the DVL: For operation relative to (0,0), connect the serial output of the DVL to a serial port where your ROV software is expecting to find a GPS. To operate in true latitude/longitude, you can then send a starting position from your own GPS to the DVL, you can add an optional GPS directly to the DVL and let the DVL manage it (the GPS should be located on the ROV so it loses fix when the ROV submerges), or you can send a position fix directly to the DVL when the ROV is at a known location like a waypoint.

Also, see the introductory discussion of the IMU for additional considerations for this scenario.

GPS Emulation. The “Serial-RX” line connects to the ROV port that expects a GPS to be connected. In this scenario, the Serial-TX line (sending from the ROV Systems to the DVL) need not be connected. This is probably the simplest DVL interconnection schema.

GPS Emulation, Take 2. The “Serial-TX” line can be added (the other half of the serial interface), probably connected to a different serial port on the ROV Systems than the Serial-RX of the GPS emulation. Now, you can continue to use the GPS emulation, but you can use the TX port to send data to the DVL, such as position updates.