# Scenario: Using GPS Assist

The DVL can accept $GPRMC messages from various sources, including a GPS connected to the DVL, or from either the serial or Ethernet command interfaces. The DVL assumes the GPS is on board the ROV. As long as the GPS indicates a good fix, the DVL will send the GPS current position as the ROV position. It will also reset the DVL current position to track the GPS output. As soon as the GPS fix drops out, the DVL will switch over to using dead reckoning. If the ROV surfaces, the DVL will switch back to the GPS position and reset its current position to the GPS value. We assume when the GPS dives, it dives straight down until it achieves DVL lock.

During the course of the dive, the DVL can still accept other position updates such as known waypoints.

See the figure below.

**What this requires in addition to the DVL**: This requires a GPS on board the ROV, either directly connected to the DVL or connected to another computer that can relay the $GPRMC message to the DVL.

![Sequence of a GPS-assisted dive](/files/90VhdHEmnGSQMZ0RXllB)


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