NMEA Data
432-0012-00-10 Version 110
June 2016
29
The NMEA protocol allows the camera to automatically point toward vessels and other
objects that show up on the display and to track their movement.
The M400 can receive
three types of NMEA messages.
• Radar Cursor Tracking, which is implemented using the NMEA Radar System Data (RSD)
sentence format
• Slew to Waypoint, which uses the NMEA Bearing and Distance to Waypoint, Great Circle
(BWC) sentence format
• Radar Tracking, which uses the NMEA Tracked Target Message (TTM) sentence format
Even though you can only choose three types of messages to enable through the NMEA interface,
the M400 uses additional messages to perform the calculations needed to respond to these three.
If your system is not responding as expected, verify that the NMEA device sending messages is
sending the following additional message types:
• HDT Heading, True
• GGA Global Positioning System Fix Data
• VHW Water Speed and Heading
• OSD Own Ship Data
• TLL Target Latitude and Longitude
Any combination or all three messages can be enabled; when more than one type is enabled, the
system processes RSD first, then BWC, and finally TTM. For example, if the unit is listening to
BWC or TTM messages and looking at a particular target and it receives an RSD message, it waits
until the end of the dwell time and then move on to the RSD message, ignoring all other input.
Note:
Using the joystick to pan or tilt the camera always takes priority over processing of an
NMEA message.
Each message type has a unique icon associated with it. Depending on the Icon Display Mode,
these icons either always display or display momentarily when a message is received. In both
cases, they flash on and off when the message is received.
Additional settings such as target dwell time affect how the messages are processed. Dwell time
determines how long the camera remains on a particular target. The ability of the M400 to
accurately track a target depends on the quality of the data sent from the radar unit.
The ability of the radar to effectively track a target is influenced by several factors, such as the
make and model of the radar unit, the radar update rate, the relative angular rate of the target, the
angular rate of the boat heading and the velocity of the target being tracked.
Note:
It is important to enter the accurate offset location of the camera above the water line to
ensure the unit’s pointing accuracy for close-in targets. Refer to the
M400 Installation Guide
.
While you can choose to track a large number of targets, in practical terms the number of targets is
linked to the dwell time. Since the camera looks at each target for a minimum of 10 seconds before
moving on to the next target, when the number of targets become too large, the system will take
too long to cycle through them all for the information to be of any real use.
www.
.com
information@itm.com
1.800.561.8187
