NMEA is a standard protocol, used by GPS receivers to transmit data. NMEA output is EIA-422A but for most purposes you can consider it RS-232 compatible. Use 4800 BPS, 8 data bits, no parity and one stop bit (8N1). NMEA 0183 sentences are all ASCII. Each sentence begins with a dollar sign ($) and ends with a carriage return linefeed (<CR><LF>). Data is comma delimited. All commas must be included as they act as markers. Some GPS do not send some of the fields. A checksum is optionally added (in a few cases it is mandatory). Following the $ is the address field aaccc. aa is the device ID. GP is used to identify GPS data. Transmission of the device ID is usually optional. ccc is the sentence formatter, otherwise known as the sentence name. BRIDGE reads the following sentences.
NMEA 0183 Signals
The following is a list of NMEA messages supported by the Marimsys BRIDGE system:
$IIDBT,6,f,1,mt,1,F <CR><LF> (Depth below Transducer)
1 = depth
2 = foot
3 = depth
4 = meter
5 = fathoms
6 = depth
GGA = Global Positioning System Fix Data
1 = UTC of Position
2 = Latitude
3 = N or S
4 = Longitude
5 = E or W
6 = GPS quality indicator (0=invalid; 1=GPS fix; 2=Diff. GPS fix)
7 = Number of satellites in use [not those in view]
8 = Horizontal dilution of position
9 = Antenna altitude above/below mean sea level (geoid)
10 = Meters (Antenna height unit)
11 = Geoidal separation (Diff. between WGS-84 earth ellipsoid and mean sea level. -=geoid is below WGS-84 ellipsoid)
12 = Meters (Units of geoidal separation)
13 = Age in seconds since last update from diff. reference station
14 = Diff. reference station ID#
15 = Checksum
GSA = GPS receiver operating mode, SVs used for navigation, and DOP values.
1 = Mode:M =Manual, forced to operate in 2D or 3D A =Automatic, 3D/2D
2 = Mode:
1 =Fix not available
3-14 = IDs of SVs used in position fix (null for unused fields)
15 = PDOP
16 = HDOP
17 = VDOP
GSV = Number of SVs in view, PRN numbers, elevation, azimuth & SNR values.
1 = Total number of messages of this type in this cycle
2 = Message number
3 = Total number of SVs in view
4 = SV PRN number
5 = Elevation in degrees, 90 maximum
6 = Azimuth, degrees from true north, 000 to 359
7 = SNR, 00-99 dB (null when not tracking)
8-11 = Information about second SV, same as field 4-7
12-15 = Information about third SV, same as field 4-7
16-19 = Information about fourth SV, same as field 4-7
$IIHSC17,C,38,m <CR><LF> (Temperature Submerged - Celsius)
1 = temperature
2 = temperature character
3 = depth of reading
4 = meters
$IIMTW,17,c<CR><LF> Mean Temperature of Water
1 = temperature : string[ 5 ];
2 = Celsius : char;
RMA = Navigation data from present position
1 = Data status
2 = Latitude
3 = N/S
4 = longitude
5 = W/E
6 = not used
7 = not used
8 = Speed over ground in knots
9 = Course over ground
10 = Variation
11 = Direction of variation E/W
12 = Checksum
RMB = Recommended Minimum Navigation Information
1 = Data Status (V=navigation receiver warning)
2 = Crosstrack error in nautical miles
3 = Direction to steer (L or R) to correct error
4 = Origin Waypoint ID#
5 = Destination Waypoint ID#
6 = Destination Waypoint latitude
7 = N or S
8 = Destination Waypoint longitude
9 = E or W
10 = Range to destination in nautical miles
11 = Bearing to destination, degrees True
12 = Destination closing velocity in knots
13 = Arrival status; (A=entered or perpendicular passed)
14 = Checksum
RMC = Recommended Minimum Specific GPS/TRANSIT Data
1 = UTC of position fix
2 = Data status (V=navigation receiver warning)
3 = Latitude of fix
4 = N or S
5 = Longitude of fix
6 = E or W
7 = Speed over ground in knots
8 = Track made good in degrees True
9 = UT date
10 = Magnetic variation degrees (Easterly var. subtracts from true course)
11 = E or W
12 = Checksum
1 = temperature
2 = units of temperature
3 = depth of reading
4 = meters of depth
5 = velocity of knotmeter
6 = knots
7 = velocity of knotmeter
8 = km
VTG = Actual track made good and speed over ground
1 = Track made good
2 = Fixed text ‘T’ indicates that track made good is relative to true north
3 = not used
4 = not used
5 = Speed over ground in knots
6 = Fixed text ‘N’ indicates that speed over ground in knots
7 = Speed over ground in kilometres/hour
8 = Fixed text ‘K’ indicates that speed over ground is in kilometres/hour
9 = Checksum
TPR = Trawl Position Relative Vessel
1 = Horizontal range relative to target
2 = Meters (0 - 4000M)
3 = Bearing to the Target, relative to the vessel heading. Resolution is one degree.
4 = Separator.
5 = Depth of trawl below the surface
6 = Meters (0 - 2,000)
HFB = Trawl Headrope to Footrope and Bottom
1 = Distance from headrope to footrope
2 = Meters (0-100)
3 = Distance from the headrope to bottom
4 = Meters (0-100)
TDS = Trawl Door Spread distance
1 = Distance between trawl doors
2 = Meters (0-300)
TS2 = Trawl Door Spread 2 distance
1 = Second spread distance
2 = Meters
TFI = Catch sensors to represent trawl filling
x = Catch sensor #1 (0 = off, 1 = on, 2 = no answer)
y = Catch sensor #2 (0 = off, 1 = on, 2 = no answer)
z = Catch sensor #3 (0 = off, 1 = on, 2 = no answer)
TPT = Trawl Position True relative to the vessel
1 = Horizontal distance from the vessel center line. Value is positive if trawl is to starboard, negative if the trawl is to port.
2 = Meters
3 = Horizontal distance from the transducer to the trawl along the vessel center line. The value is normally positive assuming the trawl is located behind the vessel.
4 = Meters
5 = Depth of the trawl below the surface. The value is normally positive, assuming the trawl is located below the ocean surface.
6 = Meters
TTM = Tracked target message (ARPA Radar only)
1 = Target number, (00 - 99)
2 = Target distance from own ship
3 = Bearing from own ship
4 = Target bearing is T / R (True / Relative)
5 = Target Speed
6 = Target Course
7 = Target course is T / R (True / Relative)
8 = Distance of Closest Point of Approach (CPA)
9 = Time to CPA in minutes, positive is approaching target, ( - ) negative is moving away.
10 = Speed / Distance units K / N / S (Kilometers / Knots / Statute miles)
11 = User data - generally target name
12 = Target Status L / Q / T (Lost from tracking process / Query - in process of acquisition / Tracking at the present time)
13 = Reference target = R, null otherwise
14 = Time of data in UTC format (hhmmss.ss)
15 = Type of target acquisition A / M (Automatic / Manual)
16 = Checksum
TPT Trawl Position True vessel.
x,M Horizontal range to the target (0 - 4000m).
y,P True bearing to the target (i.e. relative north). The resolution is l degree.
z.z,M Depth of trawl below the surface (0 -2000m).
As with to the TPR message, the difference is the bearing to the trawl.
TPC Trawl Position Cartesian Coordinates.
x Horizontal distance from vessel center line. Value is positive if trawl is on the starboard side, negative on port side.
y Horizontal distance from transducer to trawl in center line direction. Value is normally positive.
z Depth from surface to trawl. Value is normally positive.
GLL Trawl’s Geographical Latitude and Longitude
ddmm.hh,N Latitude Deg.Min.Hundredths N=North, S=South lat.
dddmm.hh,W Longitude Deg.Min.Hundredths,W=West, E=East long.
DBS Depth Below Surface.
x.x Depth in meter (0 - 2000).
The fields for depth in feet and fathoms are empty.
MTW Meteorological Temperature in Water.
xx.x Water temperature (°C) measured at the trawl. (Sign prefix only if minus). Range from -5°C to + 30°C.
C Celsius degrees.
HFB Headrope to Footrope and Bottom.
x.x,M Distance from headrope to footrope (0 - 100m).
y.y,M Distance from headrope to bottom (0 - 100m).
TDS Trawl Door Spread
x.x,M Spread distance in meters (0 - 300m).