- Source: NMEA 0183
NMEA 0183 is a combined electrical and data specification for communication between marine electronics such as echo sounder, sonars, anemometer, gyrocompass, autopilot, GPS receivers and many other types of instruments. It has been defined and is controlled by the National Marine Electronics Association (NMEA). It replaces the earlier NMEA 0180 and NMEA 0182 standards. In leisure marine applications, it is slowly being phased out in favor of the newer NMEA 2000 standard, though NMEA 0183 remains the norm in commercial shipping.
Details
The electrical standard that is used is EIA-422, also known as RS-422, although most hardware with NMEA-0183 outputs are also able to drive a single EIA-232 port. The standard calls for optically isolated inputs. There is no requirement for isolation for the outputs.
The NMEA 0183 standard uses a simple ASCII, serial communications protocol that defines how data are transmitted in a "sentence" from one "talker" to multiple "listeners" at a time. Through the use of intermediate expanders, a talker can have a unidirectional conversation with a nearly unlimited number of listeners, and using multiplexers, multiple sensors can talk to a single computer port.
At the application layer, the standard also defines the contents of each sentence (message) type, so that all listeners can parse messages accurately.
While NMEA 0183 only defines an RS-422 transport, there also exists a de facto standard in which the sentences from NMEA 0183 are placed in UDP datagrams (one sentence per packet) and sent over an IP network.
The NMEA standard is proprietary and sells for at least US$2000 (except for members of the NMEA) as of September 2020. However, much of it has been reverse-engineered from public sources.
UART settings
There is a variation of the standard called NMEA-0183HS that specifies a baud rate of 38,400. This is in general use by AIS devices.
Message structure
All transmitted data are printable ASCII characters between 0x20 (space) to 0x7e (~)
Data characters are all the above characters except the reserved characters (See next line)
Reserved characters are used by NMEA0183 for the following uses:
Messages have a maximum length of 82 characters, including the $ or ! starting character and the ending
The start character for each message can be either a $ (For conventional field delimited messages) or ! (for messages that have special encapsulation in them)
The next five characters identify the talker (two characters) and the type of message (three characters).
All data fields that follow are comma-delimited.
Where data is unavailable, the corresponding field remains blank (it contains no character before the next delimiter – see Sample file section below).
The first character that immediately follows the last data field character is an asterisk, but it is only included if a checksum is supplied.
The asterisk is immediately followed by a checksum represented as a two-digit hexadecimal number. The checksum is the bitwise exclusive OR of ASCII codes of all characters between the $ and *, not inclusive. According to the official specification, the checksum is optional for most data sentences, but is compulsory for RMA, RMB, and RMC (among others).
As an example, a waypoint arrival alarm has the form:
$GPAAM,A,A,0.10,N,WPTNME*32
Another example for AIS messages is:
!AIVDM,1,1,,A,14eG;o@034o8sd
NMEA sentence format
The main talker ID includes:
BD or GB - Beidou
GA - Galileo
GP - GPS
GL - GLONASS.
NMEA message mainly include the following "sentences" in the NMEA message:
One example, the sentence for Global Positioning System Fixed Data for GPS should be "$GPGGA".
Vendor extensions
Most GPS manufacturers include special messages in addition to the standard NMEA set in their products for maintenance and diagnostics purposes. Extended messages begin with "$P". These extended messages are not standardized.
Software compatibility
NMEA 0183 is supported by various navigation and mapping software. Notable applications include:
Infrakit SURVEY
DeLorme Street Atlas
ESRI
Google Earth
Google Maps Mobile Edition
gpsd - Unix GPS Daemon
JOSM - OpenStreetMap Map Editor
MapKing
Microsoft MapPoint
Microsoft Streets & Trips
NetStumbler
OpenCPN - Open source navigation software
OpenBSD's hw.sensors framework with the nmea(4) pseudo-device driver
OpenNTPD through sysctl hw.sensors § timedelta API
Rand McNally StreetFinder
ObserVIEW
QGIS
Sample file
A sample file produced by a Tripmate 850 GPS logger. This file was produced in Leixlip, County Kildare, Ireland. The record lasts two seconds.
$GPGGA,092750.000,5321.6802,N,00630.3372,W,1,8,1.03,61.7,M,55.2,M,,*76
$GPGSA,A,3,10,07,05,02,29,04,08,13,,,,,1.72,1.03,1.38*0A
$GPGSV,3,1,11,10,63,137,17,07,61,098,15,05,59,290,20,08,54,157,30*70
$GPGSV,3,2,11,02,39,223,19,13,28,070,17,26,23,252,,04,14,186,14*79
$GPGSV,3,3,11,29,09,301,24,16,09,020,,36,,,*76
$GPRMC,092750.000,A,5321.6802,N,00630.3372,W,0.02,31.66,280511,,,A*43
$GPGGA,092751.000,5321.6802,N,00630.3371,W,1,8,1.03,61.7,M,55.3,M,,*75
$GPGSA,A,3,10,07,05,02,29,04,08,13,,,,,1.72,1.03,1.38*0A
$GPGSV,3,1,11,10,63,137,17,07,61,098,15,05,59,290,20,08,54,157,30*70
$GPGSV,3,2,11,02,39,223,16,13,28,070,17,26,23,252,,04,14,186,15*77
$GPGSV,3,3,11,29,09,301,24,16,09,020,,36,,,*76
$GPRMC,092751.000,A,5321.6802,N,00630.3371,W,0.06,31.66,280511,,,A*45
Note some blank fields, for example:
GSV records, which describe satellites 'visible', lack the SNR (signal–to–noise ratio) field for satellite 16 and all data for satellite 36.
GSA record, which lists satellites used for determining a fix (position) and gives a DOP of the fix, contains 12 fields for satellites' numbers, but only 8 satellites were taken into account—so 4 fields remain blank.
Status
NMEA 0183 continued to be maintained separately: V4.10 was published in early May 2012, and an erratum noted on 12 May 2012.
On November 27, 2018, it was issued an update to version 4.11, which supports Global Navigation Satellite Systems other than GPS.
See also
GPS Exchange Format
TransducerML
IEEE 1451
IEC 61162
NMEA 2000
NMEA OneNet
RTCM SC-104
RINEX
References
External links
National Marine Electronics Association
NMEA's website about NMEA 0183
NMEA Specifications at APRS Info
Kata Kunci Pencarian:
- JOSM
- GPSBabel
- NMEA 0183
- NMEA 2000
- National Marine Electronics Association
- Automatic identification system
- GPS Exchange Format
- Marine electronics
- Time server
- OpenCPN
- IEC 61162
- Transistor–transistor logic
