NMEA 0183

Le standard NMEA-0183 est un format texte de messages structurant des données produites (essentiellement) par des récepteurs GPS via une liaison série (Baud rate: 4800 Number of data bits: 8 (bit 7 is 0) Stop bits: 1 (or more) Parity: none Handshake: none). NMEA-0183 est un format de données textuel des relevés GPS acquis par les terminaux GPS puis retournés à un hôte (par un port série par exemple). Il couvre un large spectre de données de navigation. Ces données sont envoyées par le récepteur en mode heartbeat à fréquence fixe (0,5 Hz par exemple).

Format
Documentation http://www.sparkfun.com/datasheets/GPS/NMEA%20Reference%20Manual1.pdf

Syntaxe
Chaque message est structuré de la manière suivante :

$AABBB,CC,DD,...*CK

$ marqueur de début du message AA pour l'identifiant de l'émetteur (talker) BBB pour la phrase (sentence) CK Checksum  Carriage Return \r  Line Feed \n

le code C de la fonction de checksum uchar calcChecksum(uchar checksum, uchar c){ if ( c == '$' ) return 0; if ( c != '\r' &&  c != '\n'  &&  c != '*' ) { checksum ^= c;       } return checksum; }
 * 1) define uchar unsigned char

le code Arduino de la fonction de checksum byte calcChecksum(byte checksum, byte c){ if ( c == '$' ) return 0; if ( c != '\r' &&  c != '\n'  &&  c != '*' ) { checksum ^= c; } return checksum; }

byte calcChecksumBuf(byte checksum, byte buf[], int i, int len){ for(i<len; i++){ checksum=calcChecksum(checksum,buf[i]); } return checksum; }

Liens

 * http://www.tronico.fi/OH6NT/docs/NMEA0183.pdf

Messages de sortie
Chaque message est une ligne de texte commencant par $ et se terminant par [CR][LF] et contient les champs suivants $IDMSG,D1,D2,D3,...Dn*CS[CR][LF] ID: Talker id (GP pour GPS) MSG: Message id Di: Msg data fields CS: Ckecksum 2 hexa for 8 bits

Most common message Ids are
 * GGA : GPS fix data (NMEA Version 2.1)
 * GLL : Geographic position - Latitude/Longitude
 * GSA : GPS DOP and active satellites
 * GSV : GPS satellites in view
 * RMC : Recommended minimum specific GPS/Transit data
 * VTG : Track made good and ground speed
 * ZDA : SiRF Timing Message
 * MSS : MSK Receiver Signal
 * 150 : OkToSend

Exemples $GPGGA,164503.0,4511.636,N,00546.242,E,1,6,3.25,00220,M,048,M,,*66 $GPVTG,000.0,T,002.0,M,000.00,N,000.00,K*4C $GPRMC,214434,A,3753.666,N,12203.162,W,0.0,0.0,270901,15.4,E,A*33 $GPGGA,214616,3753.667,N,12203.167,W,1,04,5.6,121.1,M,-27.4,M,,*79 $GPGSV,3,1,10,01,69,062,47,03,12,106,37,04,12,279,00,08,12,250,00*77 $GPGLL,3753.667,N,12203.167,W,214616,A,A*54 $GPBOD,,T,,M,,*47

Messages d'entrée
$IDMSG,D1,D2,D3,...Dn*CS[CR][LF]

ID=PSRF

MSG=
 * 100 : SetSerialPort : Set PORT A parameters and protocol
 * 101 : NavigationInitialization : Parameters required for start using X/Y/Z (Input coordinates must be WGS84)
 * 102 : SetDGPSPort = Set PORT B parameters for DGPS input
 * 103 : Query/Rate Control = Query standard NMEA message and/or set output rate
 * 104 : LLANavigationInitialization = Parameters required for start using Lat/Lon/Alt (Input coordinates must be WGS84)
 * 105 : Development Data On/Off = Development Data messages On/Off
 * 106 : Select Datum = Selection of datum to be used for coordinate transformations.
 * MSK : MSK Receiver Interface = Command message to a MSK radio-beacon receiver.

Message GLL - Geographic Position - Latitude/Longitude
contains the latitude and longitude of the present vessel position, the time of the position fix and the status. $GPGLL,llll.lll,a,yyyyy.yyy,a,hhmmss.s,A*hh[CR][LF]
 * 1,2 Latitude, N (North) or S (South)
 * 3,4 Longitude, E (East) or W (West)
 * 5 UTC of position
 * 6 Status: A = Valid, V= Invalid
 * hh Checksum

Message GGA - GPS Fix Data
includes time, position and fix related data for the GPS receiver. $GPGGA,hhmmss,llll.lll,a,nnnnn.nnn,b,t,uu,v.v,w.w,M,x.x,M,y.y,zzzz*hh[CR][LF]
 * 1 UTC of Position
 * 2,3 Latitude, N (North) or S (South)
 * 4,5 Longitude, E (East) or W (West)
 * 6 GPS Quality Indicator: 0 = No GPS, 1 = GPS, 2 = DGPS
 * 7 Number of Satellites in Use
 * 8 Horizontal Dilution of Precision (HDOP)
 * 9, 10 Antenna Altitude in Meters, M = Meters
 * 11, 12 Geoidal Separation in Meters, M=Meters. Geoidal separation is the difference between the WGS-84 earth ellipsoid and mean-sea-level.
 * 13 Age of Differential GPS Data. Time in seconds since the last Type 1 or 9 Update
 * 14 Differential Reference Station ID (0000 to 1023)
 * hh Checksum

Message VTG - Track Made Good and Ground Speed
conveys the actual track made good (COG) and the speed relative to the ground (SOG). $GPVTG,x.x,T,x.x,M,x.x,N,x.x,K*hh[CR][LF] Remark: Velocity is always described as horizontal speed and heading
 * 1 Track made good in degrees true.
 * 2 Track made good in degrees magnetic.
 * 3,4 Speed over the ground (SOG) in knots.
 * 5,6 Speed over the ground (SOG) in kilometer per hour.
 * hh Checksum

Mac OS X
Ligne de commande screen /dev/tty.usbserial 4800

Linux
awk -F, '/\$GPGGA/ {print strftime("%Y-%m-%d "),  $2, (substr($3,0,2) + (substr($3,3) / 60.0)) $4,  (substr($5,0,3) + (substr($5,4) / 60.0)) $6, $10; fflush;}' /dev/tty.usbserial

GPSLabel

GPSD

Arduino

 * http://arduiniana.org/libraries/TinyGPS/
 * http://www.maartenlamers.com/nmea/

Java avec RXTX

 * http://gpsmap.sourceforge.net
 * http://javagps.sourceforge.net

Pour en savoir plus

 * http://vancouver-webpages.com/peter/idx_faq.html
 * http://home.mira.net/~gnb/gps/nmea.html
 * http://www.grc.nasa.gov/WWW/MAEL/ag/agnmea1.htm