Introduction to GPS Data Introduction to GPS Data

NMEA & RTCMNMEA & RTCM

Donald Donald ChoiChoi, ALS/G2, ALS/G2

Common GPS Data FormatCommon GPS Data FormatRINEX RINEX •• Combine data from different manufacturerCombine data from different manufacturer’’s GPS receiverss GPS receivers•• For static data processing and archive For static data processing and archive

NMEANMEA•• Transmission of data between GPS receiver and other Transmission of data between GPS receiver and other

devices (e.g. GPS antenna devices (e.g. GPS antenna PDA with PDA with ArcPadArcPad software)software)•• For real time positioningFor real time positioning

RTCM RTCM •• Transmission of data between GPS receivers (e.g Base Transmission of data between GPS receivers (e.g Base

Rover)Rover)•• Binary file (more compact but difficult to understand)Binary file (more compact but difficult to understand)•• For real time DGPS/RTK correctionsFor real time DGPS/RTK corrections

Common GPS Data FormatCommon GPS Data Format

NMEA DataNMEA Data

IntroductionIntroductionBackgroundBackground

Message Format and Sentence structuresMessage Format and Sentence structures

Common NMEA sentenceCommon NMEA sentence

Other GPSOther GPS--related NMEA sentencerelated NMEA sentence

ReferencesReferences

Flow of NMEA data between Flow of NMEA data between devicesdevices

NMEA data transfer from GPS antenna to PDA with ArcPADsoftware

Real-time positioning using the NMEA data

NMEA data used in Network RTKNMEA data used in Network RTK

(X,Y,Z,t)

cm position accuracy

(X,Y,Z,t)(X,Y,Z,t)

Fix the Ambiguity

(X,Y,Z,t)

Ref. Stn X,Y,ZPseudo-range + Corrn. Carrier Phase + Corrn.

(X,Y,Z,t)

Real Time Position of Rover

Data CentreNMEA 0183

RTCM SC-104 Ver. 2.1

What is NMEA data?What is NMEA data?

Developed by National Marine Electronics AssociationDeveloped by National Marine Electronics Association

Standard for interfacing marine electronic devices (GPS, Standard for interfacing marine electronic devices (GPS, Compass, Compass, EchosounderEchosounder……))

Standard specifies the electrical signal requirements, Standard specifies the electrical signal requirements, data transmission protocol (i.e. agreed format for data transmission protocol (i.e. agreed format for transmitting data between two devices), message transmitting data between two devices), message formatsformats

Most GPS receivers understand the most popular NMEA Most GPS receivers understand the most popular NMEA format format NMEA 0183NMEA 0183

What is NMEA data?What is NMEA data?

ASCII fileASCII file•• Easily readable (even by people)Easily readable (even by people)•• Less compact than binaryLess compact than binary

Numerous sentence typesNumerous sentence types•• Not all related GPS applicationNot all related GPS application•• Some popular GPSSome popular GPS--related sentences related sentences

are described in this presentationare described in this presentation

NMEA settings NMEA settings

Baud rate: 4800 (Baud rate: 4800 (4800 characters in one 4800 characters in one second )second )Data bits: 8 (Bit 7 set to 0)Data bits: 8 (Bit 7 set to 0)Stop bits: 1 or 2Stop bits: 1 or 2Parity: noneParity: none

The The ““sendsend”” device and device and ““receivereceive”” device device should have same setting so as to transfer should have same setting so as to transfer the NMEA data the NMEA data

Standard Message FormatStandard Message Format

$$aaaaaaaaaa, df1,df2, df1,df2……………… [Carriage Return][Line Feed][Carriage Return][Line Feed]

•• Each message start with $Each message start with $•• Five characters after $ are address fieldFive characters after $ are address field•• Multiple data fields delimited by commasMultiple data fields delimited by commas•• Check sum (optional): a 2Check sum (optional): a 2--character field character field

(0(0--9,A9,A--F) to increase data integrityF) to increase data integrity•• (*) character placed after the last data field(*) character placed after the last data field

Sentence structureSentence structureThere are three sentence structuresThere are three sentence structures

•• Talker: output from talker (e.g. GPS Talker: output from talker (e.g. GPS receiver) to other devices (PAD)receiver) to other devices (PAD)

•• Query: means for listener (e.g. notebook) Query: means for listener (e.g. notebook) to request specified talker sentence from to request specified talker sentence from talker (GPS receiver)talker (GPS receiver)

•• Proprietary: means for manufactures to Proprietary: means for manufactures to use nonuse non--standard sentences for special standard sentences for special purpose purpose

Talker sentenceTalker sentence

Format: $Format: $ttsssttsss, df1, df2, df1, df2……[CR][LF][CR][LF]

•• tttt: defines device (for : defines device (for gpsgps receivers the prefix is GP)receivers the prefix is GP)•• ssssss: sentence type : sentence type

ExampleExample$GPGGA,031956,2218.2035,N,11410.7595,E,1,04,3,9,005.9,M,$GPGGA,031956,2218.2035,N,11410.7595,E,1,04,3,9,005.9,M,--001.3,M,,*51001.3,M,,*51

The talker sends the GPS data in GGA sentence The talker sends the GPS data in GGA sentence format.format.

Query sentenceQuery sentenceFormat: $Format: $ttllQttllQ, , ssssss, [CR][LF], [CR][LF]

ExampleExampleCCGPQ,GGA, [CR][LF]CCGPQ,GGA, [CR][LF]

A computer (CC) is requesting from GPS device A computer (CC) is requesting from GPS device (GP) the GGA sentence(GP) the GGA sentence

Proprietary sentenceProprietary sentenceFormat: $PmmmA,df1,df2,Format: $PmmmA,df1,df2,……..[CR][LF][CR][LF]•• ““PP”” indictesindictes it is a proprietary messageit is a proprietary message•• ““mmmmmm”” define as the manufacturedefine as the manufacture•• The fifth character is a letter (AThe fifth character is a letter (A--Z) defines the specific Z) defines the specific

message typemessage type

ExampleExample$PLEIS,AHT,0,1.90,0*34$PLEIS,AHT,0,1.90,0*34

•• ““LEI" is LEI" is LeicaLeica manufacturermanufacturer•• ““SS”” for set commandfor set command

The message set the antenna height at 1.9m in the The message set the antenna height at 1.9m in the configuration of the internal sensor setting.configuration of the internal sensor setting.

Common NMEACommon NMEA--0183 Sentence0183 SentenceSentence DescriptionSentence Description$GPGGA: Global positioning system fixed data $GPGGA: Global positioning system fixed data $GPGLL: Geographic position $GPGLL: Geographic position -- latitude / longitudelatitude / longitude$GPGSA: GNSS DOP and active satellites$GPGSA: GNSS DOP and active satellites$GPGSV: GNSS satellites in view$GPGSV: GNSS satellites in view$GPRMC: Recommended minimum specific GPS data$GPRMC: Recommended minimum specific GPS data$GPVTG: Course over ground and ground speed$GPVTG: Course over ground and ground speed

To extract information related to surveyed positionTo extract information related to surveyed positionRecord at least one of the 3 sentences: $GPGGA, $GPGLL, Record at least one of the 3 sentences: $GPGGA, $GPGLL,

$GPRMC$GPRMC

GGA Sentence FormatGGA Sentence Format$GPGGA,092204.999,4250.5589,S,14718.5084,E,1,04,24.4,19.7,M,,,,0$GPGGA,092204.999,4250.5589,S,14718.5084,E,1,04,24.4,19.7,M,,,,0000*1F000*1F

FieldField ExampleExample CommentsComments

Sentence IDSentence ID $GPGGA $GPGGA UTC TimeUTC Time 092204.999 092204.999 hhmmss.ssshhmmss.sssLatitude 4250.5589 Latitude 4250.5589 ddmm.mmmmddmm.mmmmN/S Indicator S N = North, SN/S Indicator S N = North, S = South= SouthLongitude 14718.5084 Longitude 14718.5084 dddmm.mmmmdddmm.mmmmE/W Indicator E E = East, W =E/W Indicator E E = East, W = WestWestPosition Fix 1 0 = InvalidPosition Fix 1 0 = Invalid, 1 = Valid SPS, , 1 = Valid SPS,

2 = Va2 = Valid DGPS, 3 = Valid PPSlid DGPS, 3 = Valid PPSSatellites Used 04 Satellites beiSatellites Used 04 Satellites being used (0ng used (0--12)12)HDOP 24.4 Horizontal diHDOP 24.4 Horizontal dilution of precisionlution of precisionAltitude 19.7 Altitude (WGAltitude 19.7 Altitude (WGSS--84 ellipsoid)84 ellipsoid)Altitude Units M M= MetersAltitude Units M M= MetersGeoidGeoid SeparationSeparation GeoidGeoid separation (WGSseparation (WGS--84 ellipsoid)84 ellipsoid)SeperationSeperation UnitsUnits M= MetersM= MetersTime since DGPS Time since DGPS in secondsin secondsDGPS Station ID DGPS Station ID Checksum *1FChecksum *1F always begin with *always begin with *

GGA Sentence Format (2)GGA Sentence Format (2)$GPGGA,092204.999,4250.5589,S,14718.5084,E,$GPGGA,092204.999,4250.5589,S,14718.5084,E,11,04,24.4,19.7,M,,,,0000*1F,04,24.4,19.7,M,,,,0000*1F

Fix quality:Fix quality:•• 0 = invalid 0 = invalid •• 1 = GPS fix (SPS) 1 = GPS fix (SPS) •• 2 = DGPS fix 2 = DGPS fix •• 3 = PPS fix 3 = PPS fix •• 4 = Real Time 4 = Real Time KinematicKinematic•• 5 = Float RTK 5 = Float RTK

GLL Sentence FormatGLL Sentence Format$GPGLL,4250.5589,S,14718.5084,E,092204.999,A*2D$GPGLL,4250.5589,S,14718.5084,E,092204.999,A*2D

FieldField ExampleExample CommentsCommentsID $GPGLLID $GPGLL

Latitude 4250.5589 Latitude 4250.5589 ddmm.mmmmddmm.mmmmN/S Indicator S N = NorN/S Indicator S N = North, S = Southth, S = SouthLongitude 14718.5084 Longitude 14718.5084 dddmm.mmmmdddmm.mmmmE/W Indicator E E = EasE/W Indicator E E = East, W = Westt, W = WestUTC Time 092204.999 UTC Time 092204.999 hhmmss.ssshhmmss.sssStatus A A =Status A A = Valid, V = InvalidValid, V = InvalidChecksum *2DChecksum *2D

GSA Sentence FormatGSA Sentence Format$GPGSA,A,3,01,20,19,13,,,,,,,,,40.4,24.4,32.2*0A $GPGSA,A,3,01,20,19,13,,,,,,,,,40.4,24.4,32.2*0A

FieldField ExampleExample CommentsCommentsSentence ID $GPGSASentence ID $GPGSAMode 1 A A = Auto 2DMode 1 A A = Auto 2D/3D/3D

M = FoM = Forced 2D/3Drced 2D/3DMode 1 3 1 = No fix,Mode 1 3 1 = No fix, 2 = 2D, 3 = 3D2 = 2D, 3 = 3DSatellite used 1 01 Satellite useSatellite used 1 01 Satellite used on channel 1d on channel 1

..

. .

..Satellite used 12 24 Satellite usedSatellite used 12 24 Satellite used on channel 12on channel 12PDOP 2.5 Position diPDOP 2.5 Position dilution of precisionlution of precisionHDOP 1.3 Horizontal diluHDOP 1.3 Horizontal dilution of precisiontion of precisionVDOP 2.1 Vertical diVDOP 2.1 Vertical dilution of precisionlution of precisionChecksum *0AChecksum *0A

GSV Sentence FormatGSV Sentence Format$GPGSV,3,1,10,20,78,331,45,01,59,235,47,22,41,069,,13,32,252,45*$GPGSV,3,1,10,20,78,331,45,01,59,235,47,22,41,069,,13,32,252,45*7070

FieldField ExampleExample CommentsCommentsSentence ID $GPGSVSentence ID $GPGSVNo. of messages 3 No. of messages inNo. of messages 3 No. of messages in complete (1complete (1--3)3)Sequence no. 1 Sequence no. of tSequence no. 1 Sequence no. of this entry (1his entry (1--3)3)Satellites in view 10Satellites in view 10Satellite ID 1 20 Range is 1Satellite ID 1 20 Range is 1--3232Elevation 1 78 Elevation in deElevation 1 78 Elevation in degrees grees Azimuth 1 331 Azimuth in degreAzimuth 1 331 Azimuth in degrees es SNR 1 45 Signal to noisSNR 1 45 Signal to noise ratio e ratio dBHZdBHZ (0(0--99)99)Satellite ID 2 01 Range is 1Satellite ID 2 01 Range is 1--3232Elevation 2 59 Elevation in deElevation 2 59 Elevation in degrees grees Azimuth 2 235 Azimuth in degreAzimuth 2 235 Azimuth in degreeses

..

..Checksum *70Checksum *70

RMC Sentence FormatRMC Sentence Format$GPRMC,092204.999,A,4250.5589,S,14718.5084,E,0.00,89.68,211200,,$GPRMC,092204.999,A,4250.5589,S,14718.5084,E,0.00,89.68,211200,,*25 *25

FieldField ExampleExample CommentsCommentsSentence ID $GPRMCSentence ID $GPRMCUTC Time 092204.999 UTC Time 092204.999 hhmmss.ssshhmmss.sssStatus A A = ValStatus A A = Valid, V = Invalidid, V = InvalidLatitude 4250.5589 Latitude 4250.5589 ddmm.mmmmddmm.mmmmN/S Indicator S N = North,N/S Indicator S N = North, S = SouthS = SouthLongitude 14718.5084 Longitude 14718.5084 dddmm.mmmmdddmm.mmmmE/W Indicator E E = East, E/W Indicator E E = East, W = WestW = WestSpeed over ground 0.00 KnotsSpeed over ground 0.00 KnotsCourse over ground 0.00 DegreesCourse over ground 0.00 DegreesUTC Date 211200 DDMMYYUTC Date 211200 DDMMYYMagnetic variationMagnetic variation DegreesDegreesMagnetic variation Magnetic variation E = East, W = WestE = East, W = WestChecksum *25Checksum *25

VTG Sentence FormatVTG Sentence Format$GPVTG,89.68,T,,M,0.00,N,0.0,K*5F$GPVTG,89.68,T,,M,0.00,N,0.0,K*5F

FieldField ExampleExample CommentsCommentsSentence ID $GPVTGSentence ID $GPVTGCourse 89.68 Course in Course 89.68 Course in degreesdegreesReference 89.68 T = True heReference 89.68 T = True headingadingCourseCourse Course in degCourse in degreesreesReference 89.68 M = MagnetiReference 89.68 M = Magnetic headingc headingSpeed 0.00 HorizontaSpeed 0.00 Horizontal speedl speedUnits N N = KnUnits N N = KnotsotsSpeed 0.00 HorizontaSpeed 0.00 Horizontal speedl speedUnits K K = KMUnits K K = KM/h/h

Checksum *5FChecksum *5F

NMEANMEA--0183 data file0183 data file

Other GPS NMEA sentences Other GPS NMEA sentences

Sentence DescriptionSentence Description$GPALM: GPS almanac data$GPALM: GPS almanac data$GPGRS: GPS range residuals$GPGRS: GPS range residuals$GPGST: GPS $GPGST: GPS pseudorangepseudorange noise statisticsnoise statistics$GPMSS: Beacon receiver status$GPMSS: Beacon receiver status$GPZDA: UTC and local date/time data$GPZDA: UTC and local date/time data

ReferencesReferences

Common NMEA Common NMEA SetenceSetence types types •• http://www.commlinx.com.au/NMEA_sentences.htmhttp://www.commlinx.com.au/NMEA_sentences.htm

NMEA dataNMEA data•• http://http://www.gpsinformation.org/dale/nmea.htmwww.gpsinformation.org/dale/nmea.htm

The National Marine Electronics The National Marine Electronics AssociationAssociation•• http://http://www.nmea.orgwww.nmea.org//

Common GPS Data FormatCommon GPS Data Format

RTCM correctionRTCM correction

OutlineOutline

BackgroundBackgroundRTCM Data FormatRTCM Data FormatRTCM Message TypesRTCM Message TypesTransmission method of RTCM dataTransmission method of RTCM dataRTCM data used in NetworkRTCM data used in Network--RTKRTK

RTCM correction used in Network RTKRTCM correction used in Network RTK

(X,Y,Z,t)

cm position accuracy

(X,Y,Z,t)(X,Y,Z,t)

Fix the Ambiguity

(X,Y,Z,t)

Ref. Stn X,Y,ZPseudo-range + Corrn. Carrier Phase + Corrn.

(X,Y,Z,t)

Real Time Position of Rover

Data CentreNMEA 0183

RTCM SC-104 Ver. 2.1

KauKau Yi Yi ChauChau DGPS DGPS SevicesSevices•• Radio transmissionRadio transmission•• The corrections are formatted to RTCM 2.0 The corrections are formatted to RTCM 2.0

and broadcast via Radio antennaand broadcast via Radio antenna

RTCM SC-104 V.2.0

RTCM correction used in DGPS serviceRTCM correction used in DGPS service

What is RTCM SCWhat is RTCM SC--104 data?104 data?

Developed by Radio Technical Commission for Developed by Radio Technical Commission for Maritime Services (RTCM)Maritime Services (RTCM)

RTCM organization consists of various special RTCM organization consists of various special committees to develop international standards for committees to develop international standards for maritime maritime radionavigationradionavigation and and radiocommunicationradiocommunicationsystemssystems

RTCM Special Committee (SC) 104 is the one RTCM Special Committee (SC) 104 is the one concerned Differential Global Navigation Satellite concerned Differential Global Navigation Satellite System (DGNSS)System (DGNSS)

RTCM data format related to GPS applications is RTCM data format related to GPS applications is called RTCM SCcalled RTCM SC--104 104

What is RTCM SCWhat is RTCM SC--104 data?104 data?

Industry standard for Real time differential dataIndustry standard for Real time differential data

Continuous and compact binary Continuous and compact binary datadata goodgood for for realreal--time processingtime processing

Has been different versionsHas been different versions•• RTCM2.0 RTCM2.0 •• RTCM2.1RTCM2.1•• RTCM 2.2RTCM 2.2•• RTCM 2.3RTCM 2.3•• RTCM 3.0RTCM 3.0

RTCM Data FormatRTCM Data Format

A data record contains several message types for A data record contains several message types for various contentsvarious contents•• Message 1, Message2Message 1, Message2……. Message N. Message N

Each message comprises header and bodyEach message comprises header and body•• Header: message type, time, length of message, Header: message type, time, length of message,

•• Body: data for every data typeBody: data for every data type

Each data record may not include every message typeEach data record may not include every message type•• Some send every second (e.g. code corrections)Some send every second (e.g. code corrections)•• Others are sent at interval (e.g. base station coordinates)Others are sent at interval (e.g. base station coordinates)

Features of various RTCM versionsFeatures of various RTCM versionsRTCM 2.0RTCM 2.0•• for DGPS applications only (message 1,9) and no RTK datafor DGPS applications only (message 1,9) and no RTK data

RTCM 2.1RTCM 2.1•• retain the full content of RTCM 2.0retain the full content of RTCM 2.0•• add new messages for carrier phase data and RTK add new messages for carrier phase data and RTK

correctionscorrections

RTCM 2.2RTCM 2.2•• contain GLONASS data and associated informationcontain GLONASS data and associated information•• store in newly added messages 31store in newly added messages 31--3636

RTCM 2.3RTCM 2.3•• antenna types (message 23)antenna types (message 23)•• ARP information (message 24)ARP information (message 24)

RTCM 3.0RTCM 3.0•• RTCM 2.3 requires 4800 bps to broadcast dualRTCM 2.3 requires 4800 bps to broadcast dual--frequency frequency

code and carriercode and carrier--phase observation corrections of 12 phase observation corrections of 12 satellites. The information content is send with 1800 bps in satellites. The information content is send with 1800 bps in RTCM 3.0 RTCM 3.0

•• accommodate for new GNSS systems that are under accommodate for new GNSS systems that are under development (e g Galileo)development (e g Galileo)

RTCM Message TypesRTCM Message Types

RTCM Message TypesRTCM Message Types

New messages

added in RTCM2.1

New messages

added in RTCM2.2

New messages

added in RTCM2.3

RTCM Message TypesRTCM Message Types

New messages

added in RTCM2.3

RTCM 3.0 Messages TypeRTCM 3.0 Messages Type

RTCM Raw DataRTCM Raw Data

RTCM Message Type 1RTCM Message Type 1

RTCM Message Type 2RTCM Message Type 2

RTCM Message Type 3+22RTCM Message Type 3+22

RTCM Message 20RTCM Message 20

RTCM Message Type 21RTCM Message Type 21

Transmission method of Transmission method of RealReal--time RTCM datatime RTCM data

Global System for Mobile Communication (GSM)Global System for Mobile Communication (GSM)•• GSM modem and SIM card with service availableGSM modem and SIM card with service available•• Charged by connection timeCharged by connection time

General Packet Radio Service (GPRS)General Packet Radio Service (GPRS)•• An upgrade to GSMAn upgrade to GSM•• Bridging the mobile network to IP networkBridging the mobile network to IP network•• Charged by the amount of download data but not Charged by the amount of download data but not

the connection timethe connection time•• Cheaper than GSMCheaper than GSM

Latency of DGPS and RTK correctionLatency of DGPS and RTK correction

ReferencesReferencesDGPS Data Formats 2.0DGPS Data Formats 2.0•• www.geopp.de/download/DGPSwww.geopp.de/download/DGPS--datadata--formatsformats2.pdf 2.pdf

RTCM recommended standards for RTCM recommended standards for differential NAVSTAR GPS service differential NAVSTAR GPS service www.navcen.uscg.gov/pubs/dgps/rctm104/Default.htmwww.navcen.uscg.gov/pubs/dgps/rctm104/Default.htm

RTCM Official Website RTCM Official Website http://www.rtcm.org/http://www.rtcm.org/

Reference Station Network Reference Station Network Information Distribution Information Distribution http://www.networkhttp://www.network--rtk.info/euler/euler.htmlrtk.info/euler/euler.html

The EndThe EndThank you!Thank you!