1 / 20

Introduction to GPS Data Communications-- NMEA and RTCM

Introduction to GPS Data Communications-- NMEA and RTCM . CHOI Chun-ting, ALS/G2. June 2006. Overview . RINEX Raw GPS static data format for data processing and archive NMEA Standard related to data communication between marine electronics devices.

socorro
Download Presentation

Introduction to GPS Data Communications-- NMEA and RTCM

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Introduction to GPS Data Communications-- NMEA and RTCM CHOI Chun-ting, ALS/G2 June2006

  2. Overview • RINEX • Raw GPS static data format for data processing and archive • NMEA • Standard related to data communication between marine electronics devices. • Transmission of GPS position from GPS receiver to other devices (e.g. GPS receiver to PDA) • For real time positioning • RTCM SC-104 • Transmission of GPS correction from GPS reference station to GPS Rover • For DGPS/RTK surveys

  3. (National Marine Electronics Association) NMEA Data Format

  4. Outline • Example of using NMEA Data Format • About NMEA • Message Format and Sentence Structure • Common NMEA Messages

  5. NMEA using in real-time navigation Real-time positioning Surveyed position NMEA data format GPS receiver ArcPAD software

  6. About NMEA

  7. National Marine Electronics Association • Developed by National Marine Electronics Association • Standard related to the marine electronics devices (GPS, echosounder, …) • Standard specifies the message formats for data transmission between marine electronics devices

  8. What is NMEA ? • NMEA data format contains many various message types • Not all messages related to GPS application. • Even GPS-related messages, there are over 20 various types. • For a GPS survey, only some messages are selected.

  9. NMEA Standard Message Format

  10. Standard Message Format • $aaaaa, df1,df2………[Carriage Return][Line Feed] • Each message start with $ • Five characters after $ are address field • Multiple data fields delimited by commas • Up to 82 characters per each sentence

  11. NMEA Sentence Structure

  12. Sentence structure • There are three sentence structures • Talker: data from GPS receiver to other devices. • Query: “receive” device (e.g. notebook) send query sentence to GPS receiver for specified messages. • Proprietary: non-standard sentence developed by GPS manufacturers for special purposes.

  13. Talker sentence • Format: $ttsss, df1, df2…[CR][LF] • tt: defines device (GPS receivers the prefix is GP) • sss: message type Example $GPGGA,031956,2218.2035,N,11410.7595,E,1,04,3,9,005.9,M,-001.3,M,,*51 • The GPS receiver sends the data in GGA sentence format.

  14. Common NMEA Messages

  15. Common NMEA Messages Position Data Messages $GPGGA: Global positioning system fixed data $GPGLL: Geographic position - latitude / longitude $GPRMC: Recommended minimum specific GPS data Associated Data Messages $GPGSA: GNSS DOP and active satellites $GPGSV: GNSS satellites in view $GPVTG: Course over ground and ground speed .

  16. GGA Message Format $GPGGA,092204.999,4250.5589,S,14718.5084,E,1,04,24.4,19.7,M,,,,0000*1F Field Example Comments Message ID $GPGGA UTC Time 092204.999 hhmmss.sss Latitude 4250.5589 ddmm.mmmm N/S Indicator S N = North, S = South Longitude 14718.5084 dddmm.mmmm E/W Indicator E E = East, W = West Position Fix 1 0 = Invalid, 1 = Valid SPS, 2 = Valid DGPS, 3 = Valid PPS Satellites Used 04 Satellites being used HDOP 24.4 Horizontal dilution of precision Altitude 19.7 Altitude (WGS-84 ellipsoid) Altitude Units M M= Meters Geoid Separation Geoid separation Separation Units M= Meters Time since DGPS in seconds DGPS Station ID Checksum *1F always begin with *

  17. GSV Message Format(satellite in view) $GPGSV,3,1,10,20,78,331,45,01,59,235,47,22,41,069,,13,32,252,45*70 Field Example Comments Sentence ID $GPGSV No. of sentence 3 No. of messages in complete (1-3) Sequence no. 1 Sequence no. of this entry (1-3) Satellites in view 10 Satellite ID 1 20 Range is 1-32 Elevation 1 78 Elevation in degrees Azimuth 1 331 Azimuth in degrees SNR 1 45 Signal to noise ratio dBHZ (0-99) Satellite ID 2 01 Range is 1-32 Elevation 2 59 Elevation in degrees Azimuth 2 235 Azimuth in degrees . . Checksum *70

  18. First epoch Second epoch Sample NMEA data file(output GGA, GSA, GSV and RMC messages)

  19. References • The National Marine Electronics Association http://www.nmea.org/ • Common NMEA Sentence types http://www.commlinx.com.au/NMEA_sentences.htm • NMEA Data Format http://www.gpsinformation.org/dale/nmea.htm

  20. The EndThank you!

More Related