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balloon:gpsinfo
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NMEA Data

  • $GPGGA : Essential fix data which provide 3D location and accuracy data.
    • Sentence Form : $GPGGA,hhmmss.sss,ddmm.mmm,a,dddmm.mmm,a,n,nn,x.x,x.x,M,x.x,M,,*hh
      1. $GPGGA : NMEA Format
      2. hhmmss.sss : UTC Time
      3. ddmm.mmm : Latitude
      4. a : N/S(North/South)
      5. dddmm.mmm : Longitude
      6. a : E/W(East/West)
      7. n : Fix quality
        • 0 = invalid
        • 1 = GPS fix (SPS)
        • 2 = DGPS fix
        • 3 = PPS fix
        • 4 = Real Time Kinematic
        • 5 = Float RTK
        • 6 = estimated (dead reckoning) (2.3 feature)
        • 7 = Manual input mode
        • 8 = Simulation mode
      8. nn : Number of satellites being tracked
      9. x.x : Horizontal dilution of position
      10. x.x : Altitude (Unit : meter)
      11. M : Unit of Altitude - meter
      12. x.x : Height of geoid (mean sea level) above WGS84
      13. M : Unit of Geoid - meter
      14. (empty field) : time in seconds since last DGPS update
      15. (empty field) : DGPS station ID number
      16. hh : the checksum data, always begins with *
  • $GPGSA : Overall satellite reception data.
    • Sentence Form : $GPGSA,A,x,xx,xx,xx,xx,xx,xx,xx,xx,xx,xx,xx,xx,x.x,x.x,x.x*hh
      1. $GPGSA : NMEA Format
      2. A : Auto selection of 2D or 3D fix (M = manual)
      3. x : 3D fix - values include:
        • 1 = no fix
        • 2 = 2D fix
        • 3 = 3D fix
      4. xx : PRNs of satellites used for fix (space for 12)
      5. xx : PRNs of satellites used for fix (space for 12)
      6. xx : PRNs of satellites used for fix (space for 12)
      7. xx : PRNs of satellites used for fix (space for 12)
      8. xx : PRNs of satellites used for fix (space for 12)
      9. xx : PRNs of satellites used for fix (space for 12)
      10. xx : PRNs of satellites used for fix (space for 12)
      11. xx : PRNs of satellites used for fix (space for 12)
      12. xx : PRNs of satellites used for fix (space for 12)
      13. xx : PRNs of satellites used for fix (space for 12)
      14. xx : PRNs of satellites used for fix (space for 12)
      15. xx : PRNs of satellites used for fix (space for 12)
      16. x.x : PDOP (dilution of precision)
      17. x.x : Horizontal dilution of precision (HDOP)
      18. x.x : Vertical dilution of precision (VDOP)
      19. hh : the checksum data, always begins with *
  • $GPGSV : Detailed satellite data.(for up to 4 satellites per sentence)
    • Sentence Form : $GPGSV,x,x,xx,xx,xx,xxx,xx,xx,xx,xxx,xx,xx,xx,xxx,xx,xx,xx,xxx,xx*hh
      1. $GPGSA : NMEA Format
      2. x : Number of sentences for full data
      3. x : sentence n of total
      4. xx : Number of satellites in view
      5. xx : Satellite PRN number
      6. xx : Elevation, degrees
      7. xxx : Azimuth, degrees
      8. xx : Number of satellites in view
      9. xx : Satellite PRN number
      10. xx : Elevation, degrees
      11. xxx : Azimuth, degrees
      12. xx : Number of satellites in view
      13. xx : Satellite PRN number
      14. xx : Elevation, degrees
      15. xxx : Azimuth, degrees
      16. xx : Number of satellites in view
      17. xx : Satellite PRN number
      18. xx : Elevation, degrees
      19. xxx : Azimuth, degrees
      20. xx : SNR - higher is better
      21. hh : the checksum data, always begins with *
  Ex)
  $GPGSV,3,1,12,05,54,069,45,12,44,061,44,21,07,184,46,22,78,289,47*72 
  $GPGSV,3,2,12,30,65,118,45,09,12,047,37,18,62,157,47,06,08,144,45*7C 
  $GPGSV,3,3,12,14,39,330,42,01,06,299,38,31,30,256,44,32,36,320,47*7B 
  • $GPRMC : Minimum recommended data.
    • Sentence Form : $GPRMC,hhmmss.sss,A,dddmm.mmmm,a,dddmm.mmmm,a,x.x,x.x,ddmmyy,x.x,a*hh
      1. $GPRMC : NMEA Format
      2. hhmmss.sss : Fix taken at 12:35:19 UTC
      3. A : Status A=active or V=Void.
      4. dddmm.mmmm : Latitude
      5. a : N/S(North/South)
      6. dddmm.mmmm : Longitude
      7. a : E/W(East/West)
      8. x.x : Speed over the ground in knots
      9. x.x : Track angle in degrees True
      10. ddmmyy : UTC Date
      11. x.x : Magnetic Variation
      12. a : Magnetic Variation
      13. hh : the checksum data, always begins with *
  • $GPVTG : Vector track and speed over ground.
    • Sentence Form : GPVTG,x.x,T,x.x,M,x.x,N,x.x,K,a*hh
      1. $GPVTG : NMEA Format
      2. x.x : True track made good (degrees)
      3. T : True track made good (degrees)
      4. x.x : Magnetic track made good
      5. M : Magnetic track made good
      6. x.x : Ground speed, knots
      7. N : Ground speed, knots
      8. x.x : Ground speed, Kilometers per hour
      9. K : Ground speed, Kilometers per hour
      10. hh : the checksum data, always begins with *

- We use $GPGGA for Latitude(#3,#4), Longitude(#5,#6) and Altitude(#10,#11), $GPGSV for number of Satellites(#3) -

GPS Start Types

  • Hot Start
    • The GPS receiver remembers its last calculated position and which satellites were in view, the almanac used, and the UTC Time. It then performs a reset and attempts to acquire satellites and calculate a new position based upon the previous information. This is the quickest re-acquisition of a GPS lock.
  • Warm Start
    • The GPS receiver remembers its last calculated position, almanac used, and knows the UTC Time, but not which satellites were in view. It then performs a reset and attempts to obtain the satellite signals and calculate a new position. The receiver has a general idea of which satellites to look for because it knows its last position and the almanac helps identify which satellites are visible in the sky. This takes longer than a Hot Start but not as long as a Cold Start.
  • Cold Start
    • The GPS receiver dumps all information and resets. It then attempts to locate satellites and then calculate a GPS lock. This takes the longest because there is no known information. The GPS receiver has to attempt to lock a satellite signal from all of the satellites, basically like polling, which takes a lot longer than knowing which satellites to look for. This re-acquisition of a GPS lock takes the longest.
balloon/gpsinfo.txt · Last modified: 2011/12/22 18:12 by gssai