$PGGGA and NMEA standard

Discussion in 'Global Navigation Satellite Systems' started by Henryk Birecki, Feb 3, 2005.

  1. Can anyone tell me how exactly the $GPGGA sentence is defined in NMEA
    standard. Specifically which altitude is it supposed to report? MSL or
    height over ellipsoid? Currently there are devices on the market that
    do both. Garmin and some others reports MSL altitude, SiRF chipset
    devices - altitude over ellipsoid.

    Thanks.

    Henryk Birecki
     
    Henryk Birecki, Feb 3, 2005
    #1
    1. Advertisements

  2. Henryk Birecki

    RumJungle Guest

    RumJungle, Feb 3, 2005
    #2
    1. Advertisements

  3. "Henryk Birecki" <> kirjoitti viestissä
    news:...
    > Can anyone tell me how exactly the $GPGGA sentence is defined in NMEA
    > standard. Specifically which altitude is it supposed to report? MSL or
    > height over ellipsoid? Currently there are devices on the market that
    > do both. Garmin and some others reports MSL altitude, SiRF chipset
    > devices - altitude over ellipsoid.
    >
    > Thanks.
    >
    > Henryk Birecki


    According to the specifications I have been using, you should get both
    height above MSL and WGS84 geoid height.
    The height above (WGS84) ellipsoid is the sum of those two.

    Height above ellipsoid = Altitude above MSL (field 9) + WGS84 geoid height
    (field 11)

    ' $GPGGA - Global Positioning System Fix Data
    ' $GPGGA,155537,6006.718,N,02426.290,E,1,05,2.4,50.5,M,19.7,M,,*79
    ' 1 123519 Fix taken at 12:35:19 UTC
    ' 2,3 4807.038,N Latitude 48 deg 07.038' N
    ' 4,5 01131.324,E Longitude 11 deg 31.324' E
    ' 6 1 Fix quality: 0 = invalid
    ' 1 = GPS fix
    ' 2 = DGPS fix
    ' 7 08 Number of satellites being tracked
    ' 8 0.9 Horizontal dilution of position
    ' 9,11 545.4,M Altitude, Metres, above mean sea level
    ' 11,13 46.9,M Height of geoid (mean sea level) above WGS84 ellipsoid
    ' 13 (empty field) time in seconds since last DGPS update
    ' 14 (empty field) DGPS station ID number

    Eino Uikkanen
    http://www.kolumbus.fi/eino.uikkanen/gb/index.htm
     
    Eino Uikkanen, Feb 3, 2005
    #3
  4. Henryk Birecki

    RumJungle Guest

    Based on the above, this indicates that SiRF is not truly NMEA
    compliant for the GGA message. They have seemed to omit the Height of
    geoid (field 11) and placed the Height above ellipsoid in field 9 where
    this field should be MSL.

    As Dale stated in his web site, the altitude should be suspect if the
    height of geoid is missing.


    Monte---
     
    RumJungle, Feb 3, 2005
    #4
  5. Henryk Birecki

    Sam Wormley Guest

    Henryk Birecki wrote:
    > Can anyone tell me how exactly the $GPGGA sentence is defined in NMEA
    > standard. Specifically which altitude is it supposed to report? MSL or
    > height over ellipsoid? Currently there are devices on the market that
    > do both. Garmin and some others reports MSL altitude, SiRF chipset
    > devices - altitude over ellipsoid.
    >
    > Thanks.
    >
    > Henryk Birecki
    >




    1 2 3 4 5 6 7 8 9 10 11 12 13 14
    ------|---------|--------|-|---------|-|-|--|---|-----|-|----|-|---|---
    "$GPGGA,114114.22,4202.007,N,09339.927,W,2,04,1.5,312.8,M,31.4,M,0.0,04d"

    Where 1 UTC: 11h41m14.22s
    2,3 LAT: 42d02.007m N
    4,5 LONG: 093d39.927m W
    6 GPS: 2 (GPS Quality, 0=invalid, 1=GPS fix, 2=Diff GPS fix)
    7 SATS: 04
    8 HDOP: 1.5
    9,10 ALT: 312.8 meters (1026.25 ft) Orthometric HEight (MSL)
    11,12 GEOID 31.4 meters (Geoidal Separation)
    13 AGE: 0.0 Seconds since last update from diff. ref. station
    14 ID: 04d



    -Sam Wormley
    http://edu-observatory.org/gps/height.html
     
    Sam Wormley, Feb 3, 2005
    #5
  6. Henryk Birecki

    Sam Wormley Guest

    Sam Wormley wrote:
    > Henryk Birecki wrote:
    >
    >> Can anyone tell me how exactly the $GPGGA sentence is defined in NMEA
    >> standard. Specifically which altitude is it supposed to report? MSL or
    >> height over ellipsoid? Currently there are devices on the market that
    >> do both. Garmin and some others reports MSL altitude, SiRF chipset
    >> devices - altitude over ellipsoid.
    >>
    >> Thanks.
    >>
    >> Henryk Birecki
    >>

    >
    >
    >
    > 1 2 3 4 5 6 7 8 9 10 11 12 13 14
    > ------|---------|--------|-|---------|-|-|--|---|-----|-|----|-|---|---
    > "$GPGGA,114114.22,4202.007,N,09339.927,W,2,04,1.5,312.8,M,31.4,M,0.0,04d"
    >
    > Where 1 UTC: 11h41m14.22s
    > 2,3 LAT: 42d02.007m N
    > 4,5 LONG: 093d39.927m W
    > 6 GPS: 2 (GPS Quality, 0=invalid, 1=GPS fix, 2=Diff GPS
    > fix)
    > 7 SATS: 04
    > 8 HDOP: 1.5
    > 9,10 ALT: 312.8 meters (1026.25 ft) Orthometric HEight (MSL)
    > 11,12 GEOID 31.4 meters (Geoidal Separation)
    > 13 AGE: 0.0 Seconds since last update from diff. ref.
    > station
    > 14 ID: 04d
    >
    >
    >
    > -Sam Wormley
    > http://edu-observatory.org/gps/height.html
     
    Sam Wormley, Feb 3, 2005
    #6
  7. If the message includes the Geoid difference data then the altitude is
    referenced to MSL. If the Geoid difference data is missing then the unit
    doesn't have this data and can only report Ellipsoid altitude data.
    Check my web site for a discussion of this.

    Dale

    Henryk Birecki wrote:

    > Can anyone tell me how exactly the $GPGGA sentence is defined in NMEA
    > standard. Specifically which altitude is it supposed to report? MSL or
    > height over ellipsoid? Currently there are devices on the market that
    > do both. Garmin and some others reports MSL altitude, SiRF chipset
    > devices - altitude over ellipsoid.
    >
    > Thanks.
    >
    > Henryk Birecki
    >


    --
    _ _ Dale DePriest
    /`) _ // http://users.cwnet.com/dalede
    o/_/ (_(_X_(` For GPS and GPS/PDAs
     
    Dale DePriest, Feb 3, 2005
    #7
  8. Henryk Birecki

    Hannes Fikis Guest

    Henryk Birecki <> wrote in message news:<>...
    > Can anyone tell me how exactly the $GPGGA sentence is defined in NMEA
    > standard. Specifically which altitude is it supposed to report? MSL or
    > height over ellipsoid? Currently there are devices on the market that
    > do both. Garmin and some others reports MSL altitude, SiRF chipset
    > devices - altitude over ellipsoid.
    >
    > Thanks.
    >
    > Henryk Birecki


    Unfortunately the SIRF chipset (at least V2.32) is not fully compliant
    to $GPGGA.

    Example:
    $GPGGA,143429.726,1122.6419,N,02211.7149,E,0,00,50.0,300.5,M,43.5,M,0.0,0000*40

    If you would get such a message, it would mean that you are 300.5m
    above mean-sea-level and the "geodial separation" (= the difference
    between the WGS-84 earth ellipsoid and mean-sea-level) is 43.5m at
    your position. That is what NMEA specification says.

    But if you use a SRIF-unit, the same message would mean that you are
    262m (=305.5-43.5) above mean-sea-level.

    Not so long ago, SRIF-units couldn´t provide the "geoidal seperation".
    Now they do, but they do that in a way, which is absolutely not NMEA
    compliant.

    Hannes Fikis

    PS: see also: http://www.gpspassion.com/forumsen/topic.asp?TOPIC_ID=10915
     
    Hannes Fikis, Feb 11, 2005
    #8
    1. Advertisements

Want to reply to this thread or ask your own question?

It takes just 2 minutes to sign up (and it's free!). Just click the sign up button to choose a username and then you can ask your own questions on the forum.
Similar Threads
  1. macho
    Replies:
    0
    Views:
    325
    macho
    Dec 17, 2003
  2. macho

    Audi and Volvo "Standard" Sat Navigation Systems

    macho, Dec 17, 2003, in forum: Global Navigation Satellite Systems
    Replies:
    7
    Views:
    414
    Seagull
    Jan 12, 2004
  3. Carsten Kurz

    NMEA standard document

    Carsten Kurz, Jul 13, 2004, in forum: Global Navigation Satellite Systems
    Replies:
    2
    Views:
    229
    Jack Yeazel
    Jul 13, 2004
  4. Jon Loldrup

    the NMEA-0183 standard

    Jon Loldrup, Apr 12, 2006, in forum: Global Navigation Satellite Systems
    Replies:
    5
    Views:
    727
    Mike Coon
    Apr 14, 2006
  5. PGGGA fix number

    , Jun 17, 2008, in forum: Global Navigation Satellite Systems
    Replies:
    0
    Views:
    278
Loading...

Share This Page