Is the elevation recorded in a GPX file on a 60Csx only GPS based?

Discussion in 'Garmin GPS' started by Howard, Feb 24, 2016.

  1. Howard

    Howard

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    A GPX file trackpoint or waypoint includes elevation data. In a 60Csx, is this based purely on the GPS elevation, or is it also based somehow on the barometric altimeter data?

    I understand that the GPSMap60Csx can correct the barometric elevation using regular GPS elevation checks (apparently a 30-minute rolling average of barometric and GPS elevations), but would have assumed that this is a one-way street, that the recorded GPX data would be based on raw GPS elevation data instead of some correction factor.

    There doesn't seem to be any documentation about this online that I can find.
     
    Howard, Feb 24, 2016
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  2. Howard

    Nuvi-Nebie Moderator

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    I have found an article here :-
    http://www.xcmag.com/2011/07/gps-versus-barometric-altitude-the-definitive-answer/
    that states :-
    Garmin and MLR
    Garmins always reference the height above the geoid, not the ellipsoid. Some Garmins without pressure sensors, and all MLRs, have no barometric capability at all. These instruments can only display and record GPS height.

    Other Garmin GPSs with a pressure sensor are commonly used in free flight. The 76S and 76CS(X) and the 60CS(X) are popular first instruments.

    The units display geometric height on the satellites page as ‘GPS Elevation’. Barometric elevation is displayed as ‘Elevation’ on the Elevation page and is a selectable field on all other pages. It is this barometric Elevation that is recorded in the track log.

    I appreciate that the GPS's Track log and a GPX file are not the same thing, but I think it would use the same data
     
    Nuvi-Nebie, Feb 24, 2016
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  3. Howard

    Howard

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    Thank you for that - really interesting to see. There doesn't seem to be any official Garmin documentation on this; I see references online now to several requests to document how elevation is recorded, or to make the baro/gps recording optional.

    Frustrating that the GPX records an elevation value which has been subjected to a correction algorithm which is inaccessible after data are recorded!
     
    Howard, Feb 25, 2016
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  4. Howard

    Nuvi-Nebie Moderator

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    Yes, I have to say that before I found the above, I would have guessed (wrongly), that the unit would store GPS elevation, because even though it may be incorrect, it won't have been influenced by variations in barometric pressure due to the weather's highs and lows, also the user can 'fiddle' the figures, either inadvertently or purposely by manually entering the wrong barametric pressure / hight above sea level
     
    Nuvi-Nebie, Feb 25, 2016
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