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  1. #1
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    Reputation: Jski1911's Avatar
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    Elevation gain different when downloaded to Motionbase

    Does anyone know why the total evation gain on my Edge 305 would different when downloaded to Motionbase? The unit says I gained just over 6000', but the Motionbase site says that I gained just over 6800'.
    Speaking as a completely objective, third party outsider with absolutely no personal interest in the matter...

  2. #2
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    I've been using motionbased with my 305 for almost two years.
    motionbased always adds about 10-20% of vertical too all my rides, regardless of settings on either end

  3. #3
    On MTBR hiatus :(
    Reputation: Speedub.Nate's Avatar
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    It appears that MB and some other mapping software overlay your recorded GPS route over their terrain database, and recalculate elevation gain based on their contours.

    I've selected options to "use GPS elevations" in other software. When viewing this in 3D mode, the result is my tracks are above and below the terrain as depicted. Often where the trail has a consistant incline, which is reflected in my steadily climbing GPS track, the terrain depicted in the 3D view will dip and dive, due to these erroneous contour interpolations.

    The thought process may be that contour maps are more accurate than elevation calculations by GPS receivers. In my case, my Vista HCX elevation recordings are "smoothed "due to a built-in barometric altimeter; the non-baro models have "spikier" elevation plots.

    In all, I trust my non-GPS, altimeter-equipped bike computer to give me the most accurate elevation gain information for a ride. The inflated Total Gain my GPS spits out is often utter nonsense, and the numbers I see in software is even worse.
    speedub.nate
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  4. #4
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    Reputation: Jski1911's Avatar
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    Thanks for the explanation gents!
    Speaking as a completely objective, third party outsider with absolutely no personal interest in the matter...

  5. #5
    On MTBR hiatus :(
    Reputation: Speedub.Nate's Avatar
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    Here's a great example (I don't have the original GPS file handy to show it "in the air").

    The big "dimple" isn't there. That whole area is a plateau on top of the hill. In fact, the light green splotch alongside the trail is a very small lake.

    Also, note in the foreground to the left, the yellow track meanders off the trail (visible through the trees) just enough that it "falls off" into a ravine. Had my track been recorded spot on, this wouldn't have been a problem, but now that it's a few dozen feet off the trail, some incorrect elevation loss & gain is realized.
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    speedub.nate
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  6. #6
    Slowest Rider
    Reputation: BigLarry's Avatar
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    In a lot of calibrations on known elevation differences, I find all of Garmin's newer GPS units show climb indications are about 15% low. However, the Garmin altimeters are very accurate and the correct altitude is recorded.

    I find uploading barometric altimeter data from a GPS to Motion Based is the most accurate way to get total climb.

    Most of Garmin's newer GPS units are reading 15% low on total ascent, even on a climb up a uniform hill where such a lower climb reading than "top minus bottom elevation" is mathematically impossible yet still shows 15% lower. (My older Vista worked fine though.)

    The worst is to use Motion Based "gravity web", which uses your position to estimate altitude. All sorts of position errors lead to false altitude gain, often over 30% higher total climb than the real number.
    It's not slow, it's doing more MTB time.

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