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Thread: Height Gain: Garmin vs Memory

  1. #1
    Senior Member Fat Bloke's Avatar
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    Height Gain: Garmin vs Memory

    I'm sure there's been a thread on here before, but, having just got mesself a Garmin 305 I'm wondering why there's a [huge] difference between ascent on a Memory Map route and the height [apparently] gained as shown on the 305.

    The 305 always shows more than MM.

    Anyone any ideas?

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  2. #2
    Master Bob's Avatar
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    Re: Height Gain: Garmin vs Mem

    Describe "huge". I'd expect there to be a difference to to the way both systems work.

    MM will probably (I say probably because I don't actually know) use a limited number of actual points and then some form of interpolation to guess the bits in between. The accuracy will depend on the distance between the known points and how the interpolation algorithm fits that particular piece of land. This is a bit like getting the general shape of a slope from the contours but the details at a smaller scale could be quite different.

    Consumer GPS systems have quite a potential error, though they tend to be better than the figures suggest. First hit on Google gives - http://gpsinformation.net/main/altitude.htm

    Head down to your local track. Log one lap and see what the SW says.

  3. #3
    Senior Member ChrisU's Avatar
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    Re: Height Gain: Garmin vs Mem

    How do you get the height gain from your Garmin?
    If you are using SportTracks, then there is an option under Settings > Analysis to alter the level of smoothing applied to the elevation data, and this makes quite a difference to the height gain figure.

    By applying a greater level of smoothing you will find that the total height gain figure decreases a fair bit.

  4. #4
    Senior Member Fat Bloke's Avatar
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    Re: Height Gain: Garmin vs Mem

    Describe "huge".
    Well on a jog-ette of around 1000ft, Garmin was over 2000ft (so big a differential that I'm going to redo it to check, so please don't anyone start to question it; I am doing already!)

    BUT I have also had a chat to a fellow geek tonight who mentioned the Sporttracks smoothing issue and we had a discussion about a 'flat' run (which might show on MM as having no height gain) BUT which covers undulating ground that the Garmin would pick up, so I think I'm starting to understand the issue(s) a bit better.

    thanks all

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