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Garmin / Strava Elevation Differences

  • 16-07-2014 7:56pm
    #1
    Registered Users, Registered Users 2 Posts: 12,863 ✭✭✭✭


    Can anyone explain this?

    i went out with a mate yesterday. I have a Garmin 200 and he uses Strava on his Android phone.

    We both did the same spin. His is recorded directly to Strava from his phone - mine is uploaded to Strava from my Garmin.

    I climbed 399 metres - he climbed 448.

    Why the difference?

    BTW - I have elevation correction turned on with Garmin Connect. If I turn elevation correction off, I get a climb of 423m.

    EDIT: Same thing happens with average speed. I got home last week with my Garmin telling me 29.1km/h but when I uploaded to Strava I was pegged back to 28.9km/h......


Comments

  • Registered Users, Registered Users 2 Posts: 718 ✭✭✭gaffmaster


    His phone was in his pocket, so every time he got up out of the saddle to climb it registered another meter in altitude gain!


  • Registered Users, Registered Users 2 Posts: 12,863 ✭✭✭✭crosstownk


    gaffmaster wrote: »
    His phone was in his pocket, so every time he got up out of the saddle to climb it registered another meter in altitude gain!


    He's not that tall and he's not one for getting out of the saddle either!


  • Registered Users, Registered Users 2 Posts: 283 ✭✭Diggabot


    I was actually reading about this today... I've a garmin 500 and it get a -27 meter starting point. It's to do with the barometric sensor in the garmin. I was reading the resetting the device should help but you may need to manually adjust in the device.


  • Registered Users, Registered Users 2 Posts: 391 ✭✭XtotheZ


    there always off, look at races on strava where there 20 different lads uploading stuff. theres never two the same


  • Moderators, Category Moderators, Arts Moderators, Sports Moderators Posts: 50,895 CMod ✭✭✭✭magicbastarder


    i remember reading that the elevation accuracy in GPS is deliberately reduced (on the request of the american department of defence), and if i'm not hallucinating that memory, the inaccuracies could build up over an hour or two to account for the difference, possibly?


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  • Moderators, Category Moderators, Arts Moderators, Sports Moderators Posts: 50,895 CMod ✭✭✭✭magicbastarder


    General Accuracy Requirements

    GPS measurements for horizontal distances are accurate to around 10 yards, according to the manufacturers. This is largely a worst-case scenario. Most are accurate to two to three yards. Altitude is rated at about half the generalized accuracy of horizontal accuracy; most manufacturers say that altitude is accurate to within 15 to 20 yards. Because of this, many GPS receivers can take manual calibrations to give updated altitudes compared to the reference altitude set for better accuracy.
    http://techchannel.radioshack.com/gps-elevation-measurements-2264.html


  • Closed Accounts Posts: 663 ✭✭✭laraghrider


    Upload it to Garmin first and do an elevation correction and you're sorted.


  • Registered Users, Registered Users 2 Posts: 338 ✭✭Budawanny




    Also to get to that degree of elevation accuracy using GPS alone you need line of sight to 7 satellites.

    Garmins use a built in pressure based altimeter.


  • Registered Users, Registered Users 2 Posts: 1,100 ✭✭✭clog


    Set an initial known elevation point at the start, outside your house for example. Put this in memory and the barometric sensor will start at the correct elevation. If you can't do this leave the garmin on for a few minutes before you start as it takes much longer for the elevation to 'settle down' than the position.
    It could also be in diggabot's case that corrupt elevation data is causing it to start at an incorrect elevation -27m. I have had this problem before and clearing out the satellite cache on the device has solved the problem.

    I wouldn't overly worry about differences though between devices . The most accurate overall figure I would guess though is on garmin connect with the elevation corrections on as this data is matched to actual map data.


  • Registered Users, Registered Users 2 Posts: 12,863 ✭✭✭✭crosstownk


    Budawanny wrote: »
    .

    Garmins use a built in pressure based altimeter.

    Not the Edge 200 - it uses a GPS based altimeter. Maybe this is less accurate than the barometric type.


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