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Garmin Elevation Correction

SteveDoeSteveDoe Posts: 26
edited January 2014 in Road general
Hi

I got a Garmin Edge 200 for Christmas, and am finally getting out and using it. Uploaded a 20 mile ride from Saturday, and it said the total elevation was 752 ft. When I click on 'Disable Elevation Corrections' it goes up to 1004 ft - almost 33% more. I clicked on the '?' logo but didn't understand the explanation. Looked online and the only thing I can see that would affect it is if you go over a bridge or similar, there may be a difference between the bridge level and ground level. Having not gone over one though a) how can there be such a difference, b) what is the difference and c) which one is correct - corrections enabled or disabled?

Thanks
steve

Posts

  • SecteurSecteur Posts: 1,971
    The unit has a built in barometer, and uses barometric pressure changes to calculate altitude changes. This can be affected by large / rapid changes in weather.

    The elevation correction function uses OS Map elevation data.

    Garmin says the former is the more accurate, but I find that hard to believe, so I always use the elevation correction function.
  • diydiy Posts: 6,680
    I find it can rob you of a fair amount of climb on a big ride. As much as a 10%.
  • rolf_frolf_f Posts: 15,959
    Secteur wrote:
    The elevation correction function uses OS Map elevation data.

    Are you asaying it just uses that? If it just abandons the barometric data for digital elevation map data then it negates the barometer except for en route info (which might not be what you are implying!!).

    I would assume that it corrects the barometric data against the elevation map info - so drift and absolute inaccuracy is accounted for by the digital elevation map and the detailed variation is accounted for by the barometer.
    Faster than a tent.......
  • I've not had my 800 long so I'm just getting used to all the functions, but I've seen a big difference in elevation gain (roughly 10%) compared to my smartphone that I use for strava.
  • Escher303Escher303 Posts: 342
    Secteur wrote:
    The unit has a built in barometer, and uses barometric pressure changes to calculate altitude changes. This can be affected by large / rapid changes in weather.

    The elevation correction function uses OS Map elevation data.

    Garmin says the former is the more accurate, but I find that hard to believe, so I always use the elevation correction function.

    The 200 does not have a barometer unlike the 500 and 800, it uses GPS to calculate the elevation. This is notoriously inaccurate and is normally way out from the actual total ascent you will have done, the elevation correction will likely be nearer. The 500 and 800 hundred models are more accurate.
  • SecteurSecteur Posts: 1,971
    Apologies - I have the 800, and I assumed all the other units had barometers.

    I find that on changeable days, the elevation correction is more accurate.

    On calm days, the barometer roughly equals the elevation correction figure.
  • diamonddogdiamonddog Posts: 3,368
    Escher303 wrote:
    The 200 does not have a barometer unlike the 500 and 800, it uses GPS to calculate the elevation. This is notoriously inaccurate and is normally way out from the actual total ascent you will have done, the elevation correction will likely be nearer. The 500 and 800 hundred models are more accurate.

    ^^This +1 :)
  • Cheers for the replies - I'll keep corrections enabled then- Buggar, just lost 252 ft of climbing. Must say, it felt more like 1,000 than 750 though!
  • chris_basschris_bass Posts: 4,913
    SteveDoe wrote:
    Cheers for the replies - I'll keep corrections enabled then- Buggar, just lost 252 ft of climbing. Must say, it felt more like 1,000 than 750 though!

    in that case keep it switched off :-)

    who needs to know!
    www.conjunctivitis.com - a site for sore eyes
  • True! Will just have to ride on pan flat roads, then it won't be an issue!
  • sbbefcsbbefc Posts: 188
    Whenever I go on a group ride my edge 200 always comes out with the least elevation gain vs mobile phones and edge 500s. I experemented with my own samsung phone and that also gave me more elevation. Whenever I go up short sharp ramps my unit almost never logs any elevation difference. Its a tad annoying but it gives an estimate, it will never be 100%.
  • My 200 always gives me less credit for altitude gain than the 500 my pal uses on the same route.I know I shouldn't let it get to me, but it does. :(
  • chris_basschris_bass Posts: 4,913
    SteveDoe wrote:
    True! Will just have to ride on pan flat roads, then it won't be an issue!

    you'd think but i get about 40 meters of climbing when i'm on my turbo with gps turned off!!
    www.conjunctivitis.com - a site for sore eyes
  • They're a lot of fun these gadgets. I did 75mph pushing my bike along the high street pavement the other day.

    Mind you, I'm a world class bike pusher.
  • I think the Elevation Correction feature cannot reflect accurately the most important point of the data: total elevation gain.

    Of course, without the Elevation Correction, the altitude reading may not reflect real world altitude. But we want to know how much we climb during workout. And the barometer readout is more accurate than the Elevation Correction.
    2015 Trek Domane 4.5 Disc
    http://chup.info/c/tag/trek/
  • bikingjohn wrote:
    I think the Elevation Correction feature cannot reflect accurately the most important point of the data: total elevation gain.

    Of course, without the Elevation Correction, the altitude reading may not reflect real world altitude. But we want to know how much we climb during workout. And the barometer readout is more accurate than the Elevation Correction.

    I disagree with that. The barometric reading could be wildly out if the weather conditions aren't perfect which we very rarely have in the UK. Surely the OS elevation would be much more accurate?
  • diy wrote:
    I find it can rob you of a fair amount of climb on a big ride. As much as a 10%.

    It doesn't 'rob' you of anything. If the barometric readings are incorrect then it's telling you you've done more climbing than you have actually done!
  • bikingjohn wrote:
    I think the Elevation Correction feature cannot reflect accurately the most important point of the data: total elevation gain.

    Of course, without the Elevation Correction, the altitude reading may not reflect real world altitude. But we want to know how much we climb during workout. And the barometer readout is more accurate than the Elevation Correction.

    I disagree with that. The barometric reading could be wildly out if the weather conditions aren't perfect which we very rarely have in the UK. Surely the OS elevation would be much more accurate?
    I have yet to see any great variation due to extreme temperature / pressure changes... Do you have any sample ride data with extreme weather changes, which could significantly affect the total elevation gain?
    2015 Trek Domane 4.5 Disc
    http://chup.info/c/tag/trek/
  • SecteurSecteur Posts: 1,971
    bikingjohn wrote:
    I have yet to see any great variation due to extreme temperature / pressure changes... Do you have any sample ride data with extreme weather changes, which could significantly affect the total elevation gain?

    I do - from Saturday - went out and it was clear, crisp and dry. An hour later I was cycling in the worst conditions I have ever ridden in - apocalyptic almost.

    The garmin, using barometric readings, gave only half the elevation that it usually does.

    My usual barometric readings on calmer days is usually within 5-10% of the elevation correction reading, but on Saturday it was 50%.

    I have no other explanation than the severe change in weather, but I am no expert on these things.
  • Mikey23Mikey23 Posts: 5,028
    My 500 always shows less elevation than people I ride with on the same course using 500 and 800. Sometimes by hundreds of feet. Not fair.

    I think there's a little hole underneath that it uses to register changes in barometric pressure. Is it possible that this hole could get clogged up by crud or rain... Or am I being too simplistic. I have set an altitude point outside my house that it locks onto when I go out
  • If your device is not barometric, garmin connect will automatically enable corrections, if it is like the 500 & 800 then it will be automatically switched off as these devices are more accurate and do not need correcting.
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