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  1. #1
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    Training Centre, SportTracks and Motionbased altitude discrepancies

    Hi guys,

    I've noticed that when I upload a ride from my 705 to Training Centre, I get a reasonable set of altitude/grade/speed data. When I transfer the data to SportTracks I get a much lower values for total climb and descent. When I use the same file for upload to motionbased, I get much higher values for the climb and descent stats. Also, SportTracks shows a much lower average and top speed, as well as showing my total time as my riding time.

    Anybody else have a similar problem? I believe the training centre values are the correct ones, but the differences are starting to annoy me.

    Cheers

  2. #2
    Scott in Tucson
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    There are quite a few ways to compute elevation gain, and it varies between software, as you've found. I've looked a bit at this issue with my own software:

    http://topofusion.com/climb.php

    Without knowing the internals of what MB, TC and ST are doing, it's hard to say. My guess is that ST is more accurate since TC and MB are known to be inflated. I think ST must be doing some type of filtering.

    The short of it is that if you just add up the actual gains shown in the TCX/GPX file, it's too high. This is probably what either MB or TC is doing.

    I don't know how to account for ST showing the same ride time as total time (and the avg speed issue). That doesn't sound right.
    Author of TopoFusion GPS Software. MTB+backpacking = bikepacking.net. Ride Diary.

  3. #3
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    Thanks for the help. I've had a look at your software but didn't see any maps for australia. Guess I'll stick with altitudes from ST and speeds from TC.

  4. #4
    Scott in Tucson
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    Quote Originally Posted by irongustavius
    Thanks for the help. I've had a look at your software but didn't see any maps for australia. Guess I'll stick with altitudes from ST and speeds from TC.
    TF has topo maps and landsat imagery for Australia. The tileset is called CAN/AUS Topo (combo Canadian and Australian Topos).

    Author of TopoFusion GPS Software. MTB+backpacking = bikepacking.net. Ride Diary.

  5. #5
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    Ah, my mistake.

    Still, does anybody else have similar issues with ST? The speed thing is pretty annoying. Does it have anything to do with the way I export the files from TC? I export the history as a .tcx, btw.

  6. #6
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    SportsTrack uses "Data Smoothing" for a lot of its values which means it averages it over a period of time. If you held that max speed for the length of the data sample, it would show correctly in ST. But since its taking a "X" second sample... and you only hit that peak for a second... the result will always be lower.

    Set it lower and you'll get more exact results... However, you'll probably also see spikes.

  7. #7
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    Actually all the programs have some options as to how to calculate elevation change. They can average, use topo data, use GPS data, etc... They also use different default settings.

    I don't consider it too accurate. GPS elevation is notoriously inaccurate, location data can have you over here or there where it's fifty feet higher and the barometer sensors are "good enough" but not exactly on the money either.

  8. #8
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    Some SportTracks basics

    Hi folks.. SportTracks have its own definition of whats uphill and whats downhill

    If you go into the Select View link down left when you are on the Daily Activity page, then select Categories, and finally climb zones. You'll see that there's a 2% cutoff ascent/descent - and this is what makes up for the difference between Garmin and ST.

    See what difference it makes on a 85km ride I have on file (ascent/descent):

    Garmin : 839/842m
    ST 2% : 552/570m
    ST 1% : 734/734m
    ST 0,5% : 786/793m
    ST 0,1% : 805/809m

    The Edge 705 has a barometric altimeter, so I think that is fairly accurate. When I first started to look into these differences, I thought that any climb from a given lowest altitude would be considered climbing, and that any descent from a given peak would be considered descent. From the ST climb zones, you'll see that this is not the case.

    My guess is that the climb figures accuracy on Garmin is the closest to my original thoughts.

    A tip I picked up from another website:
    * Categories view -> Climb Zones
    Barometric Edge owners use +/- 0.1%. The default is +/- 2%, better for the non-barometric devices.

    Rgds,
    DD
    Last edited by DuetDeux; 04-06-2009 at 04:40 AM.

  9. #9
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    this has been discussed before, motion based adds 10-20% to the vertical climb data. changing the gravity options does not help.

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