garmin and strava elevation discrepencies
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  1. #1
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    garmin and strava elevation discrepencies

    i just finished a ride and recorded it with my android phone using the strava app AND using a garmin edge 605. i uploaded the data from the garmin to both strava and garmin connect. the following were the results:

    -android strava app elevation calculation- 2,600 feet
    -garmin upload to strava elevation- 1914 feet
    -garmin upload to garmin connect- 1268 feet

    obviously these are some pretty huge discrepencies! all other data was the same across the board. this was the first time i used a garmin. here are my questions:
    1. is this normal?
    2. which is the correct calculation?
    3. is it possible i am doing something incorrect?

    thanks for the help!

  2. #2
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    It is ridiculously complicated to get accurate elevation data via satellite. I was in Madrid last summer at a wedding and met a PhD student at Padua in Italy who works for Garmin on this subject, and I actually asked him about it. Evidently, Atmosphere, topography, etc all effect the data. I don't think you can expect precise readings at this point. This is just my anectdotal opinion, and maybe this has improved.

  3. #3
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    Some sites have an elevation correction available.
    I know Training Peaks does.
    Check the ones you use.

  4. #4
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    I just go by what the Garmin says at the end of the ride. Every program once I upload the data seems to inflate the elevation gain.

  5. #5
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    Thanks for the responses. I'm not looking for something dead accurate. I just want to know which number is closest to accurate. My issue is that the garmin said 2 different things.

  6. #6
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    The 605 does not have a barometric altimeter so the web sites use GPS data. Garmin Connect has an elevation correction button. I would use that.

  7. #7
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    Elevation via GPS alone is not too accurate, that is why your phone/Strava overshoots. With Garmin Connect there is an option to cross-reference known elevation data using known elevation points.

    Even the units with barometric elevation like the Edge 500 and 800 will have some wonky data due to weather. I live very near sea level and start my rides at a known elevation of 15 meters. When the weather is changing it is not uncommon for me to see my minimum elevation reported as -30 m (~ -100 feet) when I upload the ride to Garmin Connect, using an Edge 500. I assume this is due to pressure change, and the anomalous low elevation is from a high pressure system moving in.

  8. #8
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    Strava recalculates at some point after you record your ride, it checks it against known elevation data.

    Saturday afternoon I recorded a ride, Strava said I climbed a little over 3,000 ft. A couple hrs later, it changed my ride to 2200ft. I was a little disappointed, so I looked into it a little deeper.

    If you look at the faq and knowledgebase on the strava site you can find the explanations.

  9. #9
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    There are three ways (relevant, anyway) to get elevation data:

    1) barometric pressure. Quite accurate if you have it, and calibrate it. Most folks turn on their computer and ride, which doesn't help that.

    2) GPS. Crapton awful for elevation, for a variety of reasons, but essentially, a low-power receiver can't pick up a good enough constellation of satellites for the trigonometry to work out very well - especially from ground level.

    3) read the GPS location data, then using topographic data, extrapolate and figure it out. Can either be decent or awful - for example, if you ride across a canyon bridge, this will assume you got your tires wet at the bottom - hella climb, though, buddy!

    Strava uses 3. A higher-model Garmin uses 1, if you are patient enough to let it. Some websites (GC, mapmyride) will combine 1 and 3 and do some fuzzy math to try to get it as right as they can figger. Some toys use 2 to display random numbers while riding.

    In other words, it's like the old saying. "A man with one watch knows what time it is, a man with two is never sure." Consider them all for crap - just pick one that suits you and go with it.

    As long as it isn't Strava.
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  10. #10
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    I posed a similar question a while back. On a ride in the local mountains, I stopped by an elevation marker and compared it against my Edge 705. The elevation difference was near 1000 ft. Most who replied said the barometer will adjust based on conditions so on any given day the Edge will fluctuate. The consensus seems to be that it was normal and that the barometer-based elevation readings from the Edge was fairly accurate (within tolerance). A good point mentioned was that if you stayed with a single site or application to analyze your rides the readings might be off but it'll always have the built-in derivation.

  11. #11
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    I use the iPhone Strava app. and in my limited testing, it usually shows less elevation than Garmins do. Initially when I upload a ride, the elevation is significantly higher, then the system recalculates and updates it (using their own map data, I'm guessing). It's the same with the Android app.
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  12. #12
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    I was up at the GRR and Mt Baldy junction this weekend. The 705 was only off by about 200 feet from the posted sign.

  13. #13
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    Quote Originally Posted by octobahn View Post
    I was up at the GRR and Mt Baldy junction this weekend. The 705 was only off by about 200 feet from the posted sign.
    Worth noting, we don't use 705's to land planes. Absolute height isn't all that important, relative height is. What's useful is to note the difference between starting and ending altitude, assuming a round trip.

    And both are aided if we don't do the typical thing of turning it on and riding as soon as the map shows up. (No, I never calibrate altitude or wait for the system to do it, either.)
    A good habit is as hard to break as a bad one..

  14. #14
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    From Garmin

    Looking through some Garmin information on the issue, I found this response from Garmin, regarding whether the 705/800 data or the data as corrected by connecting with Garmin Connect and using the available topo data (everyone uses pretty much the same topo data):

    “Which is more accurate? That is a good question. Regardless of the device or method used it is important to realize these devices are consumer grade and can introduce a level of error that is not acceptable for survey level data. The Edge 800 is more likely to have more accurate elevation information than the Edge 705 so elevation corrections should be minor. Are the "elevation corrections" more accurate than the Edge 800? Using the auto-calibration feature on the device, the accuracy is +/- 50-125ft (same as GPS elevation). With WAAS and good reception you can obtain an accuracy of +/- 25-50ft. When manually calibrating to a known elevation it is approximately +/- 10ft for the first 15 minutes. Accuracy can change due to natural pressure changes (changes in weather). Potentially the information on our website may be more accurate as many things can effect the altimeter of your GPS. There is a limit however to this potential accuracy, as indicated on our website, "Elevation Corrections has known limitations for certain geographic features such as bridges and cross country borders where different elevation datasets prevail." So in summary, in certain circumstances the Edge 800 will be more accurate than Elevation Corrections (and usually more accurate than the Edge 705), but overall the Elevation Corrections may provide the additional accuracy you need. Regardless of your choice, please be aware these devices are consumer grade and only survey grade devices should be used if sub-meter accuracy is desired."
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  15. #15
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    So how does one get bullet proof elevation readings? Possible?

  16. #16
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    Get a barometric altimeter and calibrate it frequently. Know that elevations are listed assuming a certian temperature at that elevation. and if you measure say 1000 and it's 80 degrees out, you are going to have to have a calculator to adjust to the true reading for the difference in mean temperature, because they don't figure 1000 ft elevation at 80 degrees and your reading will probably be too high. Warm air is not a dense at cold air and will affect the readings. Remember that "sea level" doesn't really exist, it's basically a virtual figure and elevation is calibrated assuming a certian temperature.
    I live pretty much at sealevel and I think that technically, if I want my altimeter to read correctly, it better be close to 60 degrees out when I check it.
    You might be thinking that it's really complicated to get accurate elevation figures. You are correct. If you look at USGS maps they have a lot of measured elevation marker locations. You can note these on your route and re adjust your altimeter when you get there to read correctly. That's about the best you can do. On top of that, most electronic altimeters (I don't think) let you calibrate on the fly. I have a Garmin Rino 130 model that does but it's too heavy for me to bother taking it on a bike ride, it's really more at home for hiking. I'm happy with my iPhone for the time being. All the GPS elevation figures I have seen that don't include a barometric altimeter are off a fair amount.
    Quote Originally Posted by respro View Post
    So how does one get bullet proof elevation readings? Possible?

  17. #17
    LC
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    On my Edge 500 I just set a elevation reference point on my front door step so that it auto calibrates every time I go for a ride. All you have to know the approximate elevation of your door step and then just turn it on and leave your bike on your door step for a min while you get your shoes, gloves and helmet on and it should recognize that point and auto calibrate.

    You can figure out your elevation is by riding to a known elevation point such as a lake or other USGS point and note what elevation it says then ride back to your door step and do a little math to figure out what it really should be and then manually put that reference point in.

  18. #18
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    Excuse my ignorance but I've not heard of strava, what is it?

  19. #19
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    Went on my first ride on my new bike yesterday down a local MUP and back. According to Strava (android app) the trail sprouted a 200 ft hill with a 17% grade while I was on my way back haha.

    I'm not going to trust Strava with elevation data at all.

  20. #20
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    Quote Originally Posted by respro View Post
    So how does one get bullet proof elevation readings? Possible?
    On what hardware?

    And for what purpose? For most of what we're doing on a bicycle, it doesn't matter what the absolute elevation is; we really care about the change in elevation. Anything with a barometric altimeter that's allowed to acclimitize before setting off will do that well. If you calibrate to the start point, even the absolute will be fairly good.

    If you want to use consumer-level GPS - and especially a phone-based GPS - and expect to get accurate elevation readings, forget about it. Some of the handheld (not cycling specific) units have positional averaging, which can gather a fairly accurate vertical fix if held in a static position for a few minutes. But that's not what we're really looking for, is it?

    Correction via topographic data has it's own problems, chief among them the scale of change. The mapping data simply isn't dense enough to gather every rolling foot of change. That's OK, really, since it's pretty silly to count little rollers as 'ascents.'

    Maybe the real solution is to stop thinking that the two rightmost digits of elevation gain mean anything, no matter how accurate they really are. If we think of elevation gain in hundreds of feet, the rest works itself out.
    A good habit is as hard to break as a bad one..

  21. #21
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    I've got the Cyclemeter app on my iPhone and it appears pretty accurate for distances but ridiculously inconsistent for elevation gains. I have no idea how its software compares to Strava or Garmin, but it makes me suspicious of all GPS elevation readings. On my bike commute route, which is pretty much the same every day, I will get elevation gains ranging from 800' to 2,000' one-way.

  22. #22
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    Quote Originally Posted by 1spaceboo View Post
    Excuse my ignorance but I've not heard of strava, what is it?
    It's a site you get free beer if you get the fastest time on a segment (climb or something like that)
    It's a fire road.............
    I'm on a road bike..........

    They have enough in common to blast down it.

  23. #23
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    I read on the Garmin forums that setting a way point on your GPS with it's correct elevation is the best way to get accurate data.

    Here's the problem I have found and tested.
    If you have some fast rollers that are not too big. You don't get any elevation gain on the way back up the other side. This is a SMALL roller, like 40 ft down, then up.

    When you upload to Garmin or Strava and use correction you appear to get those footies back.

    IMHO, just be consistent with whatever you use. Always use the Garmin data or always use correction.
    It's a fire road.............
    I'm on a road bike..........

    They have enough in common to blast down it.

  24. #24
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    Last week my buddy and I went for a ride: we both have iPhones with Strava and on all other occasions our data seem to match up. On this ride the distances we recorded were identical, but I climbed twice the altitude that he did. My maximum speed was also recorded as being 91mph while his was 34mph, but that of course was correct :-)

    Given that we were never more than a few yards apart, so using the same satellites I presume, and have exactly the same equipment, it does rather prove how inaccurate Strava is.
    Riding a TW 'bents recumbent trike, a Claud Butler MTB, a Decathlon Fitness 3 flat-barred road bike, a Dahon Jetstream P9, a unique handbuilt Moulton-based tandem, and a Scott CR1 Comp road bike.

  25. #25
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    Quote Originally Posted by 1spaceboo View Post
    Excuse my ignorance but I've not heard of strava, what is it?
    It's a system that allows you to track your miles, elevation and other useful ride data using a GPS device. Visit strava.com for more info.
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