Why such different elevation corrections? (same route logg 1790m, 2615m, 3468m elev gain)

I rode with a friend the other day . I use a Garmin FR 305, he uses an IPhone. 

When I uploaded FR305 -> Strava, the elevation gain is 2,615m, see  http://www.strava.com/activities/138096662

When I uploaded FR305 -> Garmin Connect, the elevation gain is 1.790m (with elevation correction enabled)  and 1.724 m (with elevation correction disabled)  see http://connect.garmin.com/activity/494258370

My friend uploaded from IPhone Strava app , he logged 3,468m, see  http://www.strava.com/activities/138064391 (maybe this activity is not visible to public) 

The Garmin FR 305 is pretty accurate, I have compared data from Garmin Edge devices, and the difference < 5%

It would be good if it was possible to disable the elevation correction in Strava, it is not working very well. Garmin Connect. has the possibility to disable elevation correction even though it does a good job.  Maybe the elevation correction algorithm / database works fine in the US but where I am, it is no good.

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Comments

86 comments
  • Official comment

    We've announced some changes to our method of calculating elevation data for Strava Activities. At the end of the article is a feedback form you can fill out to ask questions and report issues. Thanks and let us know what you think. 

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  • Hi Jens,

    Thanks for passing along the good examples - it is interested to see how other sites handle elevation gain statistics. 

    We use the same database as Garmin for our corrections, so it's unclear why the two differ so drastically. I'm going to pass these examples on to our developers for further research! 

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  • Hi, I be the same problem. I m using a Samsung S4 whit barometric sensor. The elevation registered during the ride is correct... But when I upload the track it add about 30% elevation. Is it possible to disable correction algorithm?

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  • I would like to second this same issue thou I am using a Garmin 500 and also recording on Strava iPhone app and have noticed the significant disrepancies.  

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  • same issue here with Garmin 500 compared with regular major differences with my cycling group

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  • Hi all

    I have a cycling GPS Bryton 40T  with barometric sensor. The  elevation of all the files I uploaded on Strava (.tcx or .gpx is the same) were corrected in a wrong way (about 30% more). The same file uploaded on the Bryton site give the correct indication

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  • I have the same problem with elevation. I use android application and when the ride is first uploaded it's very accurate in terms of elevation, but then Strava's elevation correction kicks and messes up the whole thing!! On the last ride at first it said ~540m of elevation which was very accurate but still a bit too much. After the "correction" it jumped to ~740 and it's totally inaccurate. And this is just on a short 44km ride, when there are longer rides it's so much worse. The GPS data from the phone is fine, the elevation correction is absolutely worthless and misleading. Please fix it already or at least add an option to revert the elevation correction.

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  • I have the same issue. 

    Gained altitule of my workout below was about 3000m, but it was incorrectly corrected.

    The elevation is 6800m, twice as the record!

    It seems to sum up tiny elevational noises.

     

    http://app.strava.com/activities/156559897

     

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  • Hi Makoto - Thanks for the information. I've sent your file over to the engineering team, and will work on getting this added to our list of devices with "trusted" elevation data. After that happens, Strava will be able to read the elevation data collected by your device. 

    Gio - regarding your Bryton device, I believe we're working to do the same thing if we haven't done so already. 

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  • I have the same issue. I am getting about a 500 meter difference between iPhone uploads and Garmin 500 uploads, both devices were used at the same time. The delta is larger after the automatic Strava 'elevation' correction is applied. The iPhone gives consistently higher total elevation gains than the Garmin 500.

     

    Thanks

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  • Perhaps some of you would be interested in adding your votes and comments to this feature suggestion:

    https://strava.zendesk.com/entries/35578550-Revert-to-GPS-based-altitude-when-corrected-elevation-is-erroneous

    Also, there is an interesting discussion on this topic happening near the end of this forum: https://strava.zendesk.com/entries/25860845-Option-to-undo-Elevation-Correction-and-revert-to-Barometric-Altimeter-

    @Gary - your observations are to be expected, within reason. The dataset collected by your Garmin's Barometric Altimeter will be fundamentally different than map-based elevation that is corrected by an elevation database. 

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  • I do not really expect a 1500 ft difference (5800 ft vs 7300 ft) between the two devices. The numbers were somewhat closer between the iPhone and the Garmin before the auto correction was applied. If the algorithm is based on measured, on the ground topology, when I apply the correction to the Garmin data shouldn't it be the same as the corrected Iphone data over the same route? After applying the elevation correction to my Garmin data, there was only a 0.5% difference when compared to the raw Garmin data, but still a 500 meter difference to the iPhone data. Hope this makes sense. Thanks, Gary
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  • Thanks Gary - I'll try to offer up an explanation, and I hope it helps. 

    A barometric altimeter best measures relative elevation changes based on atmospheric pressure. Since changes in atmosphere pressure are very small, and changes are gradual, the resulting dataset will be well "smoothed". Also, the changes in elevation relative to each other will be accurate, but the absolute readings from your Garmin, for example, may not read the exact elevation at that location. 

    An elevation database created by surveying the land surface will essentially divide the whole world into a grid of squares, with each square reading one value for the average elevation measured in that area. When we use this database to calculate your elevation, we see which "square" each of your GPS coordinates falls into, and use that as the elevation value. A few problems - for much of the world, the dataset is divided into squares measuring 30 meters on each side. For locations with complex topography, a lot can change from one square to another, and the average value of one square might only paint a limited picture of the elevation changes in that square. Pair that with GPS accuracy, and you may have a decent amount of recorded GPS coordinates that place you in a "square" that you were not actually in. Thirdly, this resulting elevation dataset for your activity may not be very smooth, and may have large changes in elevation from one point to another. This can cause issues with inflated elevation readings. 

    Also keep in mind that when you recording with two devices, you're generating two different GPS files, and each GPS will record different coordinates even if they traveled the same route. GPS is a bit of a whacky technology, and has an average of + or - 50 feet accuracy pretty much at all times. So, if you take two different recordings, and correct them both using the elevation database, you will get two different values (also recording intervals play in here, and a Garmin has a variable recording interval while the mobile app is recording every 1-2 seconds). 

    What I'm attempting to accomplish here is to paint a more detailed picture of the factors behind the scenes with your elevation correction, and try to explain some of the subtleties of elevation data, and why there can be some variation based on each GPS recording, device, and method of data collection used. 

    Let me know if that explanation helps! 

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  • Doh! When I rechecked the numbers the corrected iPhone data was the same as the corrected Garmin data. Now I just have to figure out which is more accurate. The barometer or the mapping data.
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  • Why does the strava route builder not deduce the same route elevation as the corrected version. Rapha rising challenge requires977m of vertical gain per day. I used the route planner and came up with a route that has 865m of elevation gain. I rode the route and my phone (Samsung s4) reported 878m, then the ride was corrected by strava to 765m. If strava is using topographical database to correct ride data (reasonable considering GPS elevation inaccuracy) why does the route builder not come up with the same total?

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  • HA!!! Your lucky James. My elevation showed at 800 metres. That was after loading. I looked again 5 minutes later and it had been smoothed to 97 metres elevation gained.

    I loaded the same file to my Garmin account and it showed 637 metres gained.

    Now I know the segment I road and according to the Strava site the elevation gain on that segment is 27 metres and I was riding repeats from a little lower on the slope. BUT even if I was to accept that it was only 27 metres since I did 27 climbs that should still be a minimum of 675 metres.

    Looks like I'm pulling out of the Rapha Three ranges challenge.  At this rate I'd have to climb at least 53,000 vertical metres according to the Strava site to qualify. 

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  • Hi Elle, thanks for the explanations. These make sense and I now understand the differences in different GPS devices' altitudes - thank you. However, I would always expect corrected GPS figures to match  the altitude figures in the Strava Route builder as surely Strava uses the same corrected data for these functions? This is the Strava app so we should all be using the same corrected figures and playing off a level field - Pun intended ;-) I am new to cycling, loving it and the challenges in Strava. I am using your route builder for a climbing challenge which is tough enough but so far all of my rides are getting "corrected"/reduced - sometimes by 25%. This is in comparison to your own route builder. Help!? 

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  • I'm having similar elevation profile - related problems, that are driving me crazy. I'm recording with SGS3, which has barometric altimeter. Resulted GPX files represent the elevation profile pretty accurately, but then Strava corrects it with it's 30x30m elevation database and screws it baaadly. Often I get "downhills" (sometimes even longer than 100m) on the tracks, that were actually pretty steep uphills only.

    If I may suggest, PLEASE make an option to either show elevation profile from track or database corrected one. Maybe it would be even better if You could always show both (in different color) and also show elevation gained for both.

    I put a lot of effort in creating quality segments, but most of the time they have elevation profile not even close to reality because of this "corrections" ;(((

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  • Hi Elle,

    I experience problems with inflated elevations calculated by STRAVA, here is an extreme one with an error >100%: http://www.strava.com/activities/266235362
    This hilly ride was logged with MotionXGPS on an Iphone.

    MotionXGPS calculates 
    Ascent 2.060m, Descent 2.049m which seems to be accurate.

    When I simply add all ascents and descents in the GPX file, Excel calculates
    Ascent 2.641m, Descent 2.634m, which seems ok also since its without smoothing.

    Strava however shows an elevation gain of 4.340m! 

     

    There seems to be a systematic mistake somewhere in STRAVA's server's algorithm. also this one http://www.strava.com/activities/266575582 is inflated. STRAVA=4.064m, MotionX = 2.940m.

    Interestingly the graph seems to be accurate, when you estimate the gains from the graph you end up around 2.900m.

    Cheers

    Charly

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  • I've Samsung Galaxy S3, which has barometric sensor. When I record my rides with my phone using Strava Android application, I'd love if the app would also record barometric data from the phone, and use that for elevation instead of Strava's elevation database.

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  • Seems that in mountainous areas Strava is taking data from contours and when you're riding along the edge of a cliff, a 10m error on position means that it thinks you've gone up the cliff. See this segment https://www.strava.com/activities/267853448/segments/6272417938 which I rode twice last week and has plenty of riders doing it so should be more accurate: this segment is a constant descent, no midway climbs as the profile suggests. Also this one, on the same ride, https://www.strava.com/activities/267853448/segments/6272418010, doesn't suddenly jump to 250m , it goes through a tunnel!

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  • I just completed a cross race. Eveyone who had a Garmin has the correct(ish) altitude. From my Magellan Strava recorded a zero altitude. Go to Magellan and I find I should have had 70 meters. Erase the old one, down load the GPX and it is still zero. Don't understand. Cross race is short and tight so why do the others get recordings in Strava for altitude and I don't? Is it something with using a Magellan?

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  • Strava people, can you please consider to add the possibility to disable elevation correction? The raw elevation data from my FR310XT is fine, the corrected values are totally wrong.

    Since it has been nearly a year now and nothing has happened.. I'm thinking of  modifying the device type in the data file to fake an barometric device (edge e.g.)

    maybe stop using Garmin Express and revert to copy data from Garmin via API (copymysports) 

    Ideas anyone?

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  • Rode side by side with friend today both using garmins mine 200 friends 500. However when we uploaded my friends elevation was 500 ft more? 

    What's happened?

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  • @James, 

    The Garmin 500 and 200 record elevation data differently. The 500 has a barometric altimeter and the 200 does not. We automatically correct the data using an elevation database for Garmin 200 uploads, and we preserve the raw elevation data from the Garmin 500.

    Hope that helps answer your question!

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  • @ Elle Anderson

    Elle - I've read the reasons why elevation correction might be different between devices.  My question thought, why is there a difference between the elevation correction algorithm and the Strava Routes elevation algorithm?  are they not using the same DB to calculate such information?

     

    For example, the following activity:

    https://www.strava.com/activities/295201251

    shows an elevation gain of 11,660 ft.

    If I create a route based on the above ride, it generates an elevation profile of 6,483ft (much more reasonable).

    Thoughts on this?

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  • In Australia the problem is the same Strava's elevation correction universally overestimates elevation gain by 60%. Hopeless. Only Garmin barometric altitude data is allowed
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  • @Francisco - great question.

    For Strava Routes, we're testing our own elevation database. We've aggregated "trusted" data from activities with barometric altimeters. This creates our own database for elevation based on Strava data. This database doesn't represent just one person's barometric altimeter data, but is normalized across many device files for maximum accuracy. 

    For now, this elevation data is only available for Routes that match our Routes basemap. We are not yet able to apply this same elevation data to uploaded Activities, but this could be possible in the future with more development. 

    In theory, with a Strava elevation database, elevation could be automatically corrected across devices regardless of whether they have barometric altimeters, offering better consistency for elevation on Strava. 

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  • @Elle,

    Thanks for the response.  I will hope that solution (strava's own normalized elevation data) will be pursued and implemented.

    I share the sentiment of others when I see garbage readings such as the ones listed in the sample ride I posted.  Not to mention it makes the climbing "challenges" a joke.

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  • Might be nice if the uploaded data ends up with 0-50 ft elevation to be allowed to run the correction algorithm regardless of a barometric device being detected.

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