Ascent calculation is inaccurateFORUMS HOME SEARCH FORUMS

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    plotaroute admin   Wednesday 12 Sep 2018 09:42:25

    Hi Jose, that's an interesting anlaysis of the psychology - I like your Trump analogy! Personally I've found that different sources often vary by more than 10%, however, regardless of that, it wouldn't be possible to replicate figures from other sources without knowing the exact formulae they use, so having a "Garmin" estimate or a "Fitbit" estimate isn't feasible I'm afraid.  Also, I think it would complicate things and cause consfusion. I'm afraid we've nailed our colours to the mast on this one - we'll be constantly chasing our tail if we try to replicate estimates from other sources, so we've decided to leave things as they are and focus on the many other Feature Requests that we've received. As per our post below, the best advice we can give is to stick with one source for estimates of ascent. 


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    jose camara Tuesday 11 Sep 2018 23:52:50

    I agree with the geometry, topology, mathematical side of it, John is correct in depending on how you define ascent, specially sampling distances, thresholds, you will have very different numbers.

    OTOH, in practical terms, many of us are used to numbers given by devices with altimeters that have an intrinsic slow average to it, but somehow RWGPS, Strava and Garmin seem to agree on their "fake numbers" (to paraphrase trump) by 10% or better.

    I prefer to generate a route and have a estimate of climb that is just as fake, so while I am riding I can know "done 2/3 of climb already, great".

    One simple solution is to have options on the program to have ascent (and descent) with options for "Garmin estimate", "Fitbit estimate", "ant walk", whatever. This way it can be as useful as other existing programs that are "perceived to be correct" (because they match the ride computer), and still give the higher, "more accurate" estimates for the purists.

    At least distances seem to be nearly identical for every app out there.


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    N/A N/A Saturday 23 Jun 2018 22:55:09

    Hi! As someone whose background is in geomatics I confirm what John says.


    The "accumulated climb / descent" figures that we use are a useful fiction that can only serve as an approximation. Technically, we are faced with the problem of trying to measure non-rectifiable paths (i.e., curves not having a finite length). The problem was fascinatingly well explained in a fairly accessible manner by Benoît Mandelbrot in his 1967 paper "How Long Is The Coast of Britain?".


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    plotaroute admin   Thursday 14 Jun 2018 14:46:17

    Hi Pierre,

    I'm afraid we don't plan to make any further changes to our elevation stats. Every system calculates these differently and there really is no definitive "correct" figure, so we'll be constantly chasing our tail if we try to match calculations from other sources. The best advice we can give is to only compare ascent calculations from with those of other routes mapped on, rather than with figures obtained elsewhere.


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    Pierre Chartier   Thursday 14 Jun 2018 08:05:10


    Any update on this ? I ride a lot in the Alps, always using plota route as it is really a great tool.

    My impression is that the difference between what plotaroute indicates and reality (measured on a map, or with several GPS or altimeters) has decreased, but remains at least 30% too high.

    I know using a GPS to compare is not very accurate (a GPS can also be wrong), but I did comparisons with "famous" climbs (for example some Tour de France stages which are well documented)  which are 100% climbs (no up and downs), with known altitudes (where several web sites or maps agree on the altitude) and every time plot a route overestimates.

    But still a great tool despite this!


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    plotaroute admin   Friday 15 Dec 2017 08:45:44

    Thanks for sharing this feedback Dave and for putting your faith in plotaroute. It’s hard for any one application to claim they have the most accurate ascent figures, as it really depends on your definition of ascent, but I think the most useful thing you can do is to always use the same system when comparing ascent figures for different routes and I'm very pleased you've chosen plotaroute for this. 


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    Dave Fellwalker Thursday 14 Dec 2017 12:12:03


    I have been experimenting with various Garmin and Satmap GPS units and .GPX files with my two Ramblers groups, many members of which have and use these. These units have always recorded very different results in their Trip Computers by the end of a walk.

    Personally I have an old and trusted Garmin Etrex 10, which records distance but ascent can only be interrogated via the .GPX file. I use Plotaroute to plan my routes for both A parties. I'd welcome advice from anyone who reckons that I'd get superior accuracy from buying a newer GPS, and which one to buy!

    If I download my plots to various mapping apps they all read remarkably similarly for distance, usually within 3%. Ascents vary widely. If I save my Etrex 10 trip computer distance it always reduces when the .GPX file is saved and smoothed. I guess smoothing has a similar effect on ascents.

    Here's an example:

    Track_13-DEC-17 015026 PM.gpx   kms Metres Scale
    Plotaroute Open Source mapping 18.294 419 Unknown
    WalkLakes 18.3 549 1:25,000 mapping
    Ride with GPS 18.3 441 OpenSource
    Where's the path 18.2 549 1:50,000 mapping
    Dave's Trip computer 18.41   1:25,000 mapping
    Garmin Basecamp 18.3 658 OpenSource
    Contours counted visually on WalkLakes   400 1:25,000 map

    rom my personal experience of a short trial OS Maps ascents recorded on my Etrex record are far higher than even Garmin Basecamp! So ..........

    I've decided after all my research to use Plotaroute for my route plots, distances, timings and ascents and find it as accurate as any other app, easier and quicker to use and more accurate than most, it shows routes on the ground that don't often exist on OS maps, and is reliably within a safe margin of error especially where I need to plot a route within a limited time window, for example when my group has a coach ramble and we need to get back to the coach by a certain time as demanded by the driver's working hours.


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    eric borghs Friday 17 Jun 2016 07:03:24

    Thanks, John, for pointing to that option. Sorry for not looking into all of the features in the first place.

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    plotaroute admin   Wednesday 15 Jun 2016 14:43:53

    Hi Eric - Thanks for your kind feedback about the site.

    Hopefully we can make some changes to the ascent calculations soon - I notice it is moving up the Feature Request list!  And also, there is a request to add a Total Descent calculation, which is something that could be done at the same time.  There is already an option for users to choose different elevation intervals though in the Route Profile tool. There would need to be a standard interval by defaut to make the figures comparable between different routes on the site.


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    eric borghs Tuesday 14 Jun 2016 12:37:21

    Hi all,

    First, I am really blown away by the fast, easy and intuitive way to create a route! Really great tool!

    But also I voted for adding the more realistic ascent calculating approach. Maybe let the user choose the interval as an advanced option?