Ascent calculation is inaccurateFORUMS HOME SEARCH FORUMS

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    Paolo Grinzato Sunday 21 Mar 2021 08:38:02

    Hi all, In my little experience with plotaroute I've noticed e 40% error in ascent calculation.It is interesting that plotaroute is the only one (among the different apps I use) that over estimates the ascent.

    I can tell you that all other apps have the same calculation , at least within few meters, tha precesily overlap tha reading of my gps device. To give some numbers, planned route was more tha 520m ascent with plotaroute, while on the same track otehr apps expected 385m that was  exactly what I recorded.

    Moreover, if I look to the elevation only, it is accurate as all other maps.

    It is disappoint that such a good planner gives an incorrect prediction, that can't be helpfull if you are concerned about the effort reqiuired to perform that trip (ascent).

    Thanks! Any suggestion is welcome.

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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?



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    Pierre Chartier   Monday 23 May 2016 18:10:06

    Thanks. I voted or it.

    There is just near my place an ascent which is pure uphill on 18km. It's about 1400m ascent. Next time I climb it I will see what plot a route gives and compare it both with a map and with what my GPS gives.

    I will let you know.

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    plotaroute admin   Monday 23 May 2016 11:12:28

    Thanks Pierre for your feedback - glad you're enjoying using the site.  Adding some smoothing to our elevation data is on the Feature Requests list but please vote for it to move it up the list (number 52).  Please be aware though that GPS devices are not a reliable bechmark for ascent calculations - we've looked at numerous examples of raw GPS recordings and usually find big gaps in the data (probably due to poor signal reception) that result in ascent figures being understated.


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    Pierre Chartier   Saturday 21 May 2016 17:44:45


    I think this would be a nice idea, not to make it comparable with other applications but also to make it more accurate.

    I leave in a mountain area (French Alps), so I ride frequently rides with a lot of elevation. The total elevation on plotaroute is often at least 50% too high. Example : I rode yesterday

    Total ascent is 2671m on plotaroute. Yesterday a friend and I measured a total ascent of around 1820m (we had two different GPS)

    I found similar results on pure uphill rides when comparing also with the altitudes written on a map.

    The percentages as well are too high. I frequently get on plotaroute a max percentage of more than  35% (38.8% on the ride above) which is impossible to climb on a bike (at least for me!)

    Keep on the excellent work you are doing. Your site is great!


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    plotaroute admin   Wednesday 11 May 2016 12:48:16

    Glad you like the site Claudio - thanks.  

    The Total Ascent figure shown on the elevation profile as you are plotting a route is just an estimate based on a small sample of elevation readings (a maximum of 500 at equidistant intervals across the route)  - a more detailed calculation is made when you save the route using elevation readings at 30m intervals, as it isn't feasible to recalculate this in such detail as you are plotting.  We do adjust the 'as-you-plot' figure by a factor to try to compensate for the smoothing effect of using elevation readings at bigger intervals, but the impact of using bigger intervals differs according to the amount of bumps and dips on the route, so it will sometimes vary quite a bit from the final figure.


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    Claudio Crivelli Wednesday 11 May 2016 09:40:17

    Reagrding ascent calculation I have to say estimation by Plotaroute is quite good during the editing. But once I saved the track, I see even a +40% increment without any reason.

    If I go back to editing the same track and I just move the start-stop point by few meter, the system updates the total ascent and the number comes back to "real" values. So to me the problem seems to be related to the SAVE process... Even without saving, if I switch to the profile tool I see the increased value... It seems the right value is given only during the editing and only in the "HILLS" area (below the map).

    Is this happening only to me?



    ps: plotaroute is a great tool! many compliments!

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    plotaroute admin   Friday 06 May 2016 09:50:14

    I'm happy to look at smoothing the elevation data a bit to reduce the total ascent figures  if enough people feel this would be helpful.  I've added it to the Feature Requests list (number 52), so that anyone interested in this can vote for it.  At the moment only 3 people have asked for this on the posts below and we have over 50,000 registered users on the site, so I need to consider that some people may prefer that the data wasn't smoothed.  My personal opinion is that it would probably help for the Total Ascent figures to be more comparable with other applications and, so a bit of smoothing is probably a good idea, however  I think I would only want to increase the sampling interval from 30m to 90m.  This would also mean having to recalculate the Total Ascent figures for every route on the database, so it would be quite a big task.  And there would be additional development work if we also smoothed the actual elevation profiles, but if smoothed data is used to calculate the Total Ascent figutes it would probably be best to use smoothed data for the elevation profiles too. 



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    Nisse Son   Wednesday 04 May 2016 20:58:57

    "I'm afraid we don't have the resources to keep doing detailed analysis of individual routes.  If Google's data isn't giving you the accuracy that you are looking for we have little chance of bettering that!"

    I don't think anyone expects you to, but you could use what the other services do, heck you have already built it yourselves! :-) The Google data doesn't have the accuracy to be used for this application as raw data, it has to be smoothed a bit. This is what other services do to make the accumulated numbers more true to the real world. Without this, the totals can be off by 50%, as previously shown.

    But good news, there is an easy way to solve this! What I (and possibly others) ask for is just that you use smoothing for the data. Plotaroute have the feature already in the "Route Profile Tool". If I use this for any of my done rides and set "Filter Bumps" to 10.0% and "Elevation Intervall" to ~200 meters, both the hills inclination and total data matches reality. If e.g. these numbers would be default things would be as I (and possibly others) would like it to be. 

    Not only are the totals off as of today (annoying, but still just numbers), but the Route Timer-estimation gets so wrong it is useless. If the Route Timer and Download features used the smoothing from the "Route Profile Tool" instead of raw data, then those feature would be much more useful.

    So, my suggestion is: make some smoothing default (if not for all users all the time, but could we please have it on a user base?). This will solve this problem to at least the use cases I have seen in this thread.  

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    plotaroute admin   Tuesday 29 Mar 2016 10:37:27

    I'm afraid we don't have the resources to keep doing detailed analysis of individual routes.  If Google's data isn't giving you the accuracy that you are looking for we have little chance of bettering that!  plotaroute is a tiny operation and is offered as a free service.  Yes, we do have an ad-free option but the nominal annual fee for this just offsets lost advertising income - our total revenues are not enough to pay the salary of one person let alone a whole team!  The project is very much a labour of love at present that I hope will grow into something bigger, so please bear with us, as we can only achieve what is feasible and within our means.

    I understand the desire to try to get our Total Ascent figures to match those from other systems, but my main concern is to ensure that people can compare routes that we have on plotaroute on a like for like basis, so I would not want to apply different rules for different routes, for example by sometimes using GPS elevation data in place of the data we would normally use.  Also, we would need to make fundamental changes to the system to do this, as elevation data is not captured and stored on a route by route basis at present.

    I think one way forward would be to calculate two figures for the Total Ascent - a 'raw' figue (the current one) and a 'smoothed' figure (sampling elevation readings less frequently).  This will retain the integrity and comparability of the existing routes while provding an alternative figure that reflects the degree of smoothing that is probably found in other applications. I can add this to our Feature Request list if you feel this would be helpful, where anyone interested in it can vote for it.  As you'll appreciate though, there are many other users of plotaroute who are asking for enhancements and new features, so I do need to take into account which ideas are most popular.