Differences with ascent between Land and Wikiloc using same GPX track.

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  • Hello,

    This isn't the "real" support. It is the Community of Users.

    For the support you must "send a request".

    Before, you can read: https://support.twonav.com/hc/en-us/articles/115003412052-Track-with-conflicting-distances

    An user.

    Best regards

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    Jose Miguel Ordax Cassa

    Ah, I see. Got it.

    Interesting link but it is related to distances, not to altitude/ascent that is my case. Distances are usually almost the same between both tools, the huge difference is around ascent and I would like to understand why. Perhaps it is not a bug or defect in any tool but a different concept in each one and I am misunderstanding it.

    Anybody from the TwoNav community who has seen this behavior and know why it is happening?

    Thanks again!

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    Thierry CHARLÈS

    Hello,

    Yes it is perfectly known and understood,

    The first problem is related to the precision of the altitude delivered by the GNSS which is noisy (it varies around the true value). This is widely documented on serious websites that show how the GPS system works.

    Therefore, the first question is how the altitude of your track was determined?

    Then, given that the altitude obtained from the GPS (and other GNSS) is "unreliable" (noisy), some websites replace the altitude obtained from the tracks by an altitude obtained via a digital terrain model. However, current global models are unreliable.

    Second question: What does Wiki Loc do?

    Then, Land does not replace the altitude of the tracks, we can correct it (tool menu / calculate the altitude ...) but this assumes that the format.cdem map that you have opened is reliable (French users have files reliable). It is possible to give you the user manual to create your reliable card.cdem for your country.

    So if the altitude of the track is reliable, Land's altitude will be reliable.
    Then the calculation of the slope, in versions prior to 8.9.5 is sometimes crazy, I have not yet checked if this bug has been corrected since 8.9.5.

    Open these tutorials (French), with Google and click on the icone to translate those "tutos" to  your langage,  all the aspects related to altitude are documented.

    1. https://blog.utagawavtt.com/fr/blog/altitude-gps-strava-inexacte
    2. https://blog.utagawavtt.com/fr/blog/comment-installer-mnt-gps-twonav
    3. https://www.actuduvttgps.fr/2020/09/17/climbpro-versus-twonav-comment-visualiser-le-des-montees/

    My GPS is configured in altitude mode = baro + GPS, I have a very precise altitude. The slope indication with the GPS is good. The altitude in the correct Land (on the sites it depends on the sites .. they tend to substitute the altitude of the track by their own data).

    How I validated, the calculation of the altitude by my GPS (Or Land when the altitude of file.cdem is reliable) by comparing the vertical profile to that read on a map (Level curves), the difference is less than 5% which is extremely precise.

    Bonsoir,

    Oui c'est parfaitement connu et compris,

    La première problématique est liée à la précision de l'altitude délivrée par les GNSS qui est bruitée (elle varie autour de la valeur vraie). Ceci est largement documenté sur les sites sérieux qui exposent le fonctionnement du système GPS.

    Par conséquent, la première question est de savoir comment l'altitude de ta trace a été élaborée ?

    Ensuite étant donné que l'altitude issue du GPS (et autre GNSS) est "peu" fiable (bruitée) certains site internet remplacent l'altitude issue des traces par une altitude obtenue via un modèle numérique de terrain. Or les modèles mondiaux actuels sont peu fiables.

    Seconde question : Que fait Wiki Loc ?

    Ensuite, Land ne remplace pas l'altitude des traces, on peut la corriger (menu outil / calculer l'altitude...) mais cela suppose que la carte format.cdem que vous avez ouverte est fiable (Les utilisateurs Français ont des fichiers fiables). Il est possible de vous communiquer le mode d'emploi pour créer votre carte.cdem fiable pour votre pays.

    Donc si l'altitude de la trace est fiable, l'altitude de Land sera fiable.
    Ensuite le calcul de la pente, dans les version antérieure a 8.9.5 est parfois farfelu, je n'ai pas encore vérifier si ce bug a été corrige depuis 8.9.5.

    Ouvrez ces tutoriels (Français), avec Google et cliquez sur traduire tous les aspects liés a l'altitude sont documentés.

    Liens vers les Tutos

    Mon GPS est configuré en mode altitude = baro + GPS, j'ai une altitude très précise. L'indication de pente avec le GPS est bonne. L'altitude dans Land correcte (sur les sites ca dépend des sites.. ils ont tendance a substituer l'altitude de la trace par leurs données propres).

    Comment j'ai validé, le calcul de l'altitude par mon GPS (Ou Land lorsque l'altitude de fichier.cdem est fiable) en comparant le profil vertical a celui lu sur une carte (Courbes de niveau), l'écart est inférieur a 5 % ce qui est extrêmement précis.

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  • To compare ascent, you have to start with a clean track. A correct distance.

    Zoom very hard your track, follow your track and you'll see the picture above.

    After you must have the same source of elevation. A file of altitude (CDEM, MNT...), altitude by GPS, barometric altitude....

    The sames steps between points of your GPX. 

    Some sites reduce the number of points.

    Best regards

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    Thierry CHARLÈS

    Comparison of a track recorded this afternoon.

    GPS TRAIL 2 => Altitude = Baro + GPS (values are exact)

    The vertical profile traced by Land and the one Traced by Komoot (which imports the track) are identical (On strava it will be exaggerated by several hundred meters because Strava substitutes its altitude data for that of the track)

    On the slope side, the two tracks have steep slopes around 20% at the same places, which is true and corresponds to the terrain.

    Land shows some excessive portions above 20% which is false. This is version 8.9.6, but in the previous version 8.9.2 it was sometimes 40% worse instead of 10% I have to fine-tune the Land settings to see if this phenomenon subsides or persists.

     

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    Thierry CHARLÈS

    Hello,

    The difference between Land, WiKiLoc and Komoot for my track recorded yersterday by my GPS is less than 6% (MTB). There is no error in Land or WikiLoc or Komoot.

    If you are an Hiker, the very low speed of the Hikers, can add a lot of false points (fix) due to the GPS precision. Between two records the GPS error is greater than your walk move. You must record ypur position with a step of 10 or 15 m or greter than 5 seconds. In the better case the GPS error is lees than 4.5 m for 90 /100 records, in this case your speed must be greater than 5km/h to record true points. But in montains, forest, or many others case the GPS précision is bettween 5 to 10 m, if the moving speed is less than 10 m /s or 5 m / s fos those exemple it is better ton reduce the GPS record cadence to avoid a track with a lot of errors .

    Good Hikes

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    Jose Miguel Ordax Cassa

    Thanks a lot for your explanation Thierry.

    It seems my GPS (GPSMap 62) hasn't barometer for altitude and as you said, I am a hiker and I don't think I walk too fast, so I think the recording I get from the GPS won't be very accurate. I will study how to setup the GPS to record less points and test new recordings.

    Meanwhile, I found very interesting the option "tool menu/calculate the altitude...". I use Spain_Topo_IGN.cwms map from On-line files option within Land. Do you know if it is accurate for altitudes? It could be an option to fix my recordings.

    Finally, for your last post, in my case most of the times the maximum altitude, minimum altitude and distance match between different toolings. The issue only appears with the cumulative ascent. There is where the differences are huge.

    Thanks a lot!

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    Thierry CHARLÈS

    Hello

     

    The GPS does not know the level curves, it is necessary to adjust the accumulation step with a homogeneous value of that used for the level curves of a map (5, 10 or 20 m) according to the relief.

    If you don't have a baro sensor, on your return trip with Land; right click on the track / tool / calculate the altitude.

    But first, watch my tutorials and make your own CDEM from the sony database, this source is not perfect but it is precise.

    It is enough to import the altimetric data of Spain, then with Land to merge them in a CDEM.

    I think our friend Laurent who straddles the Franco-Spanish border has already this map where he will help you build it.

    Best regards

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    Thierry CHARLÈS

    Hello,

    The new GPSMap 62 had a barometric sensor and more!

    Reduce the FIX recording cadence (15 m or interlligent !) and tune the GPS option ..

    Best Hikes

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    Jose Miguel Ordax Cassa

    Yes, I know. New models have better sensors but mine is the old one. I am downloading the GPSMap 62 manual to check if I can setup the recording cadence.

    Thanks again for all the explanation.

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  • Hello,

    I didn't follow your entire conversation and I don't know if you mentioned the "minimum height to accumulate" setting. If Land accumulates every meter of elevation and Wikiloc only accumulates if 10 meters have been climbed .....

    Mr Charlés is a perfectionist and sportsman. I am only a walker who takes advantage of the landscape, stops for the photo. I am not looking for performance analyzes.

    Yes, I often walk on the Franco-Spanish border but I stay close to France and the French digital models overlap enough for me.

    The Spanish IGN has been offering its maps free of charge for a very long time, unlike our IGN which is just beginning to do so and under certain conditions.ISpanish IGN offers a download site in 3 languages!

    https://centrodedescargas.cnig.es/CentroDescargas/index.jsp

    Saludos

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