Optimize altitude during import

Tring shared this idea ago

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Good evening Sir,

I was looking for a new app compatible with IGN as the one I have been using so far is no longer maintained, so I installed Locus Map to give it a try before purchasing the pro version. I find that there are many nice features, but unfortunately, the elevation gain calculation (and also the speed but it is of lesser importance for me) is too far from what other apps or sites (such as VisuGPX) give when using an average filtering method. As it is one of the main expectations from such an app, it is very annoying that settings do not allow the user to choose the strength of the filtering applied for stats when a new track is imported. For example, the above mentionned VisuGPX let you choose the threeshold and number of points, when you upload a track. I think it would be a very appreciated option.

Thanks.

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Replies (2)

Menion ●

Good day Tring,

if I understand correctly, the problem are not altitude values in own recorded tracks directly in Locus Map, but in tracks that you import into Locus Map right? It is correct, that application considers imported tracks as 100% correct and do no modifications with it's data. The only existing option is "Update elevation" (directly during import) or "Fill elevation" (in tools of existing tracks). Both functions overwrite all altitude data with elevation values from offline HGT files. Anyway, both features are available only in Pro version.

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Eldin ●

Hi,

As a regular user of Locus Map, I can confirm that such a feature is lacking, as elevation gain calculation is erroneous for most tracks downloaded from hiking sites, even after normalizing altitudes. The reason is that the GPS coordinates recorded during the walk can be more or less erratic, specially when the log frequency is high. Fixing altitudes, or ensuring that recorded altitudes are precise by using the built-in barometer for smartphones equipped with this component, do not prevent elevation gain calculation from overestimating the value if the track zigzags around the real followed path, typically if you walk along a cliff or mountainside.

As you already implemented an algorithm for filtering altitudes during recording, would it be that complicated to let the user reckon on that same process when importing or analyzing an imported track, as the OP requests (and as the site he quoted does) ?

Thanks.

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Menion ●

Hello Eldin,

in case, you expect that imported track does not have already filtered elevation values, isn't then easier to use "update elevation" during import and let Locus Map fill computed elevation values to whole track from the pre-downloaded offline elevation files? Than statistics should be a lot more precise (compare to jumpy GPS) and mainly united across all imported tracks.

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Eldin ●

Hello, and thank you for your answer.

I am afraid the solution you propose will only work if the GPS track is clean as far longitude and latitude are concerned. Then, the "update elevation" feature will set the right altitude value from the elevation model.

But, if your recording is erratic and you are walking along a cliff, then the process will alternately fill the altitude field with the right value when the GPS position is exact, but a wrong altitude when the GPS position is offset. So, imagine your GPS position oscillate 10 meters between the right coordinates (because of echoe for exemple): the imported altitude will be sometimes exact, sometimes underestimated of about 2-3 meters, and the elevation algorithm, without a filter, will calculate an elevation gain for each variation. At the end of the day, you will overestimate your total elevation gain about several dozens of meters.

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