Error in elevation calculation in tracks

Thomas Stöckel shared this question 32 days ago
Answered

Hi,

I created a track in the app. Then clicked on the track to select a specific location, basically my first supply station. The small window which appears shows distance from start (3.9 km), D+ (2531m) and D- (-3364m)) to finish (screenshot Screenshot_20240521_213116_Locus Map Classic.jpg).

From the overall statistics of the track you see total D+ (3511) and D- (3509) (screenshot Screenshot_20240521_213124_Locus Map Classic.jpg).

I'm subtracting the value of the small window from the total value to get D+ (3511m - 2531m = 980m) and D- (3511m - 3364m = 145m) for the specific location.

When creating the track, the route to this specific location is showing just 844m D+ and -10m D- (screenshot Screenshot_20240521_213150_Locus Map Classic.jpg).

I've check with another track, same issue. I've tested Graphhopper, BRouter and different hiking profiles. All the same.

My environment: Samsung S23+, Android 14, Locus Map Classic 3.70.9, maps: openandromaps (Alps East).

Can you please check.

Thank you and best, Thomas

Replies (7)

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Hi Thomas,

Locus Map displays positive and negative cumulative elevation gain on the track point detail, not just a difference of elevations. Therefore it is not possible to simply subtract part of the track from the whole track. The cumulative elevation gain of a track part from A to B is not the same as the cumulative elevation gain from B to A. More about elevation gain calculation >>

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Hi Michal,

CEA is clear for me. But I don't get you answer regarding the track point detail. From my expectation, the track point detail should show me the relative data either from the start or to the finish: distance, D+, D-. You are saying it isn't? But then, where else would I get the data from?

Best, Thomas

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The trackpoint label:

d14480684db315a0e6925cc5cefd16c8

1 - distance to the start of the track

2 - distance to the destination

3 - elevation of the trackpoint

4 - negative elevation gain to the destination

5 - positive elevation gain to the destination

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Hi Michal,

thanks, but that's all clear to me.

You might misunderstood my question. Again, back to my example, and that's why I was filing this as a bug.

Let's go back to my screenshots I had attached. The selected track point shows D+ and D- gains to destination. I wanted to know the D+ and D- gains from start. Thus, I did the math and substracted these values from the track's overall D- and D- gains. This should give me the D+ and D- gains from start for that track point. Correct? Now exactly here is the issue, my calculated value is wrong. The last screenshot proofs this: it's another track I created for testing, which just goes to the selected track point and it shows different D+ and D- gains from start (in the footer).

Best, Thomas

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Another hint: the track when imported in outdooractive has far less D+/-. So the root cause could be a bug in your D+/- calculation. That would explain.

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Hi Thomas, first of all, forget about the Outdooractive-values, I think they are mathematically attanued a little bit too much, i.e they are too low.

I'm also using Locus Classic, so loading your gpx-track I should get the same values as you did - but i did not. Are you using Sonny 1" elevation files of Germany? If not - please copy them into Locus.

After importing your track, Locus (without elevation update after import) I get: -3376m / +3377m

After elevation update (with Sonny 1" files): -3304m / +3305m

Locus Web planer after import first writes "3377m" only and after clicking onto the track-icon we see more detailed statistics, with surprisingly changed values: -3509m / +3512m

If you are getting the same values with Locus Classic as I did, we can move on to your actual question regarding elevation gain/drop from start to the current waypoint

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I already can confirm your observation: If I'm clicking onto the start-trackpoint I don't get the elevation sums of the total track listed above, but just: -3187m / +3188m

So maybe both methods are different although they should be the same: how Locus calculates a) the elevation statistics of a whole track and b) how the elevation sums to the the track-finish of a clicked trackpoint

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Hi Sonny,

thanks for checking and confirming and for pointing to the more detailed elevation files.

Best, Thomas

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Hi guys,

I'm worried this is a result of the out-dated algorithm used in the Locus Classic.

I'm testing it in the new Locus Map 4 and value forward and backward visible directly in the trackpoint detail (see screenshot), seems to be correct.

Because it is not a critical problem, it won't be updated in the Locus Classic, thanks for understanding.

e4e740b2dc7ff62a8b9355c8f56f89ea

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Hi guys,

actually, there was a bug associated with elevation data and the altitude threshold. Thanks for reporting it, the bug will be fixed in the next app version which is coming probably the next week.

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Thank you very much.

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