Gpx track elevation inconsistency after update elevation

[markopolo]

Dear LM users,

I have a question regarding "update elevation" feature and what/how it actually does. I am seeing (too) large increase in elevation after "update elevation" use on imported GPX tracks and on recorded ones.

I downloaded following GPX and followed it on bicycle:
https://drive.google.com/file/d/1DaYc2Gx8Fn1IBsduxEbepS9O_UNh5OXa/view?usp=drive_link

When I import it elevation shows:


After "update elevation" it shows:


According to my Garmin watch, actual measured elevation is very close to 1030m, rather then 1666m...

What could be the issue for this? I also noticed this in cases where I record track with LocusMap and later use "update elevation". The change in elevation is significant.

Thank you

[michaelbechtold]

Interesting case indeed. Root cause of differences are the two fundamentally different data sources
- track recording, regardless if by Locus, any other app or Garmin is they rely on GPS signals from satellites. Reflections, blockages, spoofing and alike impact those, by physical effects. In particular the elevation data is not too reliable. You can see horizontal and vertical fluctuations when you look at the graph.
- update elevation on the other hand gets its data from DEM data files. Typically 3" (90m) resolution, but Sonny's data has 1" (30m) resolution for most of Europe. Typically an "update elevation" will reduce the flucuations, hence reduce the gain/loss totals rather than inflating them.
I'd look at the graphs to see if the updates curve as visual anomalies.
And I'd check if using Sonny's 1" data gives better results.
Cheers
Michael

[lor74cas]

Umm max Speed 1753 km/h you are faster than Flash!
I think there are some points on the track recorded with a bad accuracy, take a close look at the points of the track if you find some bad point delete it, I think they are the cause of the crazy max speed and crazy altitude.

[Menion]

Interesting, agree.

Original track
- https://link.locusmap.app/t/wny1ck

Filled with (app provided 3'' HGT files)
- https://link.locusmap.app/t/wny1ck

Filled with (Sonny's 1'' HGT files)
- https://link.locusmap.app/t/msfw7o

Seems that original track is just well optimized.