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Difference in elevation uhill/downhill reported

Marius Moldovan shared this problem 6 years ago
Not a Problem

I took the same track with a Garmin Montana 650 and also with locus pro


Locus reported Elevation Uphill 1033 m. The same track from Locus put in Garmin Basecamp,reported Ascent 1234 meters.

The track from Garmin montana reported in Basecamp, Ascent 632 meters.

Which is OK ?

here are the 2 files

Replies (5)

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OK is the one, that gives the about same result as evaluating of the accurate topographic profile. Unfortunately, there is no a priori given correct way to calculate the correct elevation total ascend. Too weak filtering of noisy data leave noise a/o artefacts, giving too high value of the ascend. Too strong filtering reduces the noice and artefacts, but also smoothes the local real terrain features.

There are several ways to get altitude data of various quality ( GPS, barometer, varioius flavours of SRTM or similar ). The most proper available way is using barometric altitudes ( if a device offers that ). If not available, then SRTM ( or more accurate alternatives ) based altitude profile, if local or remote SRTM data are available.

There are multiple ways to process these altitude data, concerning raw data noise ( like GPS ) or artefacts or approximations ( like SRTM ). With properly set processing strength one can get the correct result, but one cannot know in advance what strength should be used for particular case. What makes sense is try to match processing of lower quality source to result of higher quality source processing.

As far as I know, Locus offers the option to replace noisy GPS based altitude profile to less noisy SRTM based profile. What is Garmin device/application way to process data I do not know.

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Thanks for the explanations..


My phone doesn't have barometric sensor, so I had in settings Optimize altitude values with SRTM values(not replace)

I had my filter set to medium..

So maybe it would be better with the heavy filter? I do not have reference values/etalon in order to "calibrate" the amount of filtering..

Or with completely replace gps based values with SRTM?But one can not always trust the quality of the SRTM altitudes for all regions ?!

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I guess Optimize GPS altitudes with SRTM data makes a trade-off for filtering GPS noise and avoiding SRTM artefacts. As you have no physical reference to adjust, you have to know why you do what you do.


A rule of thumb can be :

If elevation ascend is with in Optimize + medium filter *regularly and significantly* higher than SRTM based ( replace mode ), set stronger filtering, as there is too much residual noise. Or, if you cannot, switch to the SRTM replacing.


If elevation ascend is with in Optimize + medium filter *regularly and significantly*

lower than SRTM based ( replace mode ), set weaker filtering, as terrain features are smoothed.


Otherwise let it be.


Note that the flat a/o steady terrain may need stronger filtering to approach real value than steep a/o complex terrain. OTOH, you may want the constant approach.

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Additional information about this topic can be found here:

http://help.locusmap.eu/topic/calculation-of-elevation-data#comment-39771

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Libor, thanks for the scientific approach :) tarasD, you're right, we discussed this topic a week ago.

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