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Locus Map - help desk Topic Problem Locus Map (Android)

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Category Locus Map (Android)

Tags elevation, audio coach, elevation gain, altitude gain, elevation filter

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Subscribers 6

Votes 4

Audio coach says wrong elevation gain

jimmyfromthepieshop shared this problem ago

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Good morning fellow locusts,

I like to use the audio coach when running because I'm currently training for a mountain marathon. This means elevation gain is the most important information I want to hear. But it always announces a much higher figure than it should. For example:

On Saturday I ran 1040m vertically up and 1040m down to where I started. Throughout the whole run the audio coach announced a figure around 80% higher than the real figure (which can be seen on the dashboard I use). It can't be up and down added together because then the figure would be too low. Could it be that the figure read out is the unfiltered figure? If so, could this be rectified? I use the "heavy" filter and the barometer and together these are usually spot on with the altitude.

Thanks for the help.

Jimmy

The same problem 0

Replies (2)

Taras D ●

I've reported the same issue here: http://help.locusmap.eu/topic/audio-coach-reports-elevation-does-it-use-settings-in-altitude-manager

Menion explained there is an initial filtering algorithm, while the track is being recorded, followed by a second filtering when the track is saved.

I have the Altitude Manager set to replace all altitude readings with data from SRTM. However, while recording the track, Locus Map uses the 'initial filter' and the Audio Coach reports inflated altitude values. By the end of my walk, on fairly flat ground, the Audio Coach reports I've ascended 50 meters. After saving the track (thereby applying SRTM data), the Statistics page shows the track ascended a more conservative (and realistic) amount of 20 meters.

I've learned to live with it but it does make the Audio Coach's altitude reports much less useful to me.

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jimmyfromthepieshop ●

Thanks for the reply and clearing that up!

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Menion ●

Good day Jimmy, Taras,

sorry for a late answer.

I'm surprised that in hilly areas when using barometer sensor, values are still so different. Relative accuracy of barometer is quite big and computed elevation changes should be quite precise.

Did you tried to use offline elevation files (SRTM) to completely replace measured altitude data? Does it make any difference?

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Taras D ●

I have Altitude Manager configured to use SRTM (Replace GPS values). When walking, Audio Coach reports total altitude and it is always higher than what Statistics reports after I save the track.

For example, after walking a few kilometers, on relatively flat ground, Audio Coach reports 50 meters elevation gain. I save the track, SRTM replaces all altitude values, and Statistics page indicates 20 meters (which is closer to reality).

I would prefer if Audio Coach conformed to Altitude Manager's settings. If Altitude Manager is configured to "Replace GPS values using SRTM" then Audio Coach should do the same.

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Menion ●

Setup of Altitude manager is first in row of all operations that happen with received locations!!

So if Locus Map receive locations from GPS unit, then it firstly replace your elevation with data from SRTM and then!! this modified X,Y,Z coordinates "go" to rest of Locus Map system, so to track recorder, to audio coach etc.

May you please share with me here some "flat" recorded track, at least few km long? I'll gladly test it for a while. Maybe there is some bug I've missed, or I just confirm, that my filtration algorithm needs an improvement. Thanks

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Taras D ●

I have many tracks of my walks but all have been processed using SRTM -> Replace GPS values. Is that OK or do you want tracks that have altitude measurements reported by the GPS (and not replaced by SRTM)?

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Menion ●

Hmm and even for these "replaced" tracks, you expect lower values for total elevation?

If so, then there are two options:

change method how data are extracted from SRTM files. I anyway already use bicubic interpolation, which I believe is best possible option here
filter even more already filtered ( filled by SRTM ) data. Even now it's little weird to filter them in such case

Oki, I'll use some my own tracks, it will be enough. Area around my flat is quite flat :).

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Taras D ●

The tracks with "replaced" values (from SRTM) are fine. I don't expect them to have lower values for total elevation.

While I am walking, I do expect Audio Coach to report altitude based on SRTM values (because that's what I have set in Altitude Manager) and not based on filtered GPS values.

At the end of many of my walks, Audio Coach reports the total elevation gain was 40 or 50 meters. After saving the track (SRTM -> Replace GPS values), the Statistics page shows the total elevation gain was 20 or 25 meters (which is closer to the truth). Audio Coach is clearly not using SRTM data while I am walking.

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Menion ●

This will be hard ... :). In case, you have defined "Replace elevation by SRTM", then values that audio coach speak are! based on these replaced values. They are replaced immediately when Locus receive a new location and old original measured values are immediately lost. Difference you hear during and after recording is based on strength of filtration used during and after recording. Anyway if export track to GPX (or easier CSV) and sum manually differences in elevation, it will be for sure more then what Locus reports, even that these values will be from SRTM files.

Never mind ... there is currently nothing I may simply change. If so, this needs a complete rewrote of filtration system in app on more places.

I'm sorry, for now, I'm closing it. Changes will be done hopefully in the end of the year, when I expect one more guy that will help me directly with Android code and that has a lot higher skills with these algorithms then me ... thanks for understanding.

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jimmyfromthepieshop ●

I don't use SRTM because it isn't accurate enough. Traveling along a road which is flat but follows a cliff, for example, results in wildly inaccurate elevation information. The barometer works really perfectly and I bought the phone partly because of this feature :-)

I have set up a dashboard which reports the correct elevation gain very accurately on the fly (I have thoroughly tested this) so isn't it possible to just have the voice report the same figure???

I'm no programming expert though so maybe it's not as simple as I think, but where I run it's often wrong by hundreds of metres so a fix would be ideal otherwise maybe remove this feature??

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Audio coach says wrong elevation gain

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Elevation gain in audio coach

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